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Thirty-seven high grade cattle were immunised against Corridor disease (Theileria parva lawrencei infection) on a farm with a history of heavy and often lethal theilerial challenge. Nineteen cattle were immunised by treating with two doses of long-acting oxytetracyclines given at 20 mg/kg on days 0 and 4 after sporozoite stabilate inoculation, while the other 18 were treated with naphthoquinone buparvaquone, given as a single dose of 2.5 mg/kg simultaneously with stabilate inoculation. All the cattle underwent subclinical theilerial reactions with all but two developing high antibody titres on the IFAT test against T. parva schizont antigen by day 35 after the immunisation. Both buparvaquone and long-acting oxytetracycline appeared equally effective in the immunisation. To date, 26 months later, only two cases of theileriosis parasitologically characteristic of T. p. parva have been reported in the immunised cattle. Following the two cases, investigations showed that when uninfected Rhipicephalus appendiculatus nymphal ticks were deliberately fed on healthy resident cattle on the farm, the resultant adult ticks transmitted acute and lethal theilerial infections to five out of five susceptible cattle. The resultant infections were parasitologically characteristic of T. p. parva infections. Furthermore, the monoclonal antibody profiles of schizont infected cell lines from these infections appeared to be characteristic of T. p. parva. It was thus concluded that resident cattle on the farm could be a potential source of T.p. parva infection which had broken through the immunity of T.p. lawrencei immunised cattle and could constitute a reservoir of theilerial infection for ticks and hence to susceptible stock on the farm.

Laboratory reared Ixodes scapularis proved to be an efficient vector of Babesia odocoilei Emerson and Wright between white-tailed deer (Odocoileus virginianus). Transtadial survival of the babesia occurred between nymph and adult stages of the tick, and the adult stage transmitted the babesia.

The parthenogenetic Haemaphysalis longicornis larvae engorged on cattle naturally infected with Theileria sergenti were reared at 24 degrees C. The resultant nymphal ticks were incubated at 37 degrees C to clear the effect of incubation on the development and maturation of sporozoites. The sporozoites in the salivary glands of the nymphal ticks exposed to 37 degrees C for 16 days were observed by the methyl green pyronin staining method. The ticks exposed to 37 degrees C were ground up in a mortar and the supernatant of the tick suspension in PBS was inoculated into cattle. The cattle showed parasitemia and specific antibody response 18 days after inoculation. Consequently, the parasites in the tick salivary glands became infective to cattle by incubating infected. H. longicornis nymphs at 37 degrees C.

For a period of one year Haemaphysalis longicornis ticks were collected in a pasture from vegetation by dragging flannel cloth and from soil samples at monthly intervals. Nymphal ticks were assessed for Theileria infection. Salivary glands were stained with methylgreen-pyronin and examined for parasite masses. Nymphal H. longicornis infected with Theileria sergenti were found in all samples during 12 months including the winter. After shortening the prefed period on rabbits to 24 hours, the parasite masses could be detected in the salivary glands of nymphs collected in the grazing season, from May to October, while no parasite masses were detected in other season. It was suggested that the environmental factors in the grazing season might influence on the maturation of parasites in the salivary glands of ticks.

In endemic regions, Peromyscus leucopus, the mouse reservoir of the Lyme disease spirochete (Borrelia burgdorferi) and the piroplasm causing human babesiosis (Babesia microti), is nearly universally infected with both agents. Paradoxically, spirochetal infection is nearly twice as prevalent as is babesial infection in populations of field-collected nymphal Ixodes dammini, the tick vector. In the laboratory, a similarly disproportionate rate of infection was observed among nymphal ticks, feeding as larvae, on either B. burgdorferi- or B. microti-infected mice. Ticks which fed on mice with concurrent spirochetal and babesial infections also exhibited twice the incidence of spirochetal infection over that of the piroplasm. These data suggest that the efficiency of acquisition and transstadial passage of B. burgdorferi and B. microti infection differ by a factor of two. This discrepancy may explain differences observed both in the prevalence of infection in ticks collected in the field, as well as the apparently greater risk of spirochetal infection to humans in endemic areas.

Two Bos taurus calves were made resistant to tick infestation by exposing them to approximately 500 rabbit-reared nymphs of Hyalomma anatolicum anatolicum twice at a 2-week interval. These two calves, together with a tick-susceptible control calf, were inoculated with a stabilate of Theileria annulata (Ankara). Patent infection resulted in all three calves. Seven-hundred and fifty gerbil-reared nymphs were then applied on each of these calves as well as another tick-susceptible calf that was Theileria free. This infestation was carried out on Day 8 post-inoculation. Ticks that dropped on Day 13 post-inoculation were examined to note the development of T. annulata in them and the histological changes that occurred in the gut and salivary glands. During the second phase of feeding, the gut epithelia of the ticks from the tick-resistant calves were less active. There were no notable differences in the characteristics of the developmental stages of T. annulata between the ticks from the tick-resistant calves and those from the susceptible calf. However, ticks from one calf that acquired a higher level of tick resistance were significantly less susceptible to infection by T. annulata. Bovine tick resistance therefore compromises the vector capacity of H. a. anatolicum and this may be of epidemiological significance in the endemic areas of tropical theileriosis.

Rhipicephalus appendiculatus nymphs were inoculated with fresh or cryopreserved blood containing Theileria parva piroplasms, or with cell culture grown stages of T parva. The use of fresh blood was successful. Cryopreserved blood containing dimethylsulphoxide (DMSO), killed most nymphs after inoculation: DMSO could be removed by slow dialysis, without destroying the infectivity of the blood. Attempts to infect ticks by inoculating cell culture grown stages of T parva failed, even when large numbers of merozoites were present in the inoculum.

The development of motile stages, called kinetes, from a stationary stage (regarded as zygote) has been followed in Theileria parva by means of electron miscroscopy. This process started after moult of the tick nymphs which had sucked on highly infected calves, i.e. about 20 days after repletion (a.r.) of the ticks. The transformation took place by formation of a growing protrusion (= anlage) into an inner, enlarging vacuole. During this process the limiting membrane of the enlarging vacuole serves as the outer membrane of the developing motile stage, whereas the two inner ones as well as the subpellicular microtubules are newly formed. This transformation proceeds rapidly, so that on the 25th day a.r. most of the kinetes have already left the gut cells and started penetration into the salivary gland cells. On the way to the salivary glands nuclear divisions occurred within the kinetes. The steps of the transformation described were compared to those in T. annulata and to ookinete formation in haemosporidia.

Gamogony of Theileria ovis Rodhain occurs within the gut of nymphs of the tick Rhipicephalus evertsi evertsi Neumann. After molting, spherical and ovoid parasites are found within the intestinal cells of the ticks. These stages are thought to be zygotes, because they undergo a transformation process leading ultimately (in 3 days) to the formation of a motile stage, the kinete, the fine structure of which is very similar to that of the ookinetes of the hemosporidia. The kinete leaves the gut cells of the tick and penetrates the salivary gland cells where it produces infective stages (the sporozoites). These stages may be transmitted to sheep during the next blood meal of the tick. The developmental processes of T. ovis are compared to those of Hemosporina.

Larval and nymphal Haemaphysalis bancrofti became infected with Theileria buffeli following the intraperitoneal inoculation of infected bovine blood into CBA mice on which they were feeding. Subsequent instars of fed ticks were released on calves and transmitted theileriosis at each of 10 attempts. Suspensions made from ticks moulted in vitro and then incubated for 4 days at 37 degrees C were also infective for calves inoculated subcutaneously. The findings provide a convenient method for infecting ticks with field isolates of Theileria.

A 2 hectare paddock on the Muguga Estate, Kiambu District of Kenya (altitude 2100 m) free of Theileria parva-infected ticks was seeded by applying Rhipicephalus appendiculatus nymphs to cattle infected with Theileria parva (Kiambu 4). It was estimated that over 50 000 engorged nymphs fell onto the pasture from 4 cattle with high parasitaemias during the cold season (June). Samples of these ticks were placed in plastic cylinders under the vegetation in the paddock and sexual stages of T. parva were detected in gut lumen smears in these samples up to 21 days after repletion. Zygotes were first observed to transform into kinetes on day 55 and parasites were first detected in salivary glands of adults on day 64. Moulting of the nymphs started on day 60 after repletion and was completed by day 87. Cattle introduced into the paddock showed their first infestation with adult R. appendiculatus on day 64 after repletion of the nymphs and the infestation level gradually increased. On day 76 after repletion, 17% of a sample of adult ticks infesting cattle showed salivary gland infections with T. parva and this increased to over 70% by day 150. From day 360 onwards, a decrease in both the percentage of ticks infected and the number of salivary gland acini infected/tick was noted. In addition, T. parva infections within the salivary glands required a longer period of feeding in the older ticks before they developed into sporozoites. Cycling of Theileria through ticks was prevented by the removal of female ticks before they completed repletion. Lethal challenge levels of T. parva for cattle existed in the paddock up to day 547 after repletion, after which introduced cattle showed no infection or only a sub-lethal infection. Cattle introduced into the paddock on day 808 after repletion showed no evidence of T. parva infection. The tick infestation of introduced cattle decreased markedly from day 368 and infestation had virtually ceased by day 808.

Amastigotes, sphaeromastigotes, epimastigotes and trypomastigotes of Trypanosoma theileri, Laveran, 1902 have been observed in the nymphs and adults of Hyalomma anatolicum anatolicum (Koch, 1844). There ticks were obtained from engorged larvae and nymphs collected from a cross-bred bull with detectable parasitaemia. Infection with T. theileri was established in two 6-8-month old cross-bred calves by subcutaneous inoculation of Trypanosomatid flagellates collected from ticks and by feeding of the infected ticks on the ears of these calves.

Ixodes dammini nymphs were examined for evidence of concurrent infection with Borrelia burgdorferi and Babesia microti. A total of 19 nymphs (18.6%) from Nantucket Island were simultaneously infected, as were 24 nymphs (8.2%) from Naushon Island. These observations are consistent with a common reservoir host for both I. dammini-transmitted pathogens.

During the feeding of larvae and nymphs of A. lahorensis haemorrhagic inflammation develops in the rabbit's skin. Lymphocytes and macrophages are the dominant cell elements in the reaction while during the feeding of nymphs eosinophilous leucocytes are observed in great number in the infiltrate. Around the oral parts of the tick an infiltration of collagenous fibres of the connective tissue is formed, which serves for a more firm attachment of the parasite, while beneath the proboscis a light band is formed from which the tick sucks the food substratum. By the end of the feeding of nymphs III in the place of skin affection a crust can be formed on account of the host's atrophied tissues, and in the integuments there are formed necrotic foci due to the hystolitic and toxic effect of the saliva.

Adult triatomine insects, Panstrongylus megistus, naturally infected with the protozoa, Trypanosoma cruzi, contained significantly more metacyclic trypomastigote forms in their digestive tracts than did P. megistus nymphs. Metacyclics were scarce in all stages of triatomines fed once on infected mammalian hosts and subsequently starved. In contrast, triatomines fed repeatedly on infected mammalian hosts developed prolific T. cruzi infections. Repeatedly fed adults contained 14 X more metacyclics than similarly fed nymphs. Nutritional factors appear to play a key role in regulating metacyclogenesis. Control campaigns designed to alter the age structure of populations of triatomines must take notice of the high transmission potential of the adult stage.

The development of Theileria velifera in the gut and the haemolymph of the tick vector Amblyomma variegatum is described. Between days three and eight after repletion various sexual stages are present in the gut of the nymphs. Zygotes were detected in the gut on day 14, while undifferentiated kinetes first appeared on day 15. In the haemolymph, differentiated kinetes were observed from day 16 after repletion onwards. Zygotes and kinetes were also found after the moult, in the adult tick, for a prolonged period of time. The results of this study show that the developmental stages of T. velifera in the gut and haemolymph are characteristic of the genus Theileria.

Developmental time and mortality in nymphs of the reduviid bugs Triatoma sordida (Stål), Triatoma pallidipennis (Stål) and Dipetalogaster maxima (Uhler) were studied in uninfected groups and in those infected with Blastocrithidia triatomae Cerisola et al. (Trypanosomatidae). In T.sordida and T.pallidipennis, major vectors of Chagas' disease in Brazil and Mexico respectively, infection with B.triatomae was associated with slight developmental retardations in the final instars, and increased mortality in the pre-adult instar. These effects were less evident in T.pallidipennis, but in this species a total infection rate of only 5-15% was achieved, compared with about 45% in T.sordida. In contrast, D.maxima was strongly affected by B.triatomae: nymphal development was retarded and complete mortality occurred in some groups exposed to infection, although not all bugs were infected.

The life-cycle of the nematode Rhabdochona phoxini, an intestinal parasite of the fish Phoxinus phoxinus, has been studied experimentally. The mayfly nymphs, Habrophlebia lauta Eaton and H. fusca (Curtis) were found to serve as experimental intermediate hosts. After the eggs of R. phoxini have been swallowed by the mayfly nymph, the toothed first-stage larvae of this parasite are released and penetrate through the intestinal wall into t-e body cavity of the mayfly. Before reaching the infective third stage, the larvae moult twice in the body of the invertebrate host (2 to 16 and20 to 36 days after infection at water temperatures of 13--15 degrees C). However, the development of the encysted infective larvae does not cease in the intermediate host and the larvae may undergo one more moult. One of two moults then occur in the intestine of the definitive host (Phoxinus phoxinus) (depending on the fact whether it was infected with third- or fourth-stage larvae) before the larvae attain the maturity. The development of R. phoxini in the definitive host lasts about two months.

The endogenous development of Theileria annulata in the vector tick--Hyalomma anatolicum anatolicum has been described. Parasites within and outside the erythrocytes were seen in the gut contents of larvae and nymphs immediately after their removal from the infected cattle but not after 24 hours. Two bodies resembling the intra-erythrocytic stage of the parasite, lying close to each other were seen near the gut epithelium of a larva on the 4th day of its dropping off the infected host. Neither multiplication nor union of the parasite resulting in zygote formation in the gut of the tick, was noticed. Next stage of the parasite was seen in the salivary glands of nymphs and adults. The pre-infective stage characterized by indistinct chromatin dots (nuclei) surrounded with cytoplasm was seen in alveolar cells of the salivary glands of nymphs and adult ticks from the first to the third day of their feeding of the host. This stage progressed to the infective stage consisting of distinct chromatin particles (the infective particles) surrounded with cytoplasm in the salivary glands of nymphs and adult ticks after the second and first day, respectively of feeding on the host. The infective particles were also seen within ducts of the salivary glands.

An entomophagous wasp (Hunterellus hookeri Howard) parasitizes about a third of the host-seeking nymphal Ixodes dammini Spielman et al. ticks on Naushon Island in Massachusetts (U.S.A.) where the agents of Lyme disease (Borrelia burgdorferi Johnson et al.) and human babesiosis (Babesia microti Franca) are enzootic. Following blood-feeding, wasp-parasitized ticks are destroyed by the developing wasp. The prevalence of either human pathogen in host-seeking ticks collected in wasp-infested sites is nearly 40% lower than that found in other sites. Nymphal ticks, collected early in their season of activity, are more frequently parasitized by the wasp and less frequently by the Lyme disease spirochaete than those collected later in the summer. Spirochaetes never infected wasp-infected ticks, and few wasp-infected ticks were concurrently infected by the Babesia piroplasm. Taken together, these correlations indicate that the wasp may render the tick inhospitable to both pathogens. The presence of the wasp may have reduced risk of human infection on the island by either pathogen by as much as a third.

Theileria annulata was transmitted transtadially by an Israeli strain of Hyalomma excavatum from larvae to nymphs and from nymphs to adults. However, the adults developing from larvae which engorged on infected calves and fed during the nymphal stage on non-infected calves, rabbits or gerbils (Meriones tristrami), did not transmit theileriosis. Suspensions of infected unfed nymphs or adults did not produce theileriosis but both nymphs and adults of the same batch became infective to cattle after 2 days of feeding. Suspensions of salivary glands or of whole ticks derived from infected adults that remained attached to rabbits for more than 7 days, were not infective to cattle.

Transstadial transmission of Theileria annulata with Hyalomma anatolicum anatolicum, H. dromedarii and H. marginatum isaaci, and Haemaphysalis bispinosa, Rhipicephalus haemaphysaloides haemaphysaloides and Boophilus microplus was determined. It was found that the infection was successfully transmitted by H. a. anatolicum from larva to nymph and nymph to adult in all attempts. When larvae were fed on an infected calf the succeeding adults transmitted the infection when the intervening nymphs fed on a rabbit (non-susceptible host) but not when fed on a calf (susceptible host). Infective adult ticks transmitted the parasite during the first 24 h of feeding on a calf. When the feeding was interrupted after 24 h, and the tick transferred to another calf, the infection was transmitted to the latter as well. H. dromedarii successfully transmitted the infection from larva to nymph and from nymph to adult. Larvae of H. marginatum isaaci did not feed on calves but the infection was successfully transmitted from nymph to adult. Haemaphysalis bispinosa, Rhipicephalus h. haemaphysaloides and Boophilus microplus did not transmit Th. annulata from larva to nymph to adult.

Theileria mutans (Chisamba) was isolated from a steer at Chisamba, Central Province, Zambia by inoculation of blood into a susceptible unsplenectomised calf. The parasite was then transmitted on three occasions by nymphs and once by adult Amblyomma variegatum ticks. Macroschizonts, typical for T mutans, were detected in two calves for short periods. The parasite caused varying degrees of anaemia in all experimental calves, whose sera showed high antibody titres to T mutans in the indirect fluorescent antibody test.

Babesia motasi (Wales) was transmitted to sheep by larvae, nymphs and adult female Haemaphysalis punctata ticks which were either collected from rough grazing pasture, at Mynydd Mawr, Aberdaron, North Wales, or from laboratory cultures derived from ticks collected at the above site. Both transovarial and transstadial transmission of infection were demonstrated. Only larvae were shown to pick up infection. The parasite could not be demonstrated in intact sheep, either in blood films or following passage of whole blood from intact into splenectomised sheep. Organisms were detectable only in peripheral blood following blood transmission between splenectomised animals or in splenectomised sheep which were tick-infested. In such sheep a parasitaemia occurred 8-9 days after infected ticks started to feed and was accompanied by a mild fever. Splenectomised animals which recovered from acute infection remained as subclinical carriers but infection was eliminated with Ludobal, rendering animals resusceptible to infection. Morphological studies indicated that B. motasi (Wales) is similar to descriptions of isolates in Sweden, Holland and W. Germany but unlike an isolate from Turkey. The most common form is is a double pyriform with a mean length of 2.234 micron.