Factors affecting duration and intensity of trypanosome infection of domestic animals

Domestic animals can become infected with several species of trypanosomes that are transmitted by tsetse, including Trypanosoma congolense, T. vivax, T. brucei, T. simiae, T. rhodesiense and T. gambiense. The intensity and duration of the resulting parasitaemia are affected by the parasite, the host and detection methods. Techniques currently used to detect parasites range in sensitivity from one to 10(5) organisms per ml. At the same time, parasite kinetics vary greatly both within and between species of trypanosomes, although as a rule, at least for cattle, it is usual for T. vivax to give rise to higher parasitaemias (greater than 10(6) per ml) than T. congolense (less than 10(6) per ml) which is generally more persistent, while T. brucei results in only scanty transient parasitaemia (less than 10(5) per ml). It should also be appreciated that both T. vivax, and T. brucei, unlike T. congolense, invade tissues. Species of the host infected has a significant effect on parasitaemia patterns, e.g., in contrast to cattle, dogs develop high parasitaemias (greater than 10(7) per ml) when infected with T. brucei. Certain animals possess a remarkable inherent capacity to control, reduce and even self-cure infections, irrespective of the species of infecting trypanosome. This is best demonstrated by trypanotolerant breeds of cattle such as the NDama and West African Shorthorn, as well as by most species of wild Bovidae and Suidae. Physiological and environmental factors can probably influence the kinetics of infection but these are poorly defined and await quantification.(ABSTRACT TRUNCATED AT 250 WORDS)