Laboratory rearing of Theileria annulata-free Hyalomma anatolicum anatolicum ticks

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  • Laboratory rearing of Theileria annulata-free Hyalommaanatolicum anatolicum ticks

    S. Ghosh P. Azhahianambi

    Received: 12 March 2007 / Accepted: 13 August 2007 / Published online: 13 September 2007 Springer Science+Business Media B.V. 2007

    Abstract Hyalomma anatolicum anatolicum is a three-host tick which transmits Thei-leria annulata infection in Indian cattle. Laboratory rearing of ixodid ticks is an essentialrequirement of any laboratory engaged with research on ticks and tick borne diseases. The

    Entomology laboratory of Indian Veterinary Research Institute is fully equipped with all

    the facilities and skilled manpower to maintain a homogenous H. a. anatolicum populationthroughout the year. The continuous supply of eggs, larvae and adults of H. a. anatolicumis maintained to meet out the demand of different experiments viz., preparation of tick

    antigens for immunization of animals, experimental challenge, isolation of genomic DNA

    and RNA. Maintenance of a H. a. anatolicum colony free of T. annulata infection isimperative for the experimental challenge infestation on cross-bred (Bos indicus B. taurus) calves, in order to prevent the transmission of T. annulata infection to theexperimental animals. A system has been developed in the laboratory in which the larvae

    of H. a. anatolicum were fed on New Zealand white rabbits and the dropped fed nymphsmolted to adults are fed on cross-bred calves free of T. annulata infection. This syntheticcycle prevents the transstadial transmission of T. annulata as the rabbits are unsusceptibleto T. annulata infection and only the adults were fed on cross-bred animals. Moreover,absence of transovarial transmission of T. annulata prevents the chance of carry overinfection to experimental animals in the next cycle.

    Keywords Hyalomma anatolicum anatolicum Rearing of Theileria annulata free tick rabbit-cattle cycle

    Declaration: The experiments have been conducted in accordance with the approved guidelines ofCommittee for the Purpose of Control and Supervision of Experimentation on Animals (CPCSEA). Besides,the institute animal ethics committee continuously monitored the animal experimentation.

    S. Ghosh (&) P. AzhahianambiEntomology Laboratory, Division of Parasitology, Indian Veterinary Research Institute, Izatnagar, UP243122, Indiae-mail: sghoshp@yahoo.co.in

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    Exp Appl Acarol (2007) 43:137146DOI 10.1007/s10493-007-9100-3

  • Introduction

    As per the last compilation reports on tick species of India, approximately 106 tick species

    belonging to two families of Ixodidae and Argasidae are reported to infest domestic, wild

    and game animals (Geevarghese et al. 1997). Amongst the reported tick species,

    Hyalomma anatolicum anatolicum has been considered as one of the most widely dis-tributed tick species infesting cattle, buffalo, sheep and goat and transmitting Theileriaannulata, T. buffeli, T. lestocardi (T. hirci) (Ghosh et al. 2006). The predicted distributionof bovine tropical theileriosis in India and cattle and buffalo population at risk is well

    documented (Minjauw and Mc Leod 2003). As per their estimation the cost of control of

    theileriosis including the cost of control of ticks in India is about 441.5 million US$ per

    annum. Beside the vectorial potential of the tick species, the significant direct effect of

    ticks on livestock production (Biswas 2003) necessitated to develop methods to control the

    tick species in an environmental friendly manner.

    Under the national priority programme, the Division of Parasitology of the Indian

    Veterinary Research Institute is continuously working on development of immunopro-

    phylactic measures against the targeted tick species and the parasite, Theileria annualata(Singh and Ghosh 2003; Das et al. 2005; Ghosh et al. 2005). Continuous supply of

    T. annulata-free stages of H. a. anatolicum is one of the mandatory requirements for thedifferent types of experiments conducted for the priority programme. We have previously

    tried a cattle system for the generation of a tick colony but this strategy was not feasible.

    Subsequently, a different strategy was designed and was found effective. The entire

    strategy along with the life cycle data generated during the last 10 years is discussed.

    Materials and methods

    Animal

    Healthy New Zealand white rabbits of 1 year old and 1.52 kg in weight were used for

    feeding of ticks. The rabbits were maintained in clean disinfected rabbit cages of ca. 5 3.8 3.6 cm in size. Food and water were given ad libitum as per the ration developed bythe Laboratory Animal Research section of the institute. For raising good number of tick

    stages for different type of experiments and to avoid stress on animals, 68 rabbits were

    maintained simultaneously. Normally, two rabbits were utilized for each feeding cycle.

    After each feeding cycle, the animals were kept free for at last 20 days1 month.

    For feeding on large animals, cross-bred male calves of 610 months old and more than

    60 kg in weight, were maintained from the initial stage of birth in the tick and fly proof

    shed of the division of Parasitology. Each animal was kept in well-ventilated shed with

    slatted floor. The size of the individual shed was ca. 2.4 2.3 m (as per the recommen-dation of CPCSEA). The animals were examined regularly to maintain the disease free

    condition. To keep the animals stress free, 56 animals were maintained simultaneously

    and 23 animals were used for each feeding cycle. After each feeding cycle, the animals

    were kept free for 1520 days. To protect the animals from natural tick infestation, the

    animals were fed with dry fodder and water ad libitum. During winter (the outside tem-

    perature of the animal shed is going below 4C) the temperature of animal rooms weremaintained using room heater. The T. annulata/Babesia bigemina free status of the calveswere ascertained by periodical examination of Giemsa stained blood smears.

    138 Exp Appl Acarol (2007) 43:137146

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  • Ear bag for rabbit and cattle

    Ear bags for rabbit (7 10 cm) and for cattle (13 17 cm) were fabricated using mouslincloth. Stitching of bags was done meticulously so that the tick stages cannot come out from

    the bag. The typical design of the tick-feeding bag is given in Fig. 1a, b.

    Head collar

    For feeding on rabbits, head collars of the diameter of ca. 22 cm were used. The centre hole

    (for putting the collar on neck) was of ca. 6.5 cm in diameter for keeping the tick feeding

    bags undamaged on ear and also allow rabbit to take food and water easily.

    Collection of ticks from the field (Izatnagar)

    The engorged H. a. anatolicum ticks were collected from the resting places of cattle in andaround the institute, Izatnagar, UP, India. Collections were made from the cracks and

    Fig. 1 (a) Showing tick feeding bag for rabbit system; (b) showing tick feeding bag for cattle system

    Exp Appl Acarol (2007) 43:137146 139

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  • crevices with the help of forceps. Collection of engorged H. a. anatolicum from the animalshed is advantageous over the flag dragging method to collect the questing larvae as it is

    easier to identify the ticks at the adult stage and it does not require any lint flag.

    The collected ticks were identified as H. a. anatolicum by morphological key given bySen and Fletcher (1962).

    Rearing of collected ticks

    After proper identification, the fully engorged adults collected from the field were rinsed in

    distilled water and placed on filter paper kept inside the tick rearing glass tubes (5 cm in

    height and 2.5 cm in diameter) covered with mouslin cloth with the help of rubber band.

    Each vial bore a label bearing the name of the species and the date of recovery. The glass

    tubes were kept in desiccators where 85% relative humidity (RH) was maintained. The

    desiccators were kept at 28C or at 1820C for oviposition.

    Egg hatching

    After completion of the oviposition, the dead female H. a. anatolicum were removed fromthe glass tubes in order to avoid the fungal growth on the dead ticks and subsequent

    contamination of the eggs. The freshly laid eggs were kept at two different temperatures of

    1820C and 28C with 85% RH.

    Feeding of H. a. anatolicum larvae on rabbits

    Larvae were fed on New Zealand white rabbits. Before releasing ticks on animals, the ear

    pinnas were shaved without damaging the skin. For each feeding cycle, eggs laid by one

    tick were divided into two parts and were kept in separate tubes. The larvae hatched in each

    tube were used for each rabbit. Before releasing on rabbits the larvae were transferred from

    the glass tube to ear bags. The bags along with larvae were inserted into the ear pinna and

    the threads were gently tightened around the base of the ear pinna. Care should be exer-

    cised in such a way not to tight the rope around the base of the pinna as it might lead to the

    formation of edema around the pinna. The optimum tying of the bags with ear pinna

    required some expertise and experience in handling of animals for tick feeding. After

    releasing the tick larvae, the animals were checked daily twice, once in the morning and

    again in the evening to avoid the loss of tick stages. It was observed that when H. a.anatolicum larvae feeds on rabbits it has a two-host life cycle. After feeding, the engorgedlarvae are remaining on rabbit to moult into unfed nymphs, which then attach and engorge.

    The engorged nymphs were collected. In contrast, when the larvae were fed on cattle or

    gerbils it has a three-host life cycle and engorged larvae detach naturally and moult to

    unfed nymphs whilst off the host.

    Rearing of nymphs

    For moulting to next stage of development, freshly collected engorged nymphs were

    thoroughly cleaned before placing in tick rearing glass vials. The engorged nymphs were

    140 Exp Appl Acarol (2007) 43:137146

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  • kept in-group of 50 in each vial. The tube containing engorged nymphs were kept at two

    different temperatures and in 85% RH for moulting. The moulting pattern was recorded

    daily.

    Feeding of H. a. anatolicum adults on cattle

    The freshly hatched adults were kept unfed for 7 days before release on disease free male

    cross-bred calves. Before releasing the unfed adults, the ear pinnas were shaved smoothly

    for ease of attachment of ticks. For each infestation, 5070 unfed adults (males and females

    together) were taken in each ear bag and the bag was tied with the base of ear pinna.

    Extreme care was taken to avoid the formation of odema due to improper tying of bag with

    ear pinna. Usually the adults were released in the morning hours of the day and were

    closely observed for 24 h. During the initial stage of tick attachment (up to 12 h of release)

    the animals suffered from irritation and try to remove the tick-feeding bag. The ear bags

    were checked daily, collected the fed adults, cleaned, weighed, labelled and kept singly in

    the glass tube and were kept in the above mentioned temperatures and 85% RH for

    oviposition.

    Control of temperature and humidity

    The tick colonies were maintained in dessicators which were kept at 1820C and at 28Cin incubator. Except when the light was switched on for observation, the interior of the

    incubator was constantly kept dark. The humidity was maintained by keeping a 10%

    solution of KOH at the base of the desiccators (Solomon 1951). The condition provided a

    RH between 85% at 28C temperature.

    Collection of data

    The tick stages are maintained for more than 10 years in the Entomology Laboratory,

    Division of Parasitology, Indian Veterinary Research Institute employing the above-

    mentioned strategy to generate a homogenous colony. The data collected during this long

    period were analyzed and the mean data were presented for each and every parameter. All

    the tick feeding data were generated under the strict supervision of trained and experienced

    scientific and technical staff.

    Results

    Identification of tick species

    The collected ticks were identified as H. a. anatolicum. The females were identified by thepossession of hexagonal basis capitulum; capitulum short and palps broad; presence of

    knob like genital operculum which is circular in outline; scutum is usually longer than wide

    with a narrowly rounded posterior margin, with punctuation in central field and in scapular

    areas; the cervical fields are shallower with parallel sides.

    Exp Appl Acarol (2007) 43:137146 141

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  • The males were identified by the following descriptions: small elongated body; scutum

    punctuated with distinct lateral grooves; eyes spherical and orbital; basis capitulum sub

    triangular or broadly hexagonal dorsally; elongate adanal shields; subanal shields situated

    on the axis of adanal shields.

    Oviposition of engorged H. a. anatolicum

    The pre-oviposition period of the laboratory bred adult ticks varied with the temperature. If

    the ticks were kept at 1820C and 85% RH, the pre-oviposition period ranged between 25and 62 days (Mean = 38.4 days). However, at a constant temperature of 28C and RH85%, the pre-oviposition period ranged between 10 and 12.2 days (Mean = 6.4 days).

    The oviposition period was also varied with the temperature. At a temperature of 18

    20C and RH of 85% the oviposition period ranged from 25 to 38 days (Mean = 30.4days). While at 28C and 85% RH the oviposition period ranged between 18 and 22.4 days(Mean = 21.8 days). The rate of oviposition attained the peak between 6 and 11 days when

    the ticks were maintained at 1820C, whereas, the pattern of oviposition was completelydifferent when the ticks were maintained at 28C. Within four days, the egg laying reachedat peak and continued for another 2448 h. This could be attributed to the higher rate of

    digestion and absorption of blood at higher temperature. There was a linear relationship

    between the egg masses and the weight of the engorged adults. After oviposition, the

    females are dying within 17 days (Mean = 4.2 days) at 1820C, whereas it was 16 days (Mean = 3.4 days) at 28C.

    Hatching of eggs

    The incubation period of the freshly laid eggs varied between 50 and 60 days (Mean =

    57.9 days) when maintained at 1820C, while at 28C, the incubation period was 2028 days (Mean = 21.7 days). Hatched larvae were ready to feed on animals at approxi-

    mately 67 days after hatching.

    Feeding of H. a. anatolicum larvae on rabbits

    The larvae attached to the body of the rabbits usually within 1836 h of release. A

    significantly high percentage of fed larvae did not drop off after engorgement and molted

    to nymphs and reattached on the same host, thus maintaining two-host pattern of feeding.

    In all the experiments, not more than 6065% larvae succeeded in feeding on rabbit host.

    Among the successful larvae, more than 97% were recovered as fed nymphs and 2.52.8%

    dropped as fed larvae. The fed nymphs started dropping after 13th16th day (Mean = 14th

    day) and continued for 56 days. The general pattern of dropping of fed nymphs was

    nocturnal.

    Rearing of nymphs for moulting

    The engorged nymphs stopped movement after 67 days of keeping in the rearing tubes

    and moulted to next stage after 1315 days (Mean = 14 days) of incubation. The complete

    142 Exp Appl Acarol (2007) 43:13...

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