Factors influencing the transmission and incidence of tropical theileriosis (Theileria annulata infection of cattle) in Morocco.

A longitudinal epidemiological investigation of tropical theileriosis was carried out in an endemic region of Morocco during the 1991 disease season. This involved approximately 220 cross-bred cattle on 15 farms. Data were collected on the frequency of existing infections, the size of the vector tick population and the incidences of new infections and clinical disease, and these were then analysed using statistical models. The prevalence of subclinically infected carriers of Theileria annulata, the number of adult Hyalomma detritum, the vector, and the probability of becoming newly infected with T. annulata increased significantly with the age of cattle, although the age effect on new infections may be a result of increased tick numbers on older animals. The probability of clinical disease in newly infected cattle was not significantly influenced by age or by the number of adult ticks, but was significantly positively associated with the cattle population on the farm. The number of H. detritum nymphs counted on cattle in the autumn was related significantly to the previous adult tick count on the same animal.

Prevalence of Theileria in the tick Hyalomma detritum detritum in the Doukkala region, Morocco.

The overall prevalence of Theileria species, mainly, if not exclusively, T.annulata, in 901 Hyalomma detritum detritum collected from cattle in the Doukkala region of Morocco over a period of 2 years was 21.5%. The quantity of infection (number of sporoblasts per infected tick) followed the negative binomial distribution with between one and 250 sporoblasts per infected tick. Infected ticks were found in eight of fourteen areas examined whilst T.annulata was present in all fourteen. There were significant differences in both the prevalence and the quantity of infection between ticks collected from different farms, and between nymphs collected in the autumn from these farms, and moulted in the laboratory, and adults collected in the following summer. The prevalence, but not the quantity, of infection was higher in female than in male ticks. No correlations were established between infection of engorged nymphs and the breed, sex and Theileria piroplasm parasitaemia of the host animal. However, calves infected a greater proportion of nymphs than adult cattle and the heavier the infestation of nymphs on an animal, up to a plateau, the higher the prevalence of infection in those nymphs. There were no differences in infection between ticks moulted at 24 degrees C and 37 degrees C, after the engorged nymphs had been stored at 18 degrees C to simulate over-wintering.

Common and stage-specific antigens of Theileria annulata.

Western blot analysis of Theileria annulata antigens was carried out using sera collected from cattle which had been immunised and challenged with either T. annulata sporozoites or schizont-infected cells. Three antigens between 71 and 73 kDa proved to be common to the three stages of parasite studied: sporozoites, schizonts and piroplasms. An antigen was found at 32 kDa which was specific to T. annulata piroplasms. Results were reproducible using sera from Morocco and the UK. At least one of the proteins at 71-73 kDa, but not that at 32 kDa were also recognised by sera from animals infected with Babesia species.

The epidemiology of tropical theileriosis (Theileria annulata infection in cattle) in an endemic area of Morocco.

A longitudinal study of tropical theileriosis was performed on 12 farms in the Doukkala region of Morocco during 1990. Adult Hyalomma detritum detritum were collected between March and early October and a peak in numbers was observed at the end of June. Nineteen percent (24/127) were infected with Theileria species and, amongst these, over 50% had five or more sporoblasts in their salivary glands (range 1-151). Hyalomma d detritum larvae and nymphs were found on cattle between September and early December with the highest numbers in late October. The prevalence of T. annulata piroplasm carriers at the beginning of the year was 48.5% (47 positive out of 97) and there were 14 new infections during the disease season (March to September) of which five developed into clinical cases. The incidence rates of new infection and clinical disease were 0.156 and 0.056 per animal-season, respectively. Differences were observed between age categories of cattle in both tick and parasite infections. A significantly lower number of adult H.d. detritum were collected from calves than from adult cattle. The prevalences of piroplasm carriers before the disease season were 0%, 36% and 76%, respectively, in (a) calves which had been born since the previous disease season, (b) calves born before then and (c) adults. However, the incidence rates of infection and disease for uninfected animals in the two categories of calves were approximately the same: 0.299 and 0.378 new infections, and 0.085 and 0.126 clinical cases per animal-season for (a) and (b), respectively. The date predicted for the appearance of adult H.d. detritum, based on published tick development times and local temperature records, was within 2 weeks of the study visit when the highest number of adults were collected from cattle. However, the date predicted for the appearance of larvae was 6 weeks earlier than the observed peak populations and may indicate that H.d. detritum delays either egg laying in the summer or larval host searching in the autumn.

Epidemiological observations on Gasterophilus intestinalis and G. nasalis in donkeys from Morocco.

During a 24 month period, 198 donkeys were examined for Gasterophilus intestinalis and Gasterophilus nasalis larvae. Gasterophilus intestinalis was found in 97.5% and G. nasalis in 95.5% of donkeys. The third instars (L3) of both species occurred during all months of the year and so did the second instars (L2), except in April (G. nasalis) and May (G. intestinalis). Over 75% of the animals had up to 200 larvae and 1.5% had over 600 larvae. The maximum number of both L2 and L3 larvae found in any animal was 418 G. intestinalis, 433 G. nasalis and 715 of both species combined. The seasonal variation in the numbers and development status of larvae indicated that the period of greatest activity of adult flies of G. intestinalis was from August/September to November, and that of G. nasalis from May to September. Consequently, the L2 larvae in the stomachs were in peak numbers between November and January for G. intestinalis and between July and September for G. nasalis. The L3 larvae of G. intestinalis had peak numbers between December and July, and those of G. nasalis between October and March. During January-March, most of the L2 larvae of G. nasalis were trapped in polypous nodules near the pyloric end of the stomach. It is concluded that the high-risk period for infection is during late spring and autumn, leading to the heavy larval burden of Gasterophilus in the stomach of donkeys during winter.

Epidemiological observations on stomach worms of donkeys in Morocco.

Over two consecutive years, weekly examinations for the presence of nematodes were conducted on 185 stomachs from donkeys originating mainly from the Rabat, Casablanca and Settat regions of Morocco. All the animals, except one, were infected by at least one of four helminth species. Trichostrongylus axei was found in 93.5%, Habronema muscae in 89.7%, H. majus in 85.4% and Draschia megastoma in 1.1% of donkeys. Most animals were infected by two (23.8%) or three (71.9%) species. High burdens of T. axei were observed in the winter of both years and in the mid-summer of the second year. Peak burdens of Habronema were found at various times throughout both years. There were more adult H. majus than H. muscae. The periods of peak levels of infection by these parasites were related to environmental conditions suitable for the development and survival of infective larvae of T. axei and for the build-up of muscid fly vectors of Habronema and Draschia spp.

Epidemiology of gastrointestinal helminths of sheep in the Rabat area of Morocco.

The epidemiology of gastrointestinal helminths of sheep on permanent pastures in Morocco was studied by monthly examination of faeces of ewes for helminth eggs and by use of batches of 3 tracer lambs each month from December 1979 to November 1980. The main helminth genera encountered were Teladorsagia, Haemonchus, Trichostrongylus and Moniezia, with Nematodirus, Cooperia, Oesophagostomum and Trichuris occasionally recorded. The faecal egg counts of ewes showed 2 peaks; the first in March due to the acquisition of larvae during the rainy season and periparturient rise, the second in October probably due to maturation of inhibited larvae. The worm burdens of tracer lambs showed that there was a gradual accumulation of nematodes from December, reaching a peak in May; an absence of infection in July and August during the dry period, and a second peak in November. Infection by Moniezia was higher during the dry season.

The effect of dose and line on immunisation of cattle with lymphoblastoid cells infected with Theileria annulata.

Thirty-one Friesian calves in Morocco susceptible to tropical theileriosis were protected against a lethal sporozoite challenge by prior infection with lymphoblastoid cell lines infected and transformed in vitro by a Moroccan stock of Theileria annulata. The challenge infection of cryopreserved sporozoites killed all four susceptible control calves within 20 days. Four schizont-infected cell cultures at Passage 3 were inoculated at four different doses, 10(8), 10(6), 10(4) and 10(2), into pairs of calves. The recipient animals showed great variation in severity of disease symptoms, which did not show a linear correlation with the cell dose inoculated. The most severe disease symptoms were recorded, prior to challenge, in the 10(2) cell dose recipients; one animal died of acute theileriosis and another had to be treated. One of the four cell lines used was more virulent than the other three. Two years after the completion of this experiment, immunised animals have shown normal productivity traits.

The effect of MHC compatibility between parasite-infected cell line and recipient in immunization against tropical theileriosis.

Lymphoblastoid cell lines, infected and transformed in vitro by a Moroccan stock of Theileria annulata, infected and immunized susceptible taurine cattle, at cell doses of 10(8), 10(6), 10(4) and 10(2), regardless of whether the recipients were BoLA matched or mismatched to the donor cell line. The MHC relationship between the cell line and recipient did affect the severity of the clinical response to cell line immunization which may reflect differences in the specific priming of the immune response. At the highest cell doses the BoLA-mismatched recipients reacted more severely than the BoLA-matched. This study shows that, unlike the closely related parasite T. parva, there is no histocompatibility barrier to immunization using T. annulata-infected cell lines which could be achieved with as few as 10(2) allogeneic infected cells. The role of MHC compatibility between cell line and recipient in the priming of a protective immune response is discussed.

Epidemiology of hydatidosis/echinococcosis in Ouarzazate, the pre-Saharian region of Morocco.

In the Ouarzazate province of Southern Morocco, 1085 cattle and 358 sheep were examined for hydatid cysts. The prevalence was 44.6% (range 8.3-83.4%) in cattle and 5.3% (range 1.3-28.6%) in sheep. The prevalence increased with the age of the animals. The lung was the predominant site of infection, followed by the liver. In cattle, 14.2% of hydatid cysts were fertile and 16.4% had degenerative changes. The mean loss per head of cattle slaughtered was about 1 kg of liver and 900 g of lungs in the urban abattoirs. In monetary terms at the current price of 1980, this meant a loss of U.S. +4.5 at urban and +1.6 at rural abattoirs. The mean prevalence of infection in 61 stray dogs was 50.8%, with a mean worm burden of 413. The urban dogs had a lower infection rate (42.9%) than the rural dogs (61.5%). There were 130 dogs per 1000 inhabitants. The human population was ignorant of the life-cycle of Echinococcus granulosus and was not aware of risk of infection through dogs. Dogs become infected at abattoirs, at home slaughter and in the field by consuming dead carcasses. The maintenance and transmission of E. granulosus in animals and man is related to social, religious and cultural factors.

Effect of temperature on transovarial transmission of Babesia bigemina (Smith and Kilborne, 1893) in Boophilus annulatus (Say, 1821).

The effect of the temperature on the transovarial passage of Babesia bigemina has been studied in female Boophilus annulatus during their oviposition. Kinetes of Babesia were present in eggs laid at the temperatures of 16, 20, 26, 28, 30 and 35 degrees C. The rate of infection was temperature dependent. It reached at least 50%, even at low temperatures. The average infection level at 26 and 30 degrees C was 270 kinetes per egg. However, between 20 and 35 degrees C the eggs laid during the first 3 days were parasite free. At 16 degrees C, no kinetes were detected during the first 13 days of oviposition.

The role of antibodies in immunity against Theileria annulata infection in cattle.

The role of antibodies in protecting cattle against Theileria annulata infection was investigated. It was found that serum samples from immune cattle had a neutralizing effect on the sporozoites preventing in this way the invasion of lymphocytes. However, the same antiserum neither caused lysis of macroschizont- infected lymphoblastoid cells nor inhibited their proliferation in vitro. Free merozoites but not the infected erythrocytes were opsonized by immune serum. In addition, complement alone, without antibody participation, was able to lyse free merozoites. The importance of humoral factors in immunity to T. annulata infection is discussed.

Effect of infection by Babesia spp. on the development and survival of free-living stages of Boophilus annulatus.

Oviposition, egg hatching and survival of newly-hatched larvae of Boophilus annulatus were studied in relation to infection by Babesia species and different temperature regimens. Infection of female ticks by Babesia bigemina or B. bovis had no effect on the time elapsed between engorgement and oviposition. The duration of oviposition was shorter in infected females incubated at 25 degrees C or 35 degrees C and infected females laid fewer eggs than the controls. No larvae hatched at 16 degrees C. B. bigemina-infected eggs hatched more quickly than uninfected eggs at 35 degrees C. The hatching percentage of B. bigemina-infected eggs was reduced by 50% at an incubation temperature of 25 degrees C and by 75% at 35 degrees C. At 16 degrees C there was no difference in the duration of survival of infected and non-infected larvae but at 25 degrees C and 35 degrees C the mean survival period of infected larvae was significantly lower than those of controls.

Hydatidosis in sheep, goats and dromedaries in Morocco.

Two thousand two hundred and forty-six sheep, 510 goats and 35 dromedaries were examined for hydatid cysts. The mean prevalence was 0.7% (range 0.4-38.5%) in sheep, 1.4% (range 0.2-7.7%) in goats and 80% in dromedaries. The increase in prevalence with age of the animals was statistically significant in sheep only. In all species examined infection of the lungs was more common and important than that of the livers. The fertility rate of hydatids was 50% in sheep and 67.8% in dromedaries; and degenerative changes were shown by 65.8% of hydatids from dromedaries as compared to 16.3% in sheep. Dromedaries seem to play an important role in the epidemiology of hydatidosis in Morocco.

Epidemiology of Oestrus ovis infection of sheep in Morocco.

The epidemiology of Oestrus ovis was studied by two methods, slaughterhouse survey and tracer lambs study. The prevalence of infection varied from 10 to 100%, the highest being between June and September and the lowest in March. The mean annual larval burden was 6.7. The maximum number of larvae recovered from a single head was 35 in the month of September. Two larval peaks were observed, the first in May and June and the second in September and October. The flies are absent from December to March. The first generation flies appear in April and up to four generations may occur during the year. During the hottest month of the year (August) flies are either absent or in negligible numbers. During winter the perpetuation of species is ensured by the overwintering larvae in the heads of sheep and the pupae on the ground.

Development of Hyalomma lusitanicum under laboratory conditions.

At the constant temperature of 25 degrees C and relative humidity (RH) of 84%, the average pre-oviposition period of Hyalomma lusitanicum was 47 days, the oviposition lasted an average of 26 days and the total egg production was an average of 6320 per female. At 16 degrees C the females did not lay eggs at all, but those which survived for 1 year and were transferred thereafter to 25 degrees C and 84% RH laid viable eggs. At 35 degrees C, the oviposition was identical at all levels of RH tested (25, 62 and 93%). At 25 degrees C, the pre-oviposition period was shorter at 93% RH, and the number of eggs laid was fewer at 25% RH. The eggs hatched in 32-40 days, the hatching percentage being lower in batches of eggs laid at the beginning and at the end of the oviposition period. The larval and nymphal moultings were not influenced by the type of host. As the temperature increased, the pre-moult period became shorter. The engorged larvae were more sensitive to the low RH than the engorged nymphs, whose moulting percentage was always greater than 72 in all regimes. Low temperature and high humidity had a favourable effect on the survival of unfed nymphs. The female-to-male ratio was 1:2. Hyalomma lusitanicum always behaved as a 3-host tick. The adults did not engorge on rabbits. The female ticks engorged on calves weighed an average 543 mg. Ticks maintained at 25 degrees C and 84% RH and engorged on calves completed the life cycle in 138-196 days, which does not include the period of chitinization of about 30 days. More than half of this period was spent in egg laying and hatching.