Summary.Bovine tropical theileriosis (Theileria annulata infection) is of great economic impor tance to several countries of Asia and Africa where millions of cattle are at risk of exposure to this disease. The authors describe symptoms, sequence of appearance of the parasite and pathology of the infection by three virulent strains of the parasite in fully susceptible calves.Symptoms observed were: enlargement of local lymph gland, fever, haemorrhages on visible mucous membranes and sometime on skin, anaemia and jaundice particularly in subacute and chronic forms of the disease.The parasite "schizont" was first detected in the swollen local lymph gland draining the site of attachment of ticks, then in other lymph glands which concurred with the onset of fever.Main post-mortem findings were: oedema and enlargement of, and haemorrhages in lymph glands and spleen, haemorrhages in subcutis and on most of the serous and mucous membranes, on endocardium, pericardium and epicardium, and ulcers in abo masum which rarely extended to intestine, oesophagus, tongue and gums. The microsco pic lesions were characterized by hyperplasia of lymphoid cells at the haemopoietic cen tres in lymph glands and spleen followed by regression and degeneration of the ger minal centres. Infiltration by lymphocytes and macrophages was observed in intermysial (heart) and periportal (liver) areas and in interstitial spaces in kidneys. T. annulata para sitises lymphoid cells. It provides stimulus for accelerated production of the cells which results in hyperplasia of the lymphoid tissue. Increased activity of the reticular tissue is a protective phenomenon.
Transstadial transmission of Theileria annulata with Hyalomma anatolicum anatolicum, H. dromedarii and H. marginatum isaaci, and Haemaphysalis bispinosa, Rhipicephalus haemaphysaloides haema-physaloides 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 (nonsusceptible 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.
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