308 



THE PIRCPIASMASIDA 



phagocytized by the salivary gland cells, 

 and the "sporoblasts" to be masses of 

 coalesced droplets secreted by the sali- 

 vary gland cells. Gonder's work has been 

 discredited not only by Reichenow but also 

 by Cowdry and Ham, Wenyon (1926) and 

 others. According to Cowdry and Ham, 

 Gonder did not distinguish between Theileria 

 and the symbionts which are present in all 

 ticks, and substantiating details in his ac- 

 count were conspicuous by their absence. 

 Wenyon said that his "account was so ob- 

 scured by such theoretical bias that it is 

 difficult to separate fact from theory. " 



A definitive study is badly needed to 

 clear up the life cycle of T. parra, and 

 one may hope that 20 more years do not 

 pass before someone carries it out. In the 

 meantime, Reichenow' s account is the most 

 convincing. 



Pathogenesis : T. parva is highly 

 pathogenic. From 90 to 100% of affected 

 cattle die, altho the mortality is lower in 

 endemic areas. In East Africa, for in- 

 stance, immature cattle are more resistant 

 than adults, and the mortality among calves 

 varies from 5 to 50%. In Kenya, the mor- 

 tality varies considerably among calves, 

 but adults usually die. 



The incubation period following tick 

 transmission is 8 to 25 days, with a mean 

 of 13 days. The disease itself lasts 10 to 

 23 days, with a mean of 15 days. Acute, 

 subacute, mild and inapparent forms of the 

 disease have been described, of which the 

 acute type is the usual one. 



In the acute form, the first sign is 

 fever. The body temperature varies from 

 104 to 107° F; it may continue high or it 

 may decrease after 7 to 11 days and then 

 increase again. Other clinical signs 

 usually appear a few days after the initial 

 rise in temperature. The animals cease 

 to ruminate and to eat. Other signs are a 

 serous nasal discharge, lachrymation, 

 swelling of the superficial lymph nodes, 

 sometimes swelling of the eyelids, ears 

 and jowl region, rapid heart beat, general 

 weakness, decreased milk production, 

 diarrhea, frequently with blood and mucus 

 in the feces, emaciation, coughing, and 

 sometimes icterus. Breathing becomes 

 rapid and dyspnea is pronounced just before 

 death. An oligocythemic anemia is pres- 



ent, but there is no hematuria in uncom- 

 plicated cases. 



In the subacute form, which is often 

 encountered in calves and sometimes in 

 adults in the endemic areas of East Africa, 

 the signs resemble those in the acute form 

 but are not so pronounced. Affected ani- 

 mals may recover, but it takes them sev- 

 eral weeks to return to normal. 



In the mild form, little is seen but a 

 relatively mild fever lasting 3 to 7 days, 

 listlessness and swelling of the superficial 

 lymph nodes. An inapparent form of the 

 disease has been produced by injection of 

 blood, coarsely ground spleen and lymph 

 node emulsions or suspensions from par- 

 tially engorged, infected ticks. 



The lymph nodes are usually marked 

 swollen, with a variable degree of hyper- 

 emia. The spleen is usually enlarged, 

 with soft pulp and prominent Malpighian 

 corpuscles. The liver is enlarged, fri- 

 able, brownish yellow to lemon yellow, 

 with parenchymatous degeneration. The 

 kidneys are either congested or pale 

 brown, with a variable number of hemor- 

 rhagic "infarcts" or greyish white lymph- 

 omatomata. The meninges may be 

 slightly congested. The heart is flabby, 

 with petechiae on the epicardium and endo- 

 cardium. The lungs are often congested 

 and edematous. There may be hydro- 

 thorax and hydropericardium, and the 

 kidney capsule may contain a large amount 

 of serous fluid. There may be petechiae 

 in the visceral and parietal pleura, adrenal 

 cortex, urinary bladder, and mediastinum. 

 There are characteristic ulcers 2 to 5 mm 

 or more in diameter in the abomasum, 

 and similar ulcers together with red 

 streaks or patches may be present thruout 

 the small and large intestines. These 

 ulcers consist of a central, red or brown 

 necrotic area surrounded by a hemorrhagic 

 zone. The Peyer's patches are swollen, 

 and the intestinal contents are yellowish. 



Immunity: Animals which recover 

 from T. parva infections are solidly im- 

 mune. The parasites disappear com- 

 pletely, and there is no premunition. 

 There is no cross-immunity between T. 

 parva and Goiidcria »uitaiis. but there is 

 partial cross-immunity between T. parva 

 and G. lawrencei. 



