Anaplasmosis – a little-known tick-borne zoonosis. The series ‘Veterinary Science and Practice in the 21st Century’

Anaplasma phagocytophilum is a bacterium transmitted by ticks of the genus Ixodes. It infects and resides in granulocytes, which is why the disease caused by it has been named granulocytic anaplasmosis. The disease is a potentially fatal multi-organ disease of humans and animals, characterised by low platelet counts in the blood picture. The first human deaths occurred in the United States as early as the 1980s. The first human cases were described in Poland at the beginning of the current century.

Ixodes ricinus ticks are the main vector of A. phagocytophilum in Europe, and most cases of anaplasmosis are reported in spring and autumn, during periods of tick activity. Ticks become infected when feeding on infected domestic and wild animals.

Symptoms of anaplasmosis include high fever, swollen limbs, petechiae, and animals are lethargic and weakened. Flu-like symptoms occur in humans, but the disease can be asymptomatic in both humans and animals. The severity of clinical signs of granulocytic anaplasmosis varies depending on the condition and age of the infected individual.

The diagnosis of anaplasmosis is based on history, clinical examination and laboratory findings. Microscopic examination of blood smears taken from diseased animals and humans can reveal the presence of characteristic structures called morulae. These structures are present in the cytoplasm of graulocytes before the administration of tetracyclines, and their number decreases rapidly after the administration of the antibiotic. When stained, morulae can be seen as dark blue to purple colour inclusions, made up of many delicate initial bodies.

Fig.1. Morula of A. phagocytophilum in a granulocyte.

The microscopic examination used to diagnose anaplasmosis is not a perfect diagnostic method. It requires considerable experience and does not always reveal the presence of morulae. Suspicion of the disease should then be confirmed by molecular and/or serological tests. In particular, rapid diagnostic tests based on immunochromatographic techniques have proven to be effective and easy to apply in the clinical setting.

Tetracyclines are the most effective group of antibiotics in the treatment of anaplasmosis. A significant improvement in the patients’ condition is observed within 12-48 hours of starting tetracycline therapy. Prevention of the disease consists of controlling ticks and not allowing them to feed on the body. There is no vaccine against granulocytic anaplasmosis on the market.

Human cases can occur as a result of blood transfusions containing the bacterium. Also, contact with the blood of wild animals can cause people to contract anaplasmosis. There are known cases of people wor king with wild game meat being infected. A case of perinatal transmission of A. phagocytophilum has also been described, however, cases of granulocytic anaplasmosis among humans are rare.

This tends to be the cause in lethargic animals with high fever that have been in contact with A. phagocytophilum ticks. The correct diagnosis of the disease is important for at least two reasons. Firstly, granulocytic anaplasmosis poses a threat to human health, so recognition of the animal disease and its continuous monitoring are factors that help reduce the danger of its human cases. On the other hand, rapid recognition of the disease allows early treatment and a complete cure.

Beata Dzięgiel-Michałowska, PhD, DVM
Department of Epizootiology and
Clinic of Infectious Diseases,
Veterinary Medicine Faculty,
University of Life Sciences in Lublin,
30 Głęboka Street, 20-612 Lublin

References and literature:

Adaszek Ł., Klimiuk P., Skrzypczak M., Górna M., Ziętek J., Winiarczyk S. 2012. The identification of Anaplasma spp. isolated from fallow deer (Dama dama) on a free-range farm in eastern Poland. Polish Journal of Veterinary Sciences, 15, 393-394.

Adaszek Ł., Górna M., Skrzypczak M., Buczek K., Balicki I., Winiarczyk S. 2013. Three clinical cases of Anaplasma phagocytophilum infection in cats in Poland. Journal of Feline Medicine and Surgery, 15, 333-337.

Bown K.J., Begon M., Bennett M., Woldehiwet Z., Ogden N.H. 2003. Seasonal dynamics of Anaplasma phagocytophila in a rodent-tick (Ixodes trianguliceps) system, United Kingdom. Emerging Infectious Diseases, 9, 63–70.

Lappin M.R., Breitschwerdt E.B., Jensen W.A., Dunnigan B., Rha J.Y., Williams C.R., Brewer M., Fall M. 2004. Molecular and serologic evidence of Anaplasma phagocytophilum infection in cats in North America. Journal of the American Veterinary Medical Association, 225, 893–896.