Evaluation of sequential coinfection with Anaplasma phagocytophilum and Anaplasma marginale in cattle.
OBJECTIVE
To determine whether sequelae of infection differed among single versus double infection with Anaplasma phagocytophilum or Anaplasma marginale, with and without tick salivary extract, in cattle.


METHODS
Eighteen 13-month old steers.


METHODS
Treatment groups of 3 cattle each included A marginale inoculated ID followed on day 35 by A phagocytophilum without tick saliva, A phagocytophilum followed on day 10 by A marginale without tick saliva, A marginale followed on day 35 by A phagocytophilum with tick saliva, A phagocytophilum followed on day 10 by A marginale with tick saliva, tissue culture control injection, and tick saliva control injection. Infection was monitored via clinical observations, CBC, serologic testing, and PCR analysis of blood and tissues.


RESULTS
Infected cattle had significantly reduced weight gain. Anemia occurred 25 to 32 days after A marginale infection, which was attenuated by tick saliva. Parasitism was greater if cattle had not previously been inoculated with A phagocytophilum. Nine of the 12 treated cattle had positive results of PCR analysis for A phagocytophilum from at least 1 blood sample. Five tissue samples had positive results of PCR analysis for A phagocytophilum; PCR results for A marginale were positive in spleen, lung, lymph node, heart, and ear skin of infected cattle.


CONCLUSIONS
Results indicated an important biological interaction between A marginale and A phagocytophilum infection as well as with tick saliva in disease kinetics and severity in cattle, which may be important for interpretation of diagnostic tests and management of disease in areas where both pathogens occur.
Hoar
Bruce R
BR
Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Nieto
Nathan C
NC
Rhodes
Diane M
DM
Foley
Janet E
JE