The effect of the ovine host parasitaemia on the development of Babesia ovis (Babes, 1892) in the tick Rhipicephalus bursa (Canestrini and Fanzago, 1877)

Batches of Rhipicephalus bursa adult ticks were fed on two lambs with 10.0% (batch 1) and 0.3% (batch 2) Babesia ovis parasitaemia, respectively. Haemolymph and eggs were checked for parasites daily after detachment, before and after appearance of B. ovis in the lamb's blood.B. ovis kinetes were found in the haemolymph and eggs earlier in the engorged ticks detached before appearance of the parasite in the host blood. Rates of haemolymph and egg infection with B. ovis as well as the percentage of infected eggs were much higher in batch 1 (10% lamb parasitaemia) than in batch 2 ticks (0.3% lamb parasitaemia). In eggs incubated at 28 degrees C the optimal period to look for kinetes seems to be days 4-9. Heavily infected ticks laid fewer less eggs within a shorter oviposition period. Pre-oviposition, pre-hatching periods and egg hatchability were not affected. Various parasitic forms are described in the haemolymph and the eggs.     

Notes on the biology of the tick Rhipicephalus bursa (Canestrini and Fanzago, 1877) in Israel

The seasonal distribution of the tick Rhipicephalus bursa in sheep has been studied during one year in two neighbouring flocks of Awassi sheep in an enzootic focus of sheep babesiosis. Rates of tick infestation on the two flocks were very different. Pre-imaginal stages were found on the sheep during the winter months of November-March while adult ticks appeared in the middle of April and persisted until the end of July. First clinical cases of babesiosis in sheep were diagnosed 2 weeks after finding the first adult ticks. The pre-imaginal stages were found mainly in the pinnas while adult ticks preferred in decreasing order the tail, body and head. Few adult ticks were found on the legs.     

The life cycle of Rhipicephalus bursa Canestrini and Fanzago, 1877 (Acarina: ixodidae) under laboratory conditions

The biology of Rhipicephalus bursa has not been thoroughly studied. In the present study R. bursa was bred in the laboratory and its biology worked out.Larvae, nymphs and adult Rhipicephalus bursa ticks were fed on sheep and were held at 28+/-1 degrees C and 89+/-1% relative humidity (RH) in a darkened incubator. The average weight of engorged females was 0.676g (range 0.353-1.128). The average weight of eggs laid by females was 0.344g (range 0.146-0. 554g). The average number of eggs laid was 7527 (range 6263-8860) and this was significantly correlated with the weight of the females. The index of Reproduction Efficiency (number of eggs per g weight of female) was 8469.6. The index of Conversion Efficiency (weight of eggs per weight of female) was 0.5037.Peak daily oviposition, at an average of 840 eggs per female, occurred on the 6th day of oviposition. After Day 6, the rate declined steadily. The average duration of the preoviposition period was 5.1 days (range 4-7 days). The oviposition period averaged 16.5 days (range 12-21 days), and was significantly related to both the weight of the female and the number of eggs laid. The average pre-hatching period was 31.2 days (range 24-45 days). The average feeding time of larvae and nymphs of this two host tick was 15.2 days (range 14-18 days). Female ticks fed for 5.9 days on the average.Heavier nymphs produced females and a shorter premoult period was noted for lighter male nymphs. The males/females ratio was 1.38:1. The time taken to complete the life cycle was on average 142.45 days (range 99-254 days).     

Attenutation of Babesia ovis by rapid successive passages in splenectomized lambs

Sheep babesiosis, caused by Babesia ovis (Babes, 1892) is one of the most important sheep diseases in the Mediterranean zone, as well as in other infected areas infested by the vector tick Rhipicephalus bursa (Yeruham et al., 1992, 1995). Attenuated strains of Babesia bovis following rapid blood passages in splenectomized calves have been used as a vaccine (Callow and Mellors, 1966; Stewart, 1978). In the work reported here, rapid passages of B. ovis parasites in splenectomized lambs, using blood collected at the acute stage of the disease, were carried out and their effect on the virulence of the parasite was examined.     

A study of an enzootic focus of sheep babesiosis (Babesia ovis, Babes, 1892)

Morbidity and mortality due to Babesia ovis in sheep flocks grazing in an enzootic area of Israel occur yearly, about 2 weeks after detection of adult Rhipicephalus bursa ticks on the animals. Disease incidence peaks in May, but lasts throughout the active period of the adult ticks in the spring-summer months of April–July. No clinical cases of babesiosis have been registered during the active period of the preimaginal stages of R. bursa, from October to February. Incidence of parasitaemia during the spring-summer months was variable, ranging between 2 and 25%. However, in the winter months the incidence of parasitaemia in hoggets increased considerably, reaching 4–60% of the animals.

A positive serological response to B. ovis was found in 84.5% of the hoggets and 88.9% of the ewes. In ewes, the prevalence of the serological response showed no marked seasonal variations. Colostral sera of 67.5% and 75% of the ewes and hoggets, respectively, were serologically positive for B. ovis. No antibodies were detected in the sera of lambs less than 3–4 months of age. The epizootiology of sheep babesiosis appears to differ from that of bovine babesiosis.