A review Study on Potomac Horse Fever

Potomac Horse Fever (PHF) is an acute enterocolitis syndrome causing mild colic, fever and diarrhea in all life stages in horses. It is also responsible for abortion in pregnant mares. The agent of PHF was diagnosed as Neorickettsia risticii. PHF was first diagnosed as a livestock disease, by veterinarians in Maryland State of USA in horses living around Potomac River. Since, most of the cases of disease were recorded in July, August and September, then it was regarded as a seasonal disease. Later studies revealed that a trematode vector takes the role as a vector for transmission. Routine cell culture and PCR were used for clinical diagnosis of the PHF. Using indirect fluorescent antibody tests revealed positive cases in most places of Canada and America, which regarded as former contacts with the agent of disease. Neorickettsia risticii could not be seen in monocyte in prepared blood smears from clinical cases of horses and this is contrary to Anaplasma phagocytophilum which very easily seen in granulocytes of blood in infected horses. Neorickettsia risticii has been isolated from released trematodes from fresh water snails. PHF is not a contagious disease and infected horses could be kept near susceptible horses. PHF is not regarded as a zoonosis. It is concluded that related veterinarians to horse industry in Iran should be informed about the possible occurrence of disease.