Summary :Nine splenectomised calves were infested with dissimilar numbers of adult Boophilus microplus ticks 72 h after collection as engorged nymphs from three non splenectomised calves with different levels of Anaplasma marginale rickettsaemia. Successful transmission of A. marginale appeared to be more dependent on the level of rickettsaemia of the donor calves than on the number of ticks attaching to the splenectomised calves, since infection was transmitted only when the rickettsaemia was 0.3 % or greater. Field transmission would thus depend on the rate of tick migration amongst susceptible hosts and the rickettsaemia level of cattle on which the ticks fed previously.

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A survey of whipworms was conducted in llamas and vicuñas in northwestern Argentina. Fecal examinations of a group of 14 llamas (April 1995-March 1996) and 69 vicuñas (November 1996) indicated a high prevalence (usually >50%) of Trichuris sp. in these hosts. Prevalence was highest during July-November 1995 that also coincided with the highest mean fecal egg count. During postmortem examinations of 1 llama and 1 vicuña, specimens of Trichuris tenuis were recovered from the cecum/large intestine of each camelid. This is the first report of T. tenuis in South America, and the first report in the vicuña. It is suggested that T. tenuis is the typical whipworm of aboriginal camelids.

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