As ticks infected with T

As ticks infected with T. parva feed they inject sporozoites into the host. These parasites, localize and multiply in the lymph node that drains the site of the bite. The incubation period is 8–12 days with schizonts spreading to other lymph nodes. Clinical signs of East Coast fever and tropical theileriosis are similar and include high fever sometimes up to 42 °C because of the formation on numerous schizonts inside the lymphocytes which rapture,
accompanied by heavy swellings of the lymph nodes and the spleen. During this phase high death rates may occur before merozoites can be diagnosed in Giemsa stained blood smear preparations (Mizikar 2018). The other symptoms are depression, drooling, lacrimation, diarrhoea, anorexia, and weight loss, as well as decreased milk production. Petechiae and ecchymoses occur in the conjunctiva and oral mucous membranes. Corneal opacity is commonly observed. Severe pulmonary oedema with dyspnoea and a frothy nasal discharge is common and terminal in many animals, whereas others become prostrate and comatose. In T. parva infections erythrocytic schizogony is rare or absent but in the life cycle of
T. annulata it is present. Tropical theileriosis since the parasites rapture the red blood cells y icterus, anaemia, and occasionally hemoglobinuria are observed. Some animals with East Coast fever may develop a fatal condition called “turning sickness,” which is characterized by neurologic signs as a result of capillary impairment by parasites in the CNS. Sporozoites, of tick origin, invade and infect host lymphocytes and macrophages. Cell entry occurs through receptormediated parasite-directed phagocytosis. Infected lymphocytes are transformed in vitro into lymphoblastic cells. Macroschizonts
develop in the cytoplasm of the transformed cells and then divide synchronously with the host lymphocytes to infect their daughter cells
Extensive leukopenia is a sign of severe disease where the white blood cells can
disappear completely. Other clinical signs are anorexia, diarrhea, and soft coughs
due to accumulated ?uid in the lungs and thereby diffculties in breathing. Before
death of the animal, the temperature usually falls, and a frothy nasal discharge will
be visible due to the pulmonary edema (Fig. 8.5). Sometimes the parasite can
invade the central nervous system which can result in nervous signs—turning sickness—and paralysis. The degree of pyrexia and pathogen load usually determines the severity of the disease. Young cattle appear to be more resistant than older
animals, and Friesian-European breeds such as Friesian/Holstein appear to be
more susceptible to the disease than indigenous cattle. Mortality can reach close to
100% on herd level if no interventions are implemented. In addition to the breed
and age, the mortality also depends on the strain of the parasite and the amount of
parasite exposure. ECF is a sporozoite dose-dependent disease (Irvin and
Mwamachi 1983; OIE 2008).