Tick-borne diseases of sheep and goats caused by Babesia, Theileria or Anaplasma spp.

A review is given on the Babesia, Theileria, and Anaplasma species infecting sheep and goats. B. ovis is the most important disease agent. It is transmitted by Rhipicephalus bursa, R. turanicus, Hyalomma anatolicum excavatum, and probably by R. evertsi evertsi B. ovis is widely spread in southern Europe, the Middle East, and central Asia. Its geographical distribution in South and East Asia and in Africa is widely unknown. B. motasi obviously represents several nosodemes in separate regions. It is not pathogenic for intact sheep in northern Europe, whereas it is probably more pathogenic than B. ovis in India and northern Africa. The known vectors of B. motasi are Haemaphysalis punctata and R. bursa. Theileria hirci is transmitted by H. a. anatolicum but occurs outside the distribution area of this tick. Malignant theileriosis of sheep and goats is an important disease in Iraq, Iran, and India. An attenuated macroschizont vaccine is successfully being used in Iran. Anaplasma ovis is transmitted by R. bursa and probably other ticks in the Old World and by Dermacentor andersoni in the New World. A. ovis is widely spread in the Old World. Outbreaks occur only under extreme conditions. The identity of the tick-borne disease agents of sheep and goats and of their vector ticks is uncertain in many regions of the Old and the New World.

Effect of management and inherent factors on birth seropositivity and seroconversion to Babesia bovis in calves in Costa Rica.

The relationship between calf characteristics, farm management, seropositivity, and age at seroconversion to Babesia bovis was assessed. A total of 3624 samples obtained from 494 animals on 11 farms was analyzed by an indirect ELISA assay, and individual results classified as positive or negative. The animals were sampled from birth to weaning, beginning in April 1990 and ending in April 1992. We found 59.1% (n = 467) of seropositive neonatal calves (mean age 4.4 days). Using a logistic binomial regression model as the analytical method for predicting the likelihood of calf seropositivity, we found that the following factors were related to seroconversion at birth: time to colostrum consumption, place of birth, calving history, parity (number of lactations), and ecological life zone. To analyze the effect of management factors on time to seroconversion, we used the Proportional Hazards method. In this model the pattern of seroconversion was different for the type of production system. Calves from dual-purpose farms seroconverted earlier than calves from cow-calf farms.

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.