General information
Based on genetic analyses, the former species Ehrlichia phagocytophila, Ehrlichia equi and the causative agent of human granulocytic ehrlichiosis (HGE) were unified in the new species Anaplasma phagocytophilum. In addition, infection with Anaplasma platys, the causative agent of infectious canine cyclic thrombocytopenia, plays an increasingly important role in Europe, too.
Anaplasma phagocytophilum
Anaplasma phagocytophilum is a gram-negative, obligate intracellular bacterium, which particularly infects neutrophil granulocytes and forms, when multiplying within the granulocytes, typical inclusion bodies, so-called morulae. In Europe, the main vector is Ixodes ricinus. Deer, mice and other rodents are reservoir hosts.
The clinical signs are similar to those of ehrlichiosis, but here, more thrombocytopenia can be observed more often, mainly because of the formation of anti-thrombocyte antibodies. Anaplasma infections can by asymptomatic, can cause non-specific symptoms (fever, inappetence, apathy) or severe symptoms (CNS disorders). In dogs, orthopaedic problems (myositis, joint swellings, lameness) are often associated with Anaplasma infections.
In horses, fever, apathy, limb oedema and reluctance to move are initially dominant. Horses older than 4 years show more obvious signs than younger animals. Once the infection is overcome, a resilient immunity is acquired for about 2 years.
In ruminants, Anaplasma phagocytophilum can cause tick-bite fever. Most infections progress subclinically, but fever and productivity loss or abortions are also possible. Severe cases occur when non-immune animals are introduced into endemically contaminated areas.
Anaplasma platys
Anaplasma platys (formerly Ehrlichia platys) is an obligate intracellular, gram-negative bacterium in dogs which multiplies in patelets and leads to cyclic thrombocytopenia and bacteraemia with intervals of approximately 14 days. The disease is called infectious canine cyclic thrombocytopenia. Descriptions of this species of Anaplasma come from overseas, but the pathogen is also detectable in the Southern Mediterranean (North Africa, southern Portugal, Andalusia, Sicily, southern Italy, southern Greece). It is transmitted through ticks (Rhipicephalus sanguineus). After the initial infection, there is a decrease in the platelet count within 7 days post infectionem; the lowest values are reached between days 14 and 24 p.i.
Basophil inclusions (morulae) in the platelets can particularly be detected 7 – 10 days p.i. The phase of bacteremia extends approximately of a period of 4 – 14 days p.i., followed by a phase in which the pathogen cannot be detected in the peripheral blood. Subsequently, these phases alternate cyclically depending on the platelet count. In the bacteraemic phase, the pathogen can be detected in blood samples by means of PCR.
Anaplasma ovis
Anaplasma ovis is a haematogenous bacterium in small ruminants. It is a gram-negative, obligate intracellular, coccoid or pleomorphic bacterium from the order Rickettsiales, which infects erythrocytes. Morphologically, it cannot be distinguished from the closely related Anaplasma marginale.
Anaplasma ovis infection is a vector-borne disease; the pathogen is probably transmitted by ticks of the genus Dermacentor, Rhipicephalus and Hyalomma. Clinical signs include anaemia, anorexia and weight loss.
Both PCR tests (Anaplasma ovis and Mycoplasma ovis) are only available in combination.