Anaplasma & Ehrlichia spp.
Anaplasmosis is a disease caused by intracellular bacteria infecting specific white blood cells, the so-called neutrophil granulocytes. The disease is prevalent in the US, where the causative pathogen is transmitted by the tick species Ixodes scapularis. In Europe, anaplasmosis is rarely documented. However, it may be found in several countries such as France and Slovenia, when it is actively searched for. In Switzerland, no disease case has been documented so far.
Various species of the genus Anaplasma occur worldwide; they are mainly known as pathogens in animals. In Switzerland, Anaplasma phagocytophilum (formerly Ehrlichia phagocytophila and E. equii) occurs as a tick-borne pathogen in cattle and horses. Unlike the other species of the genus Anaplasma, A. phagocytophilum parasitizes leukocytes and not erythrocytes. Anaplasma spp. belong to the order Rickettsiales, which also includes the genera Rickettsia and Ehrlichia.
Anaplasmosis was first described in California in 1969.
In a first seroepidemiological study in Europe, a seroprevalence of 17% in humans was found for Switzerland (Brouqui, Dumler, Lienhard et al,1995). A first European case of anaplasmosis was subsequently described in Slovenia in 1997. Further cases have been documented in many European countries, including France (Alsace); however, no cases have yet been documented in Switzerland.
In Europe, Anaplasma phagocytophilum is transmitted primarily by the tick species Ixodes ricinus. This tick species also transmits several other important pathogens, such as Borrelia burgdorferi and tick-borne encephalitis virus. The prevalence of Anaplasma phagocytophilum in Ixodes ricinus ticks varies in different countries in Europe; in Switzerland it is estimated at 1.7% (2019).
In the US, anaplasmosis is common in the northeastern and central-northern regions toward Canada (>13 cases per million population). In the US, the causative agent of anaplasmosis is mainly transmitted by the tick species I. scapularis and I. pacificus. Anaplasmosis can therefore also occur in travelers returning from these endemic areas (see CDC distribution maps for I. scapularis and I. pacificus).
The majority of infections with Anaplasma phagocytophilum are asymptomatic. In symptomatic infections, nonspecific flu-like symptoms may occur, such as fever, headache, myalgia, arthralgia, nausea, vomiting, and diarrhea. Exacerbation of symptoms is rare; however, some patients may develop respiratory symptoms (interstitial pneumonia, atypical pneumonia, and even ARDS) or skin manifestations (rash, exanthema). Neurological manifestations ( vertigo, facial paralysis, meningitis) are very rare.
The standard of treatment remains the same as for most tick-borne diseases, especially intracellular bacteria: Doxycycline PO or IV.
There is no protective vaccination to protect against anaplasmosis.
The standard method for detecting acute infection is direct pathogen detection in a blood smear stained with Giemsa. This involves the detection of an aggregated cell mass in the cytoplasm of granulocytes. However, this simple detection method has a low sensitivity, which is why pathogen detection by PCR is preferred in routine diagnostics. ADMED Microbiology provides an “Ehrlichia” PCR for the detection of Ehrlichia spp. and Anaplasma spp. Confirmatory diagnostics are subsequently performed at the CHUV, Laboratoire de Microbiologie. PCR can be performed from various infected tissues, mainly EDTA blood samples, punctates and biopsies are suitable.
The serology method validated and previously used in the ADMED laboratory is no longer available; a new test is currently being validated. It must be noted, however, that serology should only be performed if a corresponding suspect diagnosis has been established. Serology should not be performed if the pre-test probability is low. The detection of a fourfold increase in titer immediately after the acute phase of the disease is useful.
- Matei IA, Estrada-Peña A, Cutler SJ, Vayssier-Taussat M, Varela-Castro L, Potkonjak A, Zeller H, Mihalca AD. A review on the eco-epidemiology and clinical management of human granulocytic anaplasmosis and its agent in Europe. Parasit Vectors. 2019 Dec 21;12(1):599. doi: 10.1186/s13071-019-3852-6.
- Brouqui P, Dumler JS, Lienhard R, Brossard M, Raoult D. Human granulocytic ehrlichiosis in Europe. Lancet. 1995 Sep 16;346(8977):782-3. doi: 10.1016/s0140-6736(95)91544-3.
- Pilloux L, Baumgartner A, Jaton K, Lienhard R, Ackermann-Gäumann R, Beuret C, Greub G. Prevalence of Anaplasma phagocytophilum and Coxiella burnetii in Ixodes ricinus ticks in Switzerland: an underestimated epidemiologic risk. New Microbes New Infect. 2018 Sep 6;27:22-26. doi: 10.1016/j.nmni.2018.08.017.