Trypanosoma congolense: lack of correlation between the resistance of cattle subjected to experimental cyclic infection or to field challenge.

Twelve male cattle of the Baoulé breed were exposed to natural trypanosome challenge in an area of high Glossina density, to characterize them as trypanoresistant or trypanosensitive. Weekly blood samples were taken for the determination of parasitemia and packed cell volume, as a measure of anemia. Seven Zebu cattle were also exposed to challenge at the same time. The Zebu proved to be trypanosensitive with high parasitemia, pronounced anemia and died or were drug treated in extremis. Five Baoulé were as sensitive as the Zebu while 7 others were trypanoresistant since they showed little or no patent parasitemia, only mild transient anemia and survived in good condition. The 12 Baoulé were allowed to recover from challenge in the field and along with 7 Zebu were subjected to experimental fly challenge in fly-proof accommodation. Glossina morsitans submorsitans infected with a clone of Trypanosoma congolense derived from the stock Serengeti/71/STIB/212 were allowed to engorge on the shaven flanks of tranquilized animals. All animals showed persistent parasitemia for at least 7 weeks, including all the Baoulé resistant to natural challenge. Two Baoulé, one resistant and one sensitive to natural challenge, and 4/7 Zebu appeared unable to control parasitemia, had severe anemia, and were drug treated in extremis. The remaining Baoulé, 6 resistant and 4 sensitive, appeared to be undergoing spontaneous cure by Week 9-10, as did 3/7 Zebu. In Zebu, anemia was as pronounced as under natural challenge. Three resistant Baoulé maintained packed cell volume above 30 as under field challenge but the others showed marked anemia. On the contrary, 4 sensitive Baoulé showed only slight anemia after artificial fly challenge.(ABSTRACT TRUNCATED AT 250 WORDS)