Med. J. Malaysia Vol. 39 No. 1 March 1984

C)

PERSPECTIVES IN MEDICINE: MALARIA

A. A. SANDOSHAM

Colonisation of the Tropics

held then on various aspects of the disease, and totrace through the years of development andacceptance of progressive scientific views, is a subjectof absorbing interest.

The occurrence of malaria is traceable to theremotest antiquity as judged by the references tothe seasonal occurrence of intermittent fevers inancient Egypt, India and China. Hippocrates, theGreek physician in the fifth century before Christstudied the clinical picture of malaria, recognisingthe different types of periodic fever. Little progresswas made concerning the disease until 1640 whencinchona was introduced into Europe from Peru. Itwas specific for malaria and enabled the physiciansto separate it from other fevers with which it hadbeen confused.

A hundred years ago, the Europeans commencedthe colonisation of the tropical region and openedup the countries for agriculture, commerce andindustry. Throughout the history of tropicalenterprises, the opening up of a country by fellingjungle and planting, building roads and railwaysetc., was always followed by violent outbreaks ofmalaria (Fig. 2). This exerted a profound influenceupon the colonialists as well- as the indigenouspeople, affecting their health, vitality and retarding

Fig. 1 Professor A. A. Sandosham MD DSc JSM PJK. their physical development, social, intellectual andProfessor of Parasitology, Singapore 1950 - 1960. political progress.Author of Malariology with special reference toMalaya 1959. Senior Malaria Research Officer1961 - 1%3. Director of Institute for Medical Need to resolve problems locallyResearch 1964 - 1965.

To envisage the malaria situation in the world ingeneral, and in the Malay Peninsula in particular,a hundred years ago with the vague empirical beliefs

INTRODUCTION

Malaria is a disease of man caused by the malariaparasites of man and transmitted from man to manby the bite of infective anopheline mosquitoes. Thedisease manifests itself, among other signs andsymptoms, with- the occurrence of intermittent fever.

Professor A. A. Sandosham

c/o MMA Secretariat

P. O. Box S-20, Sentul, Kuala Lumpur

The problems of malaria vary from place to placeand it is necessary to define and resolve the problemsin each territory. The blind acceptance of conclusionsarrived elsewhere and the adoption of measures

5

_MalarlQ

0 -0 Aubbtr planting"'0

2'

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IS

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1890 '900 1910 1920

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": \I'.IIII..., ,

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120

100

80

60

20

Fig. 2 Rubber planting and malaria(Courtesy: Malariology).

found satisfactory to deal with malaria in othercountries, do not always meet with success locally.Malayan workers investigated their problems locally;these will be dealt with later under appropriatesections.

THE MALARIA PARASITES

The close association between swamps andmarshes with malaria had long been noted. It wasthought to be due to miasma or foul air (hence theItalian term Mal aria) or its close association withswamps (hence the French name paludisme) usedto describe the disease.

Discovery of Malaria parasites

Since the days of Pasteur and other workers,it became evident that microscopic organisms invadedthe human body and caused the illnesses of man.Malaria pigment was recognised in the tissues of thebody in malaria cases. However, it was not till 1880that a French army surgeon in Algeria, Dr AlphonseLaveran (Fig 3), first noted and described malariaparasites in the red blood cells of a patient. Heexamined fresh blood (liquid and unstained) andnoted exflagellating forms from crescents whichhad rounded themselves. His discovery was eitherignored, explained away or rejected as simply beyondbelief for four years. Scientists were on a look-out fora bacterium of some sort.

Subsequently, other workers described in detailand named the malaria parasites of man as:

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Fig. 3 Or Alphonse Laveron MD, the discoverer of themalaria parasite(Courtesy: University of Malaya).

Plasmodium malariae Laveran, 18~n; Plasmodiumtnuax Grassi and Feletti, 1890: Plasmodiumfalciparum Welch, 1897; Plasmodium ovale Stephens,

1922.

To this list must be added the parasites of non­human primates which have been implicated, thoughrarely, as natural infections of man namely:Plasmodium cynomolgi bastianellii Garnham, 1959;Plasmodium knowlesi knowlesi Sin ton and Mulligan,1932;Plasmodium simium Fonseca, 1951.

Of the above three species, Eyles et al, foundhuman infections of Plasmodium cynomolgi froma monkey source (Macaca fascicularis) which hadbeen taken to the United States from the east coastof the Malay peninsula. Chin et al., reported a caseof an American surveyor who had acquiredPlasmodium knowlesi knowlesi infection whileworking at night in the jungles of Pahang, a state inthe Malay Peninsula. Yap et al., reported anothercase of a Malaysian with naturally acquired P.k.knowlesi infection.

Improvements in staining

In 1891 Romanowsky introduced oxidationproducts of methylene-blue (such as methylene­azure) to eosin (an acid stain) and methylene blue(basic stain), in stains which resulted in differentialstaining of the varying cellular elements, for examplethe chromatin of the malaria parasite staining a deepred (Romanowsky effect). Modified Romanowskystains like Leishmans and Giemsa work best whenthere is no acid or alkaline bias thrown againsttheir action by changes in the reaction of the diluent.Within recent years, there has been a tendency touse buffer solutions as diluents. The reaction ofbuffer solutions remains stable even when exposedto the action of small amounts of acid or alkali; inother words they act as a buffer against abruptchanges in pH. Field and Sandosham (1964) havepointed out that the aqueous stains show a definitesuperiority over methanolic stains. The introductionof the Romanowsky stains has enabled workers torecognise malaria parasites easily and describe themmore accurately.

Electron-microscopic studies

The electron microscopic study of malariaparasites has revealed that the ultra-structure of thedifferent species is generally similar except in theerythrocytic stages which is related to the intake anddigestion of food by the parasite from the host cell.

The recently developed techniques for thecontinuous cultivation in the laboratory of theasexual erythrocytic satges of P. falciparum bringsthe day for vaccine production against this species

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Fig.4 Dr Hamilton Wright MD, Organiser and first Directorof IMR, Kuala Lumpur 1900 - 1903. Author ofThe Malaria Fevers ofBritish Malaya 1901(Courtesy:IMR).

nearer. In vitro cultivation has opened up theopportunity for carrying out experimentalchemotherapy to assess the sensitivity of parasites todrugs. The ability to produce large quantities oferythrocytic-stage parasites will enable them tobe used as antigens in immunological investigationsand serodiagnosis.

The strains of malaria parasites

Within each species of malaria parasites, theremay be different strains, antigenetically different.The strains may exhibit varying degrees ofsusceptibility to drugs and in,fectivity to vectors.There may also be differences in the incubationperiod, perpatent period, latency period, frequencyof relapses, numbers of merozoites in matureschizonts, etc. Three strains of P.vivax were recentlyisolated in Malaya (Field et al., 1965)

Work in Malaya

In Malaya, the work of Wright (1901) (Fig. 4)

had established the presence in the country of P.vivax, P. falciparum and P. malariae. It is doubtful ifP. ovale is endemic in this country although ovale-

like parasites have occasionally been seen, whichcould have been variants of P. vivax. The' spotty'distributions of P. malariae all over the world and itsspecial association with the aboriginal inhabitantsof a country rather than with its immigrantpopulation has been noted in the Malay Peninsula.It was probably more prevalent in the early days ofMalayan history than at the present time. Figuresquoted by Wright (1901), Darling and others(1915-1917) give a percentage incidence ofabout 20 whereas the present-day percentageincidence is between zero and seven. It may howeverbe the dominant species in isolated places. In a recentsurvey of some rural valleys in Negeri Sembilan,it was found that out of 1000 people examined, 181were infected and 115 of these people were infectedwith quartan parasites. Without any controlthe quartan infection dropped in a few years to9 out of 69 per 1000 examined. Green (1931)examined 165 Sakais (an aboriginal tribe) and foundP. falciparum, P. vivax, and P. malariae and mixedinfections, distributed in the proportion of 3: 1: 3: 1.Thomas and Dissenaike (1977) detected fluorescentantibodies in 89% of the Malayan aborigines withP. falciparum antigen and 62% with P. brasilianum(for P. malariae) antigens.

Malaria parasites of non-human primatesThe importance of the study of parasites of

non-human primates was evident from the discoveryof pre-erythrocytic stages in the liver of monkeysinfected with Plasmodium cynomolgi bastianellii byShortt and Garnham in 1948.

Eyles et al., (1960) showed that Plasmodiumcynomolgi bastianellii of a macaque could betransmitted to man by mosquito bites. Rodhain hadshown that Plasmodium malariae occurs in Africanchimpanzees and that man is readily susceptible tothis strain and vice versa. However, the likelihood ofman becoming infected in nature with Plasmodiummalariae from the ape source is small- but thereare places where monkeys live in close associationwith man, both infected with closely related malariaparasites, hence the greater chances of being bittenby the same anophelines. In such placesmalaria may prove to be a zoonosis and monkeyscould be a reservoir of infection as in yellow fever.The study of this problem was considered important

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and a team from USA composed of Eyles, Warren,Bennett, Dunn and Quinn worked in collaborationwith the staff of the Institute for Medical Researchin Kuala Lumpur comprising of Sandosham, Yap,Wharton and Cheong over a three-year period. Theydescribed several new species of malaria parasites,the various hosts they were found in and theirdistribution in Malaya. In addition to the findingsof Eyles et al., (1960) of the transference ofPlasmodium cynomolgi bastianellii from a monkey

to a man by a mosquito bite, there are two recordsin Malaya of the natural infection of Plasmodiumknowlesi knowlesi in man by Chin et al., (1965)and Yap et al.,(1971).

The experimental infection of the rhesus monkeyby Plasmodium cynomolgi has occupied an importantplace in the testing of new antimalarial drugs.Young's finding that human malaria parasites canbe transmitted to Aotus trivirgatus, a Columbiannocturnal monkey is a new area for chemotherapytests. The animal hosts of human malaria constitutea ready source of obtaining large numbers of thedifferent stages in the life history of malaria parasitesas antigens for immunological studies and thepossible preparation of vaccines.

The malaria parasites of non-human primateshave been summarised in Malariology with specialreference to Malaya by Sandosham and Thomas(1983) and Sandosham (1967) lists records of malariaparasites which have been identified in non-humanhosts in Malaya.

Life history of Malaria

The transmission of malaria from man to manremained a mystery for a long time. There had beenvarious speculations, however they lacked proof.References to the probability of mosquitoes playinga role had been made from time to time. Howeverin 1883, King in an article entitled Insects anddisease mosquitoes and Malaria advanced nineteenarguments in support of the thesis that mosquitoesconveyed the disease. Manson's (Fig. 5) Goulstonianlectures of 1894, based on his previous discovery ofthe mosquito-transmission of the human filarialinfection, were the starting point of the scientificinvestigations of this problem.

It was long assumed on Schaudin' s authoritythat the sporozoites injected into the blood streamof man entered the red blood cells directly. Raffaelein 1934 discovered that avian parasites developedin internal organs of infected canaries. Fairleyworking with human volunteers showed that themalaria parasites disappeared from the peripheralcirculatio-n within about half an hour of injecting

Ross (Fig. 6), at the suggestion of Manson andafter many months of patient research, made animportant discovery in 1"897. He noted early stagesof the development of the malaria parasites of manin the wall of the midgut of the dapple-wingedmosquito. Sadly, he was transferred to a place wherehe could not continue with his life-history studiesof human malaria. He worked on bird malaria andin 1898 worked out the complete life-history insparrows. In the same year, Italian workersdescribed the cycle in human malaria which theyfound to be identical with Ross' s work with birdmalaria and of which work they were conversantwith. In 1900, Manson and his colleagues confirmedthat malaria was transmitted by Anophelesmosquitoes. By protecting volunteers from beingbitten by anopheline mosquitoes in a rnalariousarea in Italy, they showed that infection could beprevented. At the same time infected mosquitoescould be brought from Italy to a non-malariousplace in England and infect volunteers who werebitten by them.

Fig. 5 Sir Patrick Manson FRS. He showed that mosquitoestransmitted filariases to m an and encouraged SirRonald Ross to work on transmission of malariaby mosquitoes(Courtesy: J.D.Gillet).

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sporozoites , malaria parasites reappeared only afterfive to eight days, depending on the species ofPlasmodium, Garnham (1974) in Kenya showedP, kochi of monkeys developing in the liver. Hejoined Shortt in London and in 1948 they discoveredin the liver of a rhesus monkey the pre-erythrocyticforms of P, cynomolgi (closely allied to P. vivax ofman) of a macaque. In the following year Shorttet al., described pre-erythrocytic stages in theparenchyma cells of the liver of P. falciparum inman.

Subsequently, these liver forms were shown to

be present in all human malaria parasites, Thesetissue-forms developed into mature schizonts whichliberated merozoites that entered the red bloodcells and multiplied (schizogony). The completionof the primary exo-erythrocytic schizogony maybe followed by the secondary forms as the resultof re-entry of merozoites in the liver cells. Thesewere regarded as being responsible for late relapsesin malaria, although the latest theory is that certainsporozites remain in a dormant state (hypnozoites)for varying periods and cause relapses.

The distribution of Malaria

The geographic distribution of malaria isdependent on a wide range of climatic factors whichaffect the occurrence and density of vector speciesof anophelines and the development of the variousspecies of malaria parasites on the insect host. Ofthe various factors involved, temperature seems tobe the most important since the boundaries ofmalaria distribution, corresponding roughly tothose of the mean summer isotherms of 60°F(15.5°C) which at their greatest divergenceapproximate to 60 0N and 400S latitude. Withinthis limit malaria occurs at altitudes ranging up to(1524 m) (5,000 ft) to (2,745 .m) (9000 ft) abovesea level; as latitude increases, the maximum altitudeat which malaria is indigenous decreases.

Wilson points out that there is a close relationbetween the mean wet bulb temperature and theincidence of malaria in Malaya. It probably affectsmalaria by its influence on the mosquito since ithas been found that insects have a body temperature

Fig.6 Sir Ronald Ross FRS. He discovered that mosquitoestransmit malaria(Courtesy: J.D.Gillet).

corresponding to that registered by the wet bulbthermometer.

Broadly speaking, the highest incidence of malariawould have been the equatorial regions, decliningas we proceed away from the Equator to the tropical,sub-tropical and temperate zones.

The prevalence of MalariaThe annual incidence of malaria in the world

was estimated in the 1950s 'to be about 250 millioncases with 2.5 million people dying of the diseaseeach year. In 1980, twenty-five years after theinitiation of the World Health Organisation (WHO)programme for the global eradication of malaria, itwas estimated that 848 million people were livingin areas where eradication or control programmeswere in progress and that 343 million (the majorityin Africa) were in endemic areas which were notprotected by any specific anti-malaria measures. It

was also estimated that every year, the disease causesthe death of one million children under the age of12 years.

Conditions in the Malay Peninsula during theclosing years of the nineteenth century can bepictured from Carey' s observations quoted by

Watson (1921) (Fig. 7) on New Amherst Estatein the Federated Malay States, where malaria brokeout in epidemic proportions among a non-immune

community reported to work in a potentiallymalarious area. "Between the years 1892 and 1898there were an average of fifty Tamil women oncheck-roll each year. Yet in the whole period noliving child was born. Several women becausepregnant, but only in one case did the child becomequick, and even in this case the woman eventuallyhad a miscarriage. The estate was so riddled withmalaria that the coolies were all miserably anaemicand lacking in strength and the estate had eventuallyto be abandoned. "The town of Jugra was abandonedat one time while orders were actually sent by telegraphby the High Commissioner to close down Port Klangwithin two months of its being opened, because ofmalaria.

Fig. 7 Sir Malcolm Watson MD. A pioneer malariologist ofMalaya (1901 - 1927) who successfully introducedanti-larval control measures directed specificallyagainst the vectors (species sanitation) (Courtesy:Journal of Tropical Medicine and Hygiene).

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THE TRANSMISSION OF MALARIA

Distribution of Anopheles

There are about 400 species of anophelinemosquitoes in the world and of these, only about60 are important vectors of malaria under naturalconditions. Owing to the limitation of zoo-geographicdistribution, only a small number of these areencountered in any particular region. Malaysia isone of the sub-regions of the Oriental Region butthe border line separating it from its neighboursis not sharply defined and species characteristicof the adjoining sub-regions tend to extend intoits zone.

Even within the confines of the Malay Peninsula,a number of species exhibit a discontinuousdistribution, which may be due in some cases toclimatic differences and in others to the developmentof new species or sub-species by geographic isolation,resulting from land changes in recent geologic times.Another feature of geographic distribution ofAnophelines worthy of note and which is probablyrelated to climate, is that members of the sub-genusA nopbeles are distinctly more numerous in theMalaysian part of the Oriental Region, with itsuniform climate supporting evergreen tropical rainforests. About 60 species and sub-species ofAnopheles are currently recognised as being presentin the Malay Peninsula.

Vectors of malaria vary from place to place;a vector in one area need not necessarily act as avector in another area. The inherent susceptibilityof an Anopheline mosquito for the full developmentof a malaria parasite varies according to the speciesof Plasmodium and its strain, whether or not itbites man repeatedly in sufficient numbers, whetherit lives long enough to permit the development ofthe malaria parasite to form sporozoites whichfind their way to the salivary glands.

Experimental infections

Much work has been carried out in the MalayPeninsula since the turn of the century to elucidatethese points. Attempts were made to establish therelative susceptibility of different anophelines under

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experimental conditions. The introduction of theartificial mating of anophelines has enabled themaintenance of colonies of these insects in the

insectariums.

Eighteen species of five-day-old anophelines werebred in the laboratory, starved and given the sameopportunity of taking blood from gametocyte

carriers. Sixteen days after the blood meal those thattook blood were dissected for evidence of oocystsor sporozoites or both. About 4000 dissectionswere made. The results showed that few, if any,Malayan species of Anopheles are incapable ofbecoming infected under suitable conditions bylocal strains of Plasmodium falciparum andPlasmodium vivax. There are limitations to laboratoryinfectivity experiments in determining the relativeimportance of anophelines under natural conditionsbecause it was found that two inocuous speciesas determined by epidemiologic evidence like A.vagus and A. kochi were found to be readily infected.Other factors have to be taken into account.

Feeding preferences

An anopheline mosquito that showed a markedpreference for human blood (anthropophilic) ascompared with animal blood (zoophilic) mightwell prove to be an important vector of malaria.When attempts were made to test this by givingvarious Malayan anophelines opportunity to consumehuman blood, it was found that A. maculatus, themost important vector, showed the greatest avidity(more than 70% engorging themselves). A. maculatusis a non-vector in Kalimantan (Borneo) and indicatesthere is a geographic difference in the innate degreeof attraction to man in this species.

A comparison of the relative abundance ofdifferent species of anophelines caught in human-baittraps placed near human habitations and at nearbycattle sheds may give some indication of their basicfeeding preferences. When catches were made in thisway on three estates it was found that A. maculatusheaded the list for human-bait trap.

The source of a recent blood meal of ananopheline mosquito can be determined by carryingout precipitin tests. A large number of such tests has

been carried out in the Malay Peninsula and A.maculatus and A. umbrosus head the list.

Epidemiologic findings

The ralative importance of the species ofAnopheles may be obtained by the combination ofsporozoite rates and the numbers biting a personfrom which it is possible to estimate the numberof infective bites. The incrimination of a specieshas often been the result of epidemiologicinvestigations; the occurrence of malaria only wherea particular species was present or where it was thedominant species. With added information regardingfeeding preferences, prevalence and the extent towhich they are found infected in nature, thefollowing list of Malayan vectors can be presented as:

Anopheles (Cellia) maculatus Theobald, 1902;

Length of life

The natural length of life of an anophelinemosquito is of importance as a transmitting agentof malaria because prior to the infective bite, theinfecting blood meal must have been digested, theoocyte matured and ruptured, and the sporozoitesready in the salivary glands for injection. Informationregarding longevity of each species under naturalconditions is, however, difficult to obtain. Parasitesand predators probably take a heavy toll ofanopheline life. Some indication of the natural spancan be obtained by observing the number of daysthat members of each species survive underlaboratory conditions. The maximum age (in days)observed when one blood meal had been takenwas 66 for A. maculatus, 63 for A. barbirostrisand 59 for A. umbrosus, while those of the knownnon vectors were much lower.

AnophelesAnophelesAnophelesAnophelesAnophelesAnopheles

(Anopheles) letifer Sandosham,(Cellia) sundaicus Rodenwaldt,(Anopheles) campestris Reid,

(Anopheles) umbrosus Theobald,(Anopheles) nigerrimus Giles,

(Cellia) dirus Peyton and Harrison,

1944;1925;1962;1903;1900;1979.

Some indication may be obtained of the age ofan anopheline mosquito by noting the degree ofdamage to the wing fringe and the extent to whichthe scales of the abdomen are denuded. The presenceof attached water mites to the body and meconium(larval food) in the stomach are evidence ofimmaturity in mosquitoes. Dissection may show thepresence of retained eggs in ovaries. The sporozoiterate, the proportion that have laid eggs and theappearance of tracheoles in ovaries may give someinformation on the longevity of anophelines.

Natural infections

An opinion as to the danger of an anophelinespecies may be formed by observing the degree ofnatural infection encountered in mosquitoes trappedin the wild. More than a hundred thousanddissections have been made in the Malay Peninsula;in attempting to interpret the findings, it mustbe remembered that often the human-bait wasused and collections were made near labourers'settlements. In some cases, infections could havebeen of malaria parasites of monkeys and othermammals.

To the above list may be added the followingas potential vectors; Anopheles (Cellia) minimusTheobald, 1901; Anopheles (A nopbeles) whartoniReid, 1963; Anopheles (Anopheles) donaldi Reid,1962.

A. aconitus, A. barbirostris, A. sinensis, andA. pbilippinensis; known vectors elsewhere, donot transmit malaria in the Malay Peninsula.

The distribution of vectors

The vectors differ in different ecological zonesaccording to the nature of the terrain and vegetation.Thus, the country may be broadly divided into threemain zones namely, the brackish water zone, thecoastal plain, and the hills and mountains (Fig. 8).Within these categories may be found dichotomiesbased on whether or not the land has been clearedof jungle and cultivated: further subdivisions arealso possible. However, there are no hard and fastlines between these zones. Even if the zones canbe rigidly demarcated and the breeding of thevectors confined to a particular zone, theseanophelines may extend their influence for a distanceof a half a mile or more into neighbouring areas.

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The Brackish Water Zone is a narrow strip alongthe coast extending for varying distances up thebig rivers. In the untouched mangrove swamps, novector species of anophelines breed and the areais free from malaria transmitted by brackish waterbreeders. When the mangrove is cleared and thetidal waters come in contact with the exposedcollections of fresh water, A. sundacus breedsprolifically and becomes responsible for malariatransmission there.

The Coastal Plains, which extend from the tidalzone to the foothills vary considerably in extent indifferent parts of the Peninsula. The vector speciesof the untouched jungle swamps is A. umbrosus.When such a jungle swamp adjoins cleared areasunder cultivation, A. umbrosus emerges from thejungle to bite man living within half a mile andtransmits malaria. When the jungle is cleared forcultivation, A. umbrosus is replaced by A. campestrisand A. letifer.

The hills and mountains intersected by numerousvalleys form the backbone of the Peninsula. Thevirgin hill jungle is sparsely populated but thenomadic aboriginal tribes are infected, transmissionbeing effected by members of the A. leucosphyrusspecies group and A. umbrosus species group.

A.camputri:s

~~A.:svndaicv:s "

~> A.nigllrrimv:s-.G"Z:2/u

Whenever the cover of the jungle is removed fromhilly areas, A. maculatus breeds readily and transmitsmalaria.

CLINICAL ASPECTS OF MALARIA

Malaria is a chronic disease in which a series ofclassical febrile paroxysms occur, separated byapyrexial periods of varying lengths. In its classicalform the febrile attack, which is related to therupture of a sufficient number of mature schizonts,starts after an incubation period of varying lengths(usually eight to fourteen days in Malaysia) afterthe infective bite preceded by prodromal symptomsand a stage of shivering (rigor). The hot stage,accompanied by headache and nausea, is followed byprofuse perspiration and fall of body temperature.The apyrexial interval varies accordingto the speciesof parasite being of 48 hours in tertian infections and72 hours in quartan species.

In areas where the population is exposed to heavyrepeated infections, the people develop tolerence tomalaria in ten to fifteen years at the cost of a highdeath rate among the children. The adults mayhave afebrile parasitaemia or at most develop mildclinical symptoms. This form of immunity is alsostrain-specific, but owing to repeated infections

A. mocutato»

Fig. 8 Distribution and abundance of vectors(Courtesy: Malariology).

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by all strains of malaria parasites prevalent locally,the immunity will be polyvalent.

Diagnosis of Malaria

This is dependent on the finding of the malariaparasites in the blood. The preparation andexamination of thin blood films takes time and oftenclinicians want quick results in order to starttreatment. The thick blood films are an advantagebecause of the concentration of parasites in a smallfield.

Unfortunately, the drying of the thick films andthe staining take time and while satisfactory forsurvey work it is too time-consuming for clinicalneeds. Field (1941) (Fig 9) introduced a rapidmethod of staining thick blood films whichrevolutionised the diagnosis of malaria. Stainingis possible as soon as the thick blood films ceaseto be obviously moist, i.e. usually within a fewminutes of preparation and the films are ready forexamination under the microscope in a matter ofminutes instead of hours.

Splenic enlargement

The spleen plays a large part in the defence of thehost against malaria and increases in size owing tothe circulatory and congestive changes initially.Later the immunologically important lymphoidand reticuloendothelial cells undergo hyperplasia.The spleen enlarges with the febrile paroxysmbecoming large enough to be palpable below thecostal margin in a few days, particularly in children.Occasionally, the spleen becomes abnormallyenlarged, extending well beyond the umbilicus toconstitute the immunopathological entity knownas tropical splenomegaly syndrome or big spleendisease. This condition has not been noticed in thiscountry.

Malarial Cachexia

Persons repeatedly infected by malaria andneglected or imperfectly treated, tend to pass intoa chronic condition known as Malarial Cachexia.The individual is extremely anaemic with earthycomplexion and puffy face. Development is retarded,

Fig. 9 John W. Field CMG MD DSc (Courtesy: Yap Loy Fong),

and children are stunted, while adolescents frequentlyhave undeveloped genitals and child-like appearance.Mental disturbances, fatigue and dislike of mentalwork are noticeable. Impotence and lack of sexualdesire are common. This condition was notuncommon in pre-war years on very malariousestates but is relatively rare today.

Blackwater Fever

This occurs typically in people who have repeatedand severe attacks of falciparum malaria imperfectlytreated. The disease results from an acute haemolysisof the red blood cells, liberating the haemoglobininto the blood stream, in turn producinghaemoglobinuria. This condition is relatively rarein this country but during the War, there was aconsiderable outbreak among non-immunes fromSingapore sent to cultivate a very malarious placein Negeri Sembilan.

EPIDEMIOLOGY OF MALARIA

Even in a small place like the Malay Peninsula,the incidence of malaria, the anopheline vectorsand other factors responsible for malaria varyconsiderably from place to place. A malariologistshould therefore undertake to define the problemin a particular locality before a control programmecould be formulated.

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The epidemiologist is a medical detective whogathers information, analyses it and provides theexplanation and guidance leading to the control,prevention and ultimately the eradication of thedisease from the community.

The epidemiologists have carried out spleenand parasite rates from time to time and determinedthe endemicity of malaria in the different parts ofthe country at the time of enquiry. At the sametime, anopheline surveys have been carried outto determine the local vectors, their prevalence andbionomics. The staff at the Institute for MedicalResearch, Kuala Lumpur have done much toelucidate the malaria problems in the country. Theseinclude Wright, Daniels, Stanton, Leicester,Strickland, Hacker, Pratt, Gater, Wharton,MacDonald, Cheong, Green, Field, Wilson, Edeson,Laing, Sandosham and Yap.

Of the Government and Estate Health officers,special mention must be made of Sir MalcolmWatson, a pioneer antimalaria worker in the country.By careful observations and experimentation, hewas able to recognise the vectors of the tidal zone,the coastal plains, the inland plains, and the hillsand apply specific control measures adapted totheir habits. Other workers in this group includeTravers, Wellington, Howard, Crawford, Barrowman,Wallace, and Waugh Scott.

As a preliminary to carrying out parasite andanopheline surveys, the investigators should acquaintthemselves with the geography and the topographyof the area, provide themselves with an adequatesupply of up-to-date maps and carry out a geographicreconnaisance to determine the number of houses,their location, accessibility, type and the numberof inhabitants. A knowledge of the customs andliving conditions of the people is helpful. Informationshould be obtained of the metereologic conditionsof the place.

Measurement of Malaria

The vital statistics of the place should be obtainedas also the records of hospital admissions andattendances at out-door clinics and travellingdispensaries. Weekly returns of absentees fromschools may also provide a clue to malaria incidence.

Personal interviews of a number of individualsregarding their feverhistories may be helpful.

The determination of the spleen rate is probablythe most important single item which will help oneto arrive at the intensity of malaria transmissionin the district. The determination of the size ofthe enlarged spleen is useful. A parasite survey shouldaim at obtaining not only the parasite rate (thepercentage of people with parasites in any age group)but also the parasite density (the average parasitecount of the group).

Serodiagnostic techniques may prove useful inthe epidemiologic assessment of malaria. It mayhelp to supplement and complement the informationobtained by determining the spleen and parasiterates. Having assembled all the relevant data, theepidemiologist should use his mature judgementto determine the amount and intensity of malaria.

Anopheline survey

This should be undertaken to determine theanopheline vectors in a particular locality and tostudy their prevalence and bionomics with a viewto the application of this knowledge to their control.

The larval survey should be conductedsystematically. The team should be adequatelyequipped with notebooks, pencils, map-tracings,dippers, spoons, pipettes, bottles with blank labelsand some device for carrying them. The larvae shouldbe transported in collecting bottles to the laboratoryfor identification and rearing as necessary. Thelarval and pupal pelts may be preserved and thehatched out adults identified.

The adult survey should reveal information onthe occurrence, density, seasonal prevalence,longevity, feeding habits, susceptibility to infectionand other aspects of the bionomics of themosquitoes. Adult anophelines may be caught inhouses, especially in the early mornings, on mosquitonets, or biting man (bare-leg catch). They may becaught in cattle sheds by automatic trappingmethods', human-bait traps or window-trap huts.The mosquito is best caught by slowly placing overit with the mouth of a test tube. When the mosquitohas flown into the tube, it is plugged with a piece of

15

absorbent cotton wool dampened slightly to preventthe mosquito from dying. It is taken to a laboratoryand identified. It may then be dissected or mountedas necessary. If engorged females are caught, thesource of the blood meal may be identified bymeans of precipitin test. If an anopheline is dissectedthe midgut and salivary glands are examined foroocysts and sporozoites respectively.

Survey report

Having collected the data necessary for makingan epidemiologic diagnosis of the malaria problemof a locality, a survey report should be preparedembodying in a summarised form all the availabledata together with tables, charts, sketches, mapsand photographs.

The report should also give an analysis of the dataassembled, emphasising the relevant facts and theinvestigator's conclusion on the malariaof the locality.

Finally, the report should include an opmlOn onthe practicability of control and antimalaria measuresor combination of measures best calculated to solvethe local problem. If possible, it would be preferableto submit a detailed outline of the project by whichthese measures can be put into operation.

CONTROL OF MALARIA

General principles

According to Watson (1921), when Ross 'discovery that mosquitoes transmitted malariafrom man to man was first announced in 1898,it was treated with undisguised incredulity; whenconfirmed it was said to be intresting but valueless.

Malaya can claim to the honour of being one ofthe earliest countries in the world to have successfullyapplied the knowledge of the mode of transmissionof malaria to its control. Attempting to controlmalaria by getting rid of mosquitoes seemed animpossible task as there are hundreds of these insects.Even when it was established that only anophelinemosquitoes carried malaria, the problem appearedcollosal. No less that 400 species are recognised in

the world today. Luckily, in anyone locality onlyfew of these are present owing to the limitationimposed by zoo-geographic distribution ofanophelines. Even so, in a relatively small place likethe Malay Peninsula, there are no less than 60 speciesof mosquitoes belonging to the genus Anopheles.

Luckily again, it was found that of the anophelinemosquitoes in anyone country, only half a dozenor so were vectors of malaria and that not all of themwere encountered in anyone ecological zone. Therecognition of these facts was due to the genius ofanti-malaria workers like Sir Malcolm Watson and thepainstaking researches of malariologists andentomologists. This knowledge led to much savingof energy, time and money by concentrating one'sefforts against the vector species only (species­sanitation). The raising of the living standards ofthe people is in itself a valuable adjunct to antimalariaendeavours. Several countries of Europe and NorthAmerica found that malaria receded with improvedsocio-economic conditions and without theapplication of any specific control measures againstmalaria, a situation referred to as 'Anophelismwithout malaria'.

Measures directed against aquatic stages

At the turn of the century, it was realised thatit would be easier to attack the aquatic stages of thevectors than the adults on the wing. Even so, thecontrol of malaria by antilarval measures was nosimple matter. Watson (1921) says, " so far fromthe map of Malaya being evenly washed with themalaria taint, violent contrasts have been found indifferent parts and widely different, oftendiametrically opposed methods have been foundnecessary for its control. Some land, when coveredwith jungle, had been found to be malarial andsome non-malarial; some land has become healthywhen cleared of jungle, and some has becomeintensely malarial when so treated; drainage freessome land from malaria, but some remains malarial;some land is malarial whether drained or undrained,whether under jungle or cleared of jungle, somerice fields are malarial and some non-malarial; whilein a single ravine, the various insect inhabitantsmay come and go in the wondrous fashion of afairy tale".

16

A. Contr.t. Invert

B. Conc.r.t. Ilob

C. Contour subsoil drain

O. lrnpt:rvlouli loyer

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H. Sullage drain

I- Turt

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like Paris Green, and by upsetting the ecologicbalance of the breeding places through the

introduction of natural enemies like fish, eliminatingsources of food supply, etc.

Measures directed against the adult stage

Adult vectors may be killed by the use ofinsecticides and other toxic substances distributedin the air in the form of sprays, fumigants, smokes,fogs, etc. The residual insecticides may be sprayedon the walls of houses and other resting placesperiodically. The use of baited or light traps andthe introduction of the natural enemies ofmosquitoes may destroy a number of vectors. Adultmosquitoes may be prevented access to humanbeings by animal deviation, the destruction ofdaytime resting places of vectors near humanhabitations, rendering houses unattractive by creatingrepellant barriers of odoriferous plants and chemicals.

Measures dealing with humans

People may be protected from the bites of vectorsby siting homes half a mile or more from theirbreeding places or screening the houses. The useof protective clothing, mosquito nets, repellantsand insecticides like pyrethrum in atomised spraysare helpful.

Fig. 10 Sub-soil drainage of ravine (Courtesy: Malariology).

It was realised that the multiplication of vectors

may be prevented by removing all potential breedingplaces by filling or drainage (Fig. 10). Localresearches had shown that collections of water maybe rendered unattractive to vectors whose bionomicsis known, by altering conditions of shade, movementof water, the degree of pollution or salinity, theamount and type of vegetation present, etc,. Theaquatic stages can be destroyed by the use of thetoxic substance such as petroleum-derivative oils,contact poisons like DDT and alimentary poisons

17

The prompt and complete treatment with drugsof all infected persons will reduce the number ofgametocyte carriers in a community or reduce thenumber of gametocytes undergoing development inthe body of the vectors. It has been shown that theadministration of suppressive doses of drugs willkeep malaria parasites (including gametocytes) lowin the peripheral circulation during that periodthus preventing vectors from becoming infective.

A hundred years ago, we were aware of the valueof the quinine in the treatment of malaria althoughthere were instances of doctors resorting to blood­letting. The bark of the cinchona tree was broughtto Europe from South America by the Spaniardsabout the year 1640 for the treatment of intermittentfever. Subsequently, one of the alkaloids with thetherapeutic effect against malaria which was first

isolated, namely qumme, held a dominant positionuntil World War 1.

When the Germans found themselves cut offfrom their regular source of quinine which mainlycame from Java, India and Sri Lanka, theysynthesized pamoquin and mepacrine. Because ofits toxicity, the former did not come into generaluse and the Germans synthesised chloroquine. DuringWorld War H, the British produced proguanil, and theUSA and UK subsequently introduced

pyrimethamine. Since then sulphones andsulphonamides have been added. Fansidar (acombination of sulphadoxine and pyrimethamine)and mephloquine are found effective againstchloroquine-resistant falciparum malaria. Repositorydrugs with long-acting injectable prophylactic actionare under field trial.

Had this information been used by our troopsfrom the early days of World War H, thousands oflives would have been saved. Since the last war,chemotherapeutic research with the newer drugs hasbeen continued by Field, Wilson, Edeson, Laing,Ponnampalam, Andre, Lewis and Dondero in this

country.

The main purpose of collective drug prophylaxisis to protect the population undergoing prophylactictreatment from the direct clinical manifestationsof endemic malaria in order that its working capacitymay be safeguarded. The plantation population,labour forces on temporary construction workand military forces have been successfully dealt withby this method. School children have been dealt withby teachers with little additional trouble.

In 1921, Fletcher began inquiries in Malaya onthe possibility of devising improved methods oftreatment of malaria by quinine or other alkaloidsof Cinchona. Green, Wallace, Field, and Niven madevaluable contributions to chemotherapy and theprophylaxis of malaria in this country. Field andcolleagues established the high suppressive value ofatebrin in those living in areas of heavy transmissionof malaria (Fig. 11).

Field and Edeson (1949) first established thedevelopment of resistance to proguanil of P.

[alciparum and later by Wilson et al., (1953) ofPlasmodium vivax m Malaya. Cross resistanceappeared and it was established that Plasmodiumfalciparum resistant to proguanil became resistant topyrimethamine also. Chloroquine had held adominant place in malaria therapy for nearly twodecades but Sandosham (1963) showed the existenceof chloroquine resistance among the indigenous

JAN1938

NOV

o...3:o...'"><..-'>­:tQ,

o0:Q,

SEPMAY JULI 9 3 7

--- STABLE POPULATION

------- NEWCOMERS

MAilJAN

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••,,•I

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20

50

... 302...UIX...Q,

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Fig. 11 Malaria in estate with atebrin prophylaxis (Courtesy: Malariology).

18

population in North Malaya. In some cases, theyshowed cross-resistance to amodiaquine andmepacrine. The presence of chloroquine-resistantfalciparum malaria has also been noted in otherparts of Malaya mostly consistent with laterecrudescence RI type.

ERADICATION OF MALARIA

Although the concept of the complete eradicationof malaria from the world had been accepted asfeasible by the World Health Organisation as early as1955, Malaya, unlike some of its neighbours, hadnot initiated a nationwide campaign until 1967.This delay may at first appear strange, consideringthat Malaya has been a pioneering country in malariacontrol. But for one thing, Malaya has beenpreoccupied with waging war with Communistterrorists and it was not till 1959 that the state ofemergency was lifted. For another, some Malayanmalariologists , for example Sandosham (1962) werenot convinced that eradication campaigns successfulin certain other countries would necessarily meetwith success in Malaya.

It was the discovery by Paul Muller of Switzerlandin 1939 of the insecticidal action of DDT and its useduring the Second. World War that revolutionisedour views on malaria control. The residual insecticidesproved to be the most reliable, feasible and

economical method for the interruption oftransmission. Greece was one of the countries whereuse of DDT had decreased the vector population andmalaria had disappeared. War broke out in Korea inwhich the Americans were involved and the Greekscould not afford the increased cost of DDT andequipment. They decided to stop spraying certainplaces. The anopheline vectors returned in theseareas in numbers and the authorities kept theirfingers crossed expecting a return of malaria. It didnot happen. What had happened was that the periodof spraying had interrupted transmission and thedisease itself being self-limiting (relapses usually lasttwo or three years) had died out.

From this spectacular results of DDT spraying,grew the idea that a few years of intensive andthorough spraying of residual insectives on thewalls of the inside of houses would eradicate the

disease from a locality. The World HealthOrganisation thus started a worldwide programmeand began coordinating activities and the provisionof technical assistance.

Our neighbouring countries like Sri Lanka,Philippines and Pakistan had started their campaignsearly but had their setbacks: Sri Lanka for instancehad almost achieved eradication when there was aresurgence in 1954. Once again they were on thebrink of total victory in 1962 but could not preventmalaria from returning in epidemic proportions(Harrison 1978).

In spite of this, Malaya officially launched itsMalaria Eradication Programme in 1967 and in1982, a third of the country was still in the attackphase, more than 11,500 cases having been recordedin that year. Instead of the estimated costs of $85million to completely eradicate the disease, we havespent $120 million with no eradication in sight.

The World Health Organisation itself has realisedthat global eradication of malaria is not feasible andhas advocated a (flexible' malaria control programmeso that each country can develop its own long-termplan within its overall health plans and work towardsits own goals according to its means.

THE FUTURE

There still remain many problems in malariathat require elucidation. the differentiation of thestrains of the malaria parasites of man and the sortingout of the sibling species of Anopheles and thespecies complexes have to be carried out. A study ofthe genetic organisation and the manner in whichthe genetic factors are inherited are indicated.Enzyme electrophoresis and the biochemicalcharacteristics of DNA may prove to be of value.

More electron microscopic studies of the innerstructure of all stages of the malaria parasites isnecessary. Newer drugs have to be synthesised andchemotherapeutic tests have to be carried out.Further tests have to be made before mephloquinecan be safely put on the market because of its value

19

for the treatment of falciparum malaria resistant.to other drugs.

Work towards the development of a vaccine orvaccines against malada should be extended. Trager 'scontinuous in vitro cultures of P. falciparum haveto be conrinued as it may lead to the developmentof vaccine against this dangerous species. The valueof 'Qing Ho Su ' a drug extracted in China from amedicinal herb has yet to be established.Immunological reagents and techniques have to bestandardised to allow valid comparison of the resultsobtained by different workers in different areas andcountries. Vaccines to form T. cell in macrophagesare desirable. The programme to raise the livingstandards and the educational level of the peopleshould be continued.

The bibliography of malaria is large and thefollowing list of selected references concertrateson those of the very early workers and those relatedto Malaya.

REFERENCES

Bruce-Chwatt L J. 1980 Essential Malariology. London:William Heinmann Medical Books Ltd.

Coatney G A, Collins W E, Warren McW 1971 and ContactP G. The primate malaria. US Department Health EducationWelfare.

Field J W, Shutte P G. 1956 The microscopic diagnosis ofhuman malaria - II Kuala Lumpur: Government Printers.

Garnham P C C. 1966 Malaria parasites and other baemos­poridia. Oxford: Blackwell Science Publication.

Harrison G. 1978 Mosquitoes, malaria and man. London:John Murray.

Institute for Medical Research, Kuala Lumpur 1901-1976.Petaling Jaya: P. K. S. Publishers.

•Pampana E Y.. 1969 A textbook of malaria eradication2nd eetOxford University Press. London.

Peters' W. 1970 Cbemotberapby and drug resistance inMalaria Academy Press London and New York.

Reid J A. 1968 Anopheline mosquitoes of Malaya andBorneo. Stud Inst Med Res Malaysia; 310.

Ross Ronald. 1910 The prevention of malaria. John Murray.London.'

Sandosham A A. 1967 Non-human malaria parasites andtheir vectors in Malaya Protozoology 11: 149-164.

Sandosham A A, Thomas V. 1983; Malariology with specialreference to Malaya 2nd ed. Singapore University. Singapore.

Scott H H. 1939 A history of Tropical medicine. EdwardArnold, London.

Watson Malcolm. 1921 The prevention of malaria in theFederated Malaya States. John Murray, London.

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