Ovine anaplasmosis in Northwest China

Abstract

This paper described studies on the distribution, vector and multiplication of the pathogen of ovine anaplasmosis and a complement fixation test (CFT) for the disease.Anaplasma ovis was found to be widely distributed in Northwest China and the infection rate of sheep and goats was very high. From 1986 to 1991, 2,813 sheep and goats were examined for the pathogen and by CFT. The results indicated thatA. ovis was distributed in 44 counties in Gansu province and the infection rate was 30·1–60·8%; while the infection rate in West Inner Mongolia, East Qinhai, North Shaanxi and East Ningxia was 44·3%, 10–56·6%, 20–30% and 21·3–39·1% respectively. The organism caused anaemia and subclinical symptoms in indigenous sheep and goats in the areas mentioned above. The only exception was Ejinaqi in Western Inner Mongolia, where the morbidity of sheep and goats was as high as 40–50% and the mortality was 17%. Experimental transmission demonstrated thatDermacentor nuttalli, Hyalomma asiaticum kozlovi andRhipicephalus pumilio could transmitA. ovis to sheep or goats through transient infestation when moving from host to host. Neither transovarial nor transstadial transmission was observed. Splenectomized goats were susceptible to the pathogen and the later was seen in blood films 18–35 days after infestation with adult ticks ofD. nuttalli. The peak parasitemia of erythrocytes was 18–55·3%. When the goats were infested withHy. asiaticum, the potential incubation period was 34–36 days and parasitaemia reached 48·3–53·5%. The main symptoms were anaemia, jaundice and leanness; mortality was 6/8. The organism was infective to goats after 925 days preservation in liquid nitrogen. Preparation of antigen and CFT were also studied. When splenectomized sheep or goats were infected by inoculation ofA. ovis stabilates, the pathogen multiplied rapidly and the parasitemia reached 69·6–71·3% within 9–12 days. If the sheep or goats were treated with Dexamithasone, parasitaemia could reach as high as 97·5%. Ten artificially and ten naturally infected sheep and goats were examined by CFT and all of them were positive. Antibodies could be detected five days after infection and reached a peak on day 15. The titre gradually decreased 45 days after infection, but antibodies could still be detected on day 110. Treatment of sick sheep or goats with oxytetracycline was effective at a dose of 30mg/kg, given once or twice. The curative ratio was 80%.