Helminth infections (see Table 1) are major causes of mor-bidity in all age groups in the developing world. Around a

quarter of the world population is infected with soil-transmit-ted helminths like hookworm and Ascaris, and nearly 250 mil-lion with schistosomiasis. In the developed world, due toimprovements in hygiene and food safety, local transmissionof infection is infrequent, though infections such asEnterobius remain common. However, with the increase ininternational travel, migration and more adventurous behav-iour, unusual helminth infections may be encountered any-where.

Worldwide it is nematodes, or roundworms, that causethe bulk of infection. The soil-transmitted intestinal helminthsAscaris, hookworm, Trichuris and Strongyloides are good pop-ulation-level markers of poor hygiene and general deprivation,and cause growth and educational impairment in childrenand anaemia in pregnancy. Filaria are endemic in over 70countries and infect about 120 million worldwide but are rarein travellers. Tissue helminths, such as Trichinella, maybecome more frequent with increasing travel and dietaryadventure – the same is true for the lung and intestinal trema-todes, or flukes.

Schistosomiasis is a well-recognised infection in migrantsand travellers from sub-Saharan Africa. The tapeworms, or ces-todes, are found worldwide and again depend on dietary expo-sure for transmission. Neurocysticercosis, now recognised asa leading cause of epilepsy in the developing world, is beingincreasingly recognised in migrants and travellers.

In general helminths are unable to complete their life-cyclein humans, and the major determinant of pathology is thenumber of worms initially infecting the host, the worm load.The majority of UK-born individuals with worm infections willbe asymptomatic due to short-lived exposure and relativelylight infection loads. Often they will only discover infection bychance on routine screening or on passing a worm in thestool.

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Diagnosis and recommendedtreatment of helminth infectionsAllifia Abbas BSc, MRCP, Paul Wade MSc, BPharm andWilliam Newsholme MSc, FRCP, DTM&H

A number of worm infections are seen in theUK, often in migrants from tropical coun-tries, and it is essential to take a travel his-tory. Our Drug review discusses the featuresof the most common infections and detailscurrently recommended treatments.

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Figure 1. Adult hookworms can live in the small gut for years and can cause aniron-deficiency anaemia in patient groups such as pregnant women

Classic helminth disease will be seen more commonly inmigrants, those visiting families overseas, and individuals suchas aid-workers who have a more prolonged exposure. Failure toobtain a travel history may mean that helminth infection is notconsidered.

Epidemiological data in the UK are limited and difficult tointerpret due to poor levels of reporting, particularly of travelhistory, to Public Health England (PHE). However, screening ofantenatal clinic attendees suggests around 10 per cent ofwomen from the Indian subcontinent may be carrying intestinalhelminths, with up to 45 per cent of Bangladeshi women har-bouring infection, the majority being hookworm and Trichuris.

It should be borne in mind that around 12 per cent of theUK population was born overseas (data from 2010) and that20 per cent of all UK travel was to visit friends and relatives(VFR) overseas, with around 790 000 journeys to the Indiansubcontinent and 400 000 to sub-Saharan Africa. As many as43 per cent of all asylum seekers and 8 per cent of universitystudents are of sub-Saharan African origin and all thesegroups potentially are reservoirs of imported infection.

The gut helminthsMost infections in the UK are in migrants from tropical countries.The majority of individuals with gut helminths will be relativelyasymptomatic, though a variety of symptoms may be attributa-ble to the helminth infection (see Tables 2 and 3). Infection maybe discovered incidentally when investigating for other symp-toms. Eosinophilia is rare with cestode infection but is morecommonly seen in infection with trematodes and nematodes.

RoundwormsEnterobius vermicularis (threadworm, see Figure 2)This is the most common gut helminth in the UK, especiallyamong school-age children; childhood prevalence may be up to50 per cent. It may be seen in any socioeconomic or ethnicgroup. Infection is by accidental ingestion of eggs, which maypersist for several weeks in the environment allowing ongoingtransmission within families and institutions. Adult femaleworms migrate to the anal margin to deposit eggs, giving thecharacteristic nocturnal perianal itch. Ectopic worm migrationmay give rise to vaginal infection, which may be associated with

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recurrent urinary tract infections (UTIs). In some studies up to36 per cent of young females with UTI have been found to beco-infected with threadworm.

Reinfection from fingers and contaminated objects, suchas bedding, is easy. A third of infections are asymptomatic andblood tests are almost always normal.

Relapsing infection may require monthly treatment to breakthe cycle of reinfection. Topical malathion may reduce perianalitch, but must be used with care because it may also cause localirritation.

Ascaris lumbricoides (common roundworm, see Figure 3)Over one billion people and up to 50 per cent of school-age chil-dren are thought to be infected with Ascaris worldwide, with ahigher prevalence in warmer countries. Around 60 cases arereported to PHE annually, the majority appearing to be con-tracted in the Indian subcontinent, but an accurate travel historyis often not reported. Infection is by accidental ingestion of eggs,with a larval migratory phase through the lungs that may causea transient pneumonitis.

Infection is often discovered when adult worms are passedper rectum or vomited. Worms are 15–35cm in length and whiteto brown in colour, looking not unlike earthworms. Large wormburdens may cause malabsorption syndromes, but the mostsevere disease manifestations occur when worms migrate intothe biliary tree causing cholangitis, or become caught in theappendix or plug a section of bowel causing obstruction, intus-susception or volvulus.

Trichuris trichiura (whipworm)Up to 800 million individuals, mostly school-age children, areinfected worldwide, with transmission by accidental ingestionof ova. Less than 50 cases per year are reported to PHE, mostlyin individuals from the Indian subcontinent, sub-Saharan Africaand South-east Asia; indigenous infection is uncommon.Infection is often asymptomatic but may cause abdominalcramps, diarrhoea, per rectal blood loss, rectal prolapse andmalabsorption with heavy infestations.

Strongyloides stercoralisThough mostly confined to the wet tropics and subtropics, infec-tion is found worldwide. About 40 cases per annum are reportedto PHE, roughly two-thirds in migrants and one-third in travellers.Initial infection is by larval skin penetration from faecally con-taminated soil. Infectious larvae are also passed in the stooland may penetrate perianal skin, so allowing persistent infectionof a host despite no further exposure to contaminated soil. Forthis reason disease may become evident many years after leav-ing an endemic area and may only become problematic in olderage or with intercurrent immunosuppression.

Larval migration can cause both a pulmonary eosinophiliasyndrome and transient cutaneous urticarial eruptions (larva cur-rens). Most infection is asymptomatic. Larger infection loads maycause diarrhoea, protein-losing enteropathy and oedema, whilein the immunocompromised a potentially fatal hyper infection syn-drome associated with Gram-negative sepsis may occur.

Ancylostoma spp. and Necator spp. (hookworm)Hookworm (see Figure 1) is endemic in the tropics and subtrop-ics, infecting about one billion individuals worldwide. About 30cases per annum are reported to PHE. Indigenous infection inthe UK is rare and the majority of cases seem to be acquired insub-Saharan Africa and south Asia. Infection is acquired by lar-val skin penetration from contact with faecally contaminatedsoil, causing a localised itchy rash (‘ground itch’). Infection bynonhuman hookworms can cause a persistent, intensely itchyserpiginous rash, known as cutaneous larva migrans. Migrationthrough the lungs can cause a more persistent pneumoniticLöeffler’s syndrome than that seen with Ascaris, sometimeslasting several months.

Adult worms live in the small gut for up to a decade, takingblood meals of up to 0.25g per day, and can produce an iron-deficiency anaemia in three to five months in populations suchas pregnant women. Hypoproteinaemic states, diarrhoea andabdominal pain may also be seen. Hookworm anaemia causesover 65 000 deaths per annum worldwide.

Trichinella spiralis (roundworm)Trichinella is acquired from ingestion of infected pork or boar.There has been no domestic infection in the UK since 1969, butsporadic outbreaks occur from imported foodstuffs, especially

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Table 1. Classification of the principal helminths

Nematodes Trematodes Cestodes(roundworms) (flukes) (tapeworms)

Ascaris lumbricoides Schistosoma Taenia saginataNecator americanus, mansoni (stool) (beef)Ancylostoma Schistosoma Taenia solium (pork)duodenale (hookworm) haematobium (urine) Hymenolepis nanaTrichuris trichiura Fasciola hepatica Diphyllobothrium(whipworm) (liver fluke) latumEnterobius vermicularis(threadworm, pinworm)Strongyloides stercoralisTrichinella spiralis

Table 2. Signs and symptoms of infection associated with gastro -intestinal helminths

Gastrointestinal Systemic

epigastric pain anaemiadiarrhoea (see Table 3) eosinophiliamalabsorption states feverappendicitis cardiac failureright iliac fossa pain/mass bronchospasmpruritus ani pneumonitisrectal prolapse septicaemiabowel obstruction/volvulus epilepsybiliary obstruction/ dermatologicalcholangitis manifestations, eg urticaria

poorly cured pork sausages. Only a small proportion of casesbecome symptomatic. Disease initially manifests with a feverand diarrhoea at the time of gut invasion. Several weeks latertissue invasion causing fever, myalgia, eosinophilia and perior-bital oedema may be seen. Sometimes myocardial, pulmonaryand CNS disease can occur, which may be fatal.

Tapeworms (Taenia spp, Hymenolepis, see Figure 4)Tapeworm infection is seen worldwide, wherever cattle or pigshave access to human faeces and where food controls are lax.Over 100 cases per annum are reported to PHE, the majoritybeing T. saginata, the beef tapeworm.

Beef tapeworms are up to 5m in length and usually asymp-tomatic, coming to light when worm segments are passed inthe faeces.

Pork tapeworm is also usually relatively asymptomatic andrarely reported in the UK. Accidental ingestion of T. soliumeggs from infected faeces can give rise to cysticercosis, withthe development of painless cutaneous and muscle nodules,myocarditis and CNS cysts. These remain asymptomaticunless causing blockage to cerebrospinal fluid flow or by caus-ing localised inflammation when the cyst dies, which can pre-cipitate epileptic seizures. Management of neurocysticercosis

is difficult and suspected cases should be referred to regionalinfectious diseases or neurology units for investigation andtreatment.

The dwarf tapeworm, Hymenolepis nana, may be associatedwith diarrhoea and vague neurological syndromes includingheadaches, dizziness and sleep disturbance in children.Infection is found worldwide and it is probably the commonesttapeworm in the USA. Ten to twenty cases per year are reportedin the UK, the majority with a travel history to the Indian sub-continent.

Bloodstream and tissue helminthsIt is uncommon for UK-based travellers to have symptomatic tis-sue helminths, though migrants may present with unusualsymptom complexes due to schistosomal or filarial disease.

Schistosomiasis (see Figure 5)Schistosomiasis affects over 200 million worldwide and iscaused by a bloodstream fluke. It is acquired through larval skinpenetration while in contaminated fresh water and there are avariety of syndromes associated with infection.

During the early phase of larval migration fever, eosinophilia,urticaria and myalgia may be seen. This is named Katayamasyndrome and is part of the differential diagnosis of acute feverin those returning from endemic areas. It is more likely to beseen in tourists than VFR. S. mansoni may cause persistentbloody diarrhoea in migrants and travellers from sub-SaharanAfrica.

In the UK a peak of about 200 cases per year was seen inthe early 1990s, though this has fallen to less than a 100 peryear currently. Between 2003 and 2005, 116 cases of S.haematobium, 43 S. mansoni and 44 unspecified cases werereported to the HPA. A travel history was available in about 30per cent of cases, of which more than 80 per cent had travelledto sub-Saharan Africa, about three-quarters of cases were inmales and 80 per cent in those aged 15–39 years.

Filarial diseaseFilarial transmission is inefficient and it is unusual for thosewithout prolonged exposure to the vector species to acquire sig-nificant infection. Only 85 cases of filarial disease were reportedin the UK between 1999 and 2008, 36 being a tissue filaria,Loa loa, five cases of Onchocerca and 23 of Mansonella.Classical lymphatic filariasis, with lymphoedema and elephan-tiasis, is very rarely reported in the UK, with only six casesreported in this time.

InvestigationMost helminths are acquired oversees, and the importanceof a carefully taken travel history cannot be overemphasised.The majority of patients with gut helminths will be either rel-atively asymptomatic or will present having passed a wholeworm or worm segment. Identification of worms can beundertaken by local microbiology laboratories or by referencecentres. Individuals with gastrointestinal symptoms or con-cerns following travel can be initially screened by stool exam-

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Table 3. Gastrointestinal helminths and associated diarrhoea

Not associated with Possibly causing Definitely causing diarrhoea diarrhoea diarrhoea

Enterobius vermicularis hookworm species Trichuris trichiuraAscaris lumbricoides Hymenolepis nana StrongyloidesTaenia species Diphyllobothrium stercoralis

latum SchistosomaspeciesTrichinella spiralis

Figure 2. Threadworm infection is not associated with diarrhoea

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ination for ova, cysts and parasites, and a full blood countfor eosinophilia.

Enterobius can be identified using the various commerciallyavailable variants of the Sellotape test to provide perianal sam-pling for ova. Proctoscopy may be of use in identifying Trichuris.Stool microscopy and eosinophil count may not be sufficientlysensitive for screening for infections such as Strongyloides, andserological tests may be needed. Interpretation can be complexand their use is probably best discussed with local infectiousdiseases or microbiology departments. Evidence suggestive ofcysticercosis may be found on plain X-ray of the large musclegroups, showing calcified cysticerci, but investigation of neuro-cysticercosis is complex and should be undertaken by a spe-cialist centre.

Given the sometimes complex epidemiology and presenta-tion of the more obscure helminths, including schistosomiasis,it is often worth discussing cases with local infection servicesor referring patients to a specialist centre for formal assessmentand treatment.

Treatment (see Tables 4 and 5)When one individual in a family is found to be infected it maybe prudent to screen other members for infection, particularlyin cases such as threadworm. Patients should be advised aboutpersonal hygiene and care during food preparation, but also bere assured that, in general, transmission of most helminthswithin the home is difficult.

Drugs used in the treatment of helminths may be difficultto obtain and several are available on a named-patient basisonly. For exotic helminth infections, referral to an infectious dis-eases service will probably be necessary from the point of viewof accurate diagnosis, obtaining medication and for appropriatefollow-up.

Data on the use of all anthelmintic drugs during preg-nancy and breast-feeding are limited, so their use in thesesituations should be discussed with specialists. It is probablywiser in most situations to withhold treatment until the endof pregnancy.

Most anthelmintic drugs are not licensed for use in childrenunder two or have age- or weight-adjusted dosing regimens.

Single worm infections, such as Ascaris or Enterobius, canbe easily treated in the community. Mebendazole and piper-azine (Pripsen) are both available in the community and shouldbe used as first-line agents. Albendazole (named-patient only)is probably better tolerated and slightly more efficacious than

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Figure 3. Roundworm are 15–35cm in length and large worm burdens can cause malabsorption syndromes

Figure 4. Taenia saginata or beef tapeworm; worms are up to 5mlong and usually asymptomatic

Figure 5. Schistosome fluke; infection should always be referred to aspecialist centre

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mebendazole. With recurrent infection in families, multiple infec-tions or complex infections such as Strongyloides or schistoso-miasis, it is more appropriate to refer the patient to a specialistunit for treatment.

Benzimidazoles are toxic to nematode cytoskeletal elementsand to ova. Side-effects of mebendazole and albendazole areminimal and transient and include epigastric discomfort, nau-sea, headache, rash and urticaria. No drug interactions havebeen documented but cimetidine and steroids may increaseserum benzimidazole levels. Benzimidazoles may take severaldays to take effect, and with small worm burdens visible wormremnants may not be seen in the stool.

Piperazine causes helminth muscle paralysis, possibly bycompetitive antagonism of acetylcholine. It is contraindicatedin epilepsy as it may lower the seizure threshold. There is someevidence of neurotoxicity causing ataxia, myoclonus and hypo-tonia. Commoner side-effects are gastrointestinal upset andurticaria. Piperazine may interact with phenothiazines, increas-ing extrapyramidal effects.

Ivermectin (named-patient only) causes ion channel-medi-ated helminth muscle paralysis. Side-effects are unusual andinclude pruritus, oedema, rash, fever, headache and tender lym-

phadenopathy. Rarely orthostatic hypotension may occur. Thereare no documented drug interactions.

Praziquantel (named-patient only) causes helminth muscleparalysis and membrane damage. It may cause abdominal dis-comfort, dizziness and somnolence, which is exacerbated byalcohol. Cimetidine may increase serum levels and chloroquinecan reduce bioavailability.

Niclosamide (named-patient only) causes adult tapewormmuscle paralysis. There are no documented drug interactionsand only minimal side-effects are reported with this drug.

Levamisole (named-patient only) causes helminth muscleparalysis. Nausea, gastrointestinal disturbance and mild neu-rological symptoms are reported.

Nitazoxanide is a relatively new anthelmintic agent, currentlynot licensed in the UK. Its mode of action is via enzyme block-ade in parasite anaerobic metabolism. There are increasingdata for its utility in tapeworm, Ascaris and Enterobius infec-tions, with less clear data for use in Strongyloides and Fasciola(as well as Giardia and cryptosporidium) Side-effects includeabdominal pain, nausea and headache. There are little data onuse in pregnancy and in renal or liver impairment and the drugshould be used with caution in these settings.

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All drugs available on a named-patient basis can be orderedvia IDIS World Medicines with about a two-week waiting time.

ConclusionThe majority of helminth infections in the UK are relativelyasymptomatic; however, they may be of relevance, particularlyin migrant populations. Most can be relatively easily diagnosedby local laboratory services. Schistosomiasis and neurocysticer-cosis should always be referred to a specialist centre, given theirpossible complications.

Management may be better carried out by specialist unitsfor the more complex diseases for a variety of reasons, not leastthat drugs may be difficult to obtain in the community.

References Burkhart CN, et al. Assessment of frequency, transmission and genito -urinary complications of enterobiasis (pinworms). Int J Derm2005;44:837–40.Migrant health. Infectious diseases in non-UK born populations inEngland, Wales and Northern Ireland. A baseline report – 2006. HPA,2006.Migrant health: Infectious diseases in non-UK born populations in theUK. An update to the baseline report, 2011. HPA, 2011.Checkley AM, et al. J Infect 2010;60:1–20.PHE patient advice sheet on threadworm: available at: www.hpa.org.uk/Publications/InfectiousDiseases/Factsheets/factThreadWorms/.

Declaration of interestsNone to declare.

Dr Abbas is a general medical registrar, Paul Wade is a consultant pharmacist, infectious diseases, and DrNewsholme is a consultant in infectious diseases at Guy’sand St Thomas’ NHS Foundation Trust, LondonTable 5. Recommended first-line treatments

Organism Recommended first-linetreatment

Ascaris, Trichuris, mebendazole or albendazoleEnterobius, hookwormStrongyloides albendazole or ivermectinTrichinella albendazolecutaneous larva migrans albendazole or ivermectinschistosomiasis praziquanteltapeworm niclosamide or praziquantel

Table 4. Drugs used in the treatment of helminth infections

Drug Organism Adult dosage (BNF 66)

Mebendazole (OTC) Ascaris, Trichuris, hookworm 500mg single dose or 100mg twice daily for 3 days Enterobius 100mg single dose; repeat at 2 weeks if recurrent, also

consider treating whole family

Albendazole Ascaris, Enterobius, Trichuris, hookworm 400mg single dosecutaneous larva migrans 400mg once daily for 3–5 daysStrongyloides 400mg twice daily for 3 days and consider redosing after

3 weeksTrichinella 5mg/kg daily for 1 week

Piperazine (OTC) Ascaris 4g single dose, repeat monthly up to 3m if reinfection riskEnterobius 4g single dose, repeated at 2 weeks

Ivermectin Strongyloides, cutaneous larva migrans 200µg/kg once daily for 2 days

Niclosamide tapeworm 2g single dose

Praziquantel tapeworm 5–10mg/kg single doseHymenolepis nana 25mg/kg single dose schistosomiasis 20mg/kg, 2 doses, 4–6 hours apartS. japonicum 20mg/kg, 3 doses in one day

Levamisole Ascaris 120–150mg single dosehookworm 120–150mg single dose, repeat at 1 week if heavy

infestation

Nitazoxanide Ascaris, Enterobius, tapeworm including 500mg twice daily for 3 daysHymenolepis, Fasciola