Tick abundance and seroconversion rates of 640 indigenous cattle in a mixed crop-livestock system in Uganda were investigated in a 14 months longitudinal study. Up to 100% of the cattle in Buyimini, Kubo, Nanjeho, Ojilai and Sitengo villages (high tick challenge zone) were consistently infested with Rhipicephalus appendiculatus, whereas on average 50% of the cattle in Bunghaji, Hitunga and Magoje villages (low tick challenge zone) were inconsistently infested. Likewise, up to 50% of the cattle in Buyimini, Kubo, Nanjeho, Ojilai and Sitengo villages were consistently infested with R. (Boophilus) decoloratus ticks, while on average 30% of the cattle in Bunghaji, Hitunga and Magoje were inconsistently infested. Seroconversion rates of cattle to Anaplasma marginale infection under low tick challenge were higher than those under high tick challenge, but the reverse was true for Babesia bigemina infection. For Theileria parva infection, seroconversion rates of cattle older than 6 months under low tick challenge were significantly higher than those under high tick challenge (P < 0.05). However, the likelihood of occurrence of theileriosis cases among calves (0-6 m) under high tick challenge was 6 times (Odds ratio = 5.82 [1.30-36.37]) higher than under low tick challenge. The high density of anti-tick plants Lantana camara and Ocimum suave that were widespread in villages with low tick challenge, among other factors, was probably the cause for unfavourable tick survival.

A cross-sectional study was conducted in Uganda between November 2006 and February 2007 to assess the seroprevalence and risk of brucellosis in zerograzing and pastoral dairy systems; two major sources of milk in Uganda, 80% of which is sold unpasteurized to consumers through informal channels. A total of 723 cattle comprised of 497 animals from the pastoral system and 226 animals from the zerograzing system were tested for antibodies against natural B. abortus infection using the competitive enzyme-linked immunosorbent assay (C-ELISA). Herd-level seroprevalence was 100% in the pastoral system and 5.5% (95% CI: 1.8, 9.2) in the zerograzing system. The animal-level seroprevalence and within-herd range of brucellosis in cattle in the pastoral system were 34.0% (95% CI: 29.9, 38.1) and 8.1-75.9%, while for those in the zerograzing system were 3.3% (95% CI: 0.9, 5.7) and 0-9.0%. Abortion rates of 23% and 0% among seropositive cows vis-à-vis 5.4% and 1.9% among seronegative cows were recorded in the pastoral and zerograzing systems, respectively. The risk of natural B. abortus infection was higher among older cattle (>24 m) (Odds ratio [OR] = 1.83, 95% CI: 1.25-2.67) and dry cows (OR = 2.01, 95% CI: 1.23-3.31) in the pastoral system, and in calves aged 0-6 m (OR = 5.72, 95% CI: 1.04-31.41) in the zerograzing system. Implementing a culling program in the zerograzing system to eliminate the existing low risk of brucellosis and targeting calves in the pastoral systems for vaccination could avert the cost-related limitation of brucellosis control in Uganda.

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