Anaplasma spp

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Anaplasma marginale within bovine erythrocytes, visualised under light microscopy

Anaplasma spp are a rickettsiales (family Anaplasmataceae) bacteria which causes anaplasmosis (tick-borne fever)[1], anaemia and abortion in cattle. Anaplasmosis is of significant economic concern to the beef and dairy cattle industries.

Found in tropical and subtropical regions worldwide, Anaplasma species are obligate intraerythrocytic parasites of cattle. Common species which cause disease include:

  • A. marginale - worldwide[2]
  • A. centrale - mild disease[3]
  • A. phagocytophilum (formerly Ehrlichia phagocytophilum & E. equi) - non-pathogenic[4]
  • A. platys (previously E. platys)

Anaplasma spp are transmitted to cattle via insect vectors, primarily ticks including Rhipicephalus microplus (formerly Boophilus microplus), Dermacentor spp, Ixodes spp, Hyaloma spp and Ornithodorus spp. The bacteria circulate within cattle blood, do not cross the blood-brain barrier but may cross into the placenta, allowing vertical transmission and birth of infected calves[5]. A. marginale and A. phagocytophilum can also cause persistent infection in adult cows[6].

Mechanical transmission by contaminated needles, during dehorning and by Culicoides spp midges and some other biting flies is believed to also occur.

Anaplasmosis may also be spread through the use of contaminated needles or dehorning or other surgical instruments.

Clinical signs

Clinical signs appear to correlate with the duration of exposure and cattle breed (Bos indicus relatively resistant)[7]. Young calves are often subclinically infected unless coinfected with other diseases such as bovine viral diarrhoea or infectious bovine rhinotracheitis. Anaplasmosis usually manifests in cattle over 1 year of age and can be fatal in aged cattle.

Signs are related to erythrocytic phagocytosis, and anaemia is a common presenting signs. Fever, dyspnea, depression, lethargy, anorexia and recumbency are also observed in acutely affected cattle. Pregnant cows may abort. Haematological tests reveal a regenerative hypochromic, macrocytic anaemia. Icterus is often a terminal sign.

In contrast to Babesia spp infections, haematuria and hemoglobinuria are rarely observed.

Diagnosis

Diagnosis is based on circumstantial evidence of clinical signs referable to tick-borne fever, supported by laboratory identification of intraerythrocytic parasites. Identification of Anaplasma spp in the laboratory can be confirmed by use of light microscpy using Giemsa staining, supported by ELISA, complement fixation and card agglutination. Serological cross-reactivity appears to be common and PCR testing is required for definitively establishing speciation of parasite[8].

Treatment

Tetracyclines, enrofloxacin[9] and imidocarb are the drugs of choice for anaplasmosis in cattle. New infections may occur after 8 - 12 months.

Tick control is essential to preventing further outbreaks, and drugs such as doramectin, ivermectin and fipronil have proven effective.

Subunit vaccines have been tested experimentally in cattle but do not appear effective at preventing anaplasmosis[10].

References

  1. Nieder M et al (2012) Tick-borne fever caused by Anaplasma phagocytophilum in Germany: first laboratory confirmed case in a dairy cattle herd. Tierarztl Prax Ausg G Grosstiere Nutztiere 40(2):101-106
  2. Shebish E et al' (2012) Prevalence and molecular detection of Anaplasma marginale, Babesia bovis and Babesia bigemina in cattle from Puntarenas Province, Costa Rica. Vet Parasitol 188(1-2):164-167
  3. Aktas M et al (2012) A survey of ixodid ticks feeding on cattle and prevalence of tick-borne pathogens in the Black Sea region of Turkey. Vet Parasitol 187(3-4):567-571
  4. Zhang L et al (2012) Anaplasma phagocytophilum Infection in Domestic Animals in Ten Provinces/Cities of China. Am J Trop Med Hyg 87(1):185-189
  5. Pypers AR et al (2011) Fatal congenital anaplasmosis associated with bovine viral diarrhoea virus (BVDV) infection in a crossbred calf. J S Afr Vet Assoc 82(3):179-182
  6. Brown WC (2012) Adaptive immunity to Anaplasma pathogens and immune dysregulation: implications for bacterial persistence. Comp Immunol Microbiol Infect Dis 35(3):241-252
  7. Chávez AS et al (2012) Expression patterns of Anaplasma marginale Msp2 variants change in response to growth in cattle, and tick cells versus mammalian cells. PLoS One 7(4):e36012
  8. Al-Adhami B et al (2011) Serological cross-reactivity between Anaplasma marginale and an Ehrlichia species in naturally and experimentally infected cattle. J Vet Diagn Invest 23(6):1181-1188
  9. Facury-Filho EJ et al (2012) Effectiveness of enrofloxacin for the treatment of experimentally-induced bovine anaplasmosis. Rev Bras Parasitol Vet 21(1):32-36
  10. Lasmar PV et al (2012) Evaluating the effectiveness of an inactivated vaccine from Anaplasma marginale derived from tick cell culture. Rev Bras Parasitol Vet 21(2):112-117