16/11/2023
Tickborne fever is a febrile disease of domestic and free-living ruminants in the temperate region in south Africa, A similar disease transmitted by other ticks has been described in South Africa. The main hosts are sheep and cattle, but goats and deer are also susceptible.
After infestation with infected ticks, the incubation period may be 5–14 days, but after injection with infected blood, the incubation period is 2–6 days. In sheep, the main clinical sign is a sudden fever (105°–108°F [40.5°–42.0°C]) for 4–10 days. Other signs are either absent or mild, but the animals generally appear dull and may lose weight. Respiratory and pulse rates are usually increased, and a cough often develops.
Lesions:
Tickborne fever is characterized by transient but distinct hematologic changes. A modest neutrophilia develops 2–4 days after natural or experimental infection and is followed by a severe leukopenia due to lymphocytopenia and neutropenia. The lymphocytopenia lasts 4–6 days, whereas the neutropenia develops progressively and becomes more marked ~10 days after infection. Studies with monoclonal antibodies that recognize surface markers for lymphocyte subsets have shown that both T and B lymphocytes are reduced. The number of circulating eosinophils is also depressed for as long as 2 wk. After the febrile period has subsided, the number of monocytes may increase. At the peak of reaction, >90% of circulating neutrophils and eosinophils may be infected. The monocytes are predominantly infected during the later stages of bacteremia, whereas the granulocytes are usually infected throughout the period of bacteremia. The number of circulating thrombocytes is also reported to be depressed during the febrile period, and the occasional hemorrhagic syndromes associated with tickborne fever are probably related to the reduction in circulating thrombocytes.
Treatment & Control
The short-acting oxytetracyclines are regarded as the most effective treatment, because other antibiotics such as penicillin, streptomycin, and ampicillin do not prevent relapses. Sulfamethazine has also proved useful. If dairy cattle are treated with oxytetracyclines within a few days of infection, the pyrexia is reduced quickly and milk yield restored.
There are three important aspects of control: vector control, chemotherapy, and immunity. Effective control can be achieved by eliminating or markedly reducing contact with the tick vector either by grazing sheep and cattle on tick-free pastures in lowland areas or by use of acaricides. In sheep practice, this commonly involves keeping ewes and lambs in a fenced, relatively tick-free pasture until the lambs are ~6 wk old.
Yours In Service
MD Sentsho (Para Veterinarian)
