Dermacentor variabilis were infected as nymphs with Anaplasma marginale by allowing the ticks to feed on a single infected donor calf. Two weeks after molting to the adult stage, the ticks were allotted into 1 of 3 groups and were allowed to overwinter at room temperature (25 C) in the laboratory (group 1), cold storage (4.5 C) in the laboratory (group 2), or outdoors in leaf litter (group 3). Persistence of A marginale was assessed by determining density of colonies (number of colonies/0.1 mm2 of gut tissue examined) in tick gut specimens at 3, 5, 7, 9, and 12 months after molting to the adult stage. Colonies of A marginale were found in all groups at every density evaluation period. Highest colony densities were observed uniformly in specimens collected at month 7 (May); densities decreased at month 9 and were lowest at month 12. Statistical analysis indicated that ticks subjected to cold storage and to outdoor conditions had similar colony densities of A marginale; the density curve in these 2 groups indicated significant quadratic effects over time, with peak densities in May. Mean colony density in ticks kept at room temperature fit a different quadratic equation. The morphologic data indicated that A marginale overwinters in Dermacentor variabilis, and that increasing numbers of organisms are found from January to May.
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Article Synopsis
- Anaplasma bovis is a disease-causing agent primarily affecting ruminants and has been mostly found in Asia, the Middle East, and Africa; rare human infections have been reported, mainly due to Anaplasma phagocytophilum.
- A study aimed to check the prevalence of an A. bovis-like agent in the Southcentral U.S. found it in 3.1% of ticks from Oklahoma, but no presence was detected in cattle blood.
- The results suggest that the A. bovis-like agent is likely present in the U.S. and could be a potential zoonotic threat, highlighting the need for further research to identify its reservoirs and assess the human infection
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