Experimental Eperythrozoon ovis infection of sheep

Abstract

Extract

Eperythrozoon ovis is an epi-erythrocytic sheep parasite of uncertain classification with a world-wide distribution (Sutton, 1970 Sutton, R. H. 1970. Eperythrozoon ovis — a blood parasite of sheep. N.Z vet. J., 18: 156–164. [Taylor &; Francis Online] , [Google Scholar]), but whether eperythrozoonosis is a disease of economic importance remains unresolved. In Scotland, Foggie and Nisbet (1964 Foggie, A. and Nisbet, D. I. 1964. Studies on Eperythrozoon infection in sheep. J. comp. Path., 74: 45–61.  [Google Scholar]), found that experimentally E. ovis caused a clinical anaemia, occasionally with jaundice, but there was no significant difference in weight gain between infected and control sheep. Similar observations in naturally infected sheep were recorded in Norway by Overas (1969 Overas, I. 1969. Studies on Eperythrozoon ovis infection in sheep. Acta vet. Scand., Suppl. 28 [Google Scholar]), and in Australia by Harbutt (1969b Harbutt, R. Patricia. 1969b. The effect of Eperythrozoon ovis infection on body weight gain and haematology of lambs in Victoria. Aust. vet. J., 45: 500–504.  [Google Scholar]), Other Australian authors have found infection by this parasite; associated with outbreaks of ill-thrift in lambs (Sheriff et al., 1966 Sheriff, D., Clapp, K. H. and Reid, A. Marjorie. 1966. Eperythrozoon ovis infection in South Australia. Aust. vet. J., 42: 169–176.  [Google Scholar]) and severe anaemia with some mortality (Littlejohns, 1960 Littlejohns, I. R. 1960. Eperythrozoon ovis in sheep. Aust. vet. f., 36: 260–265.  [Google Scholar]; Maxwell, 1969 Maxwell, J. A. L. 1969. Eperythrozoon ovis infection in Western Australia. Ausf. vet. J., 45: 436–436.  [Google Scholar]; Campbell et al., 1971 Campbell, R. W., Sloan, C. A. and Harbutt, R. Patricia. 1971. Observations on mortality in lambs in Victoria associated with Eperythrozoon ovis. Aust. vet. J., 47: 538–541.  [Google Scholar]). Although the presence of strains of different pathogenicity has been suggested (Foggie and Nisbet, 1964 Foggie, A. and Nisbet, D. I. 1964. Studies on Eperythrozoon infection in sheep. J. comp. Path., 74: 45–61.  [Google Scholar], 1966 Foggie, A. and Nisbet, D. I. 1966. Eperyihrozoon ovis. Vet. Rec., 79: 297–298.  [Google Scholar]; Harbutt, 1969a Harbutt, R. Patricia. 1969a. The incidence and clinical significance of Eperythrozoon ovis infections of sheep in Victoria. Ausf vet. J., 45: 493–499.  [Google Scholar]), other factors influencing the disease should also be considered (Littlejohns, 1960 Littlejohns, I. R. 1960. Eperythrozoon ovis in sheep. Aust. vet. f., 36: 260–265.  [Google Scholar]).     

The effects of Eperythrozoon ovis in sheep

Infection of adult sheep with a single strain of Eperythrozoon ovis led to three different situations. First, the animal resisted the organism and no haematological changes occurred. Second, the host developed a controllable parasitaemia in which erythrocyte values fell shortly after peak parasitaemia and then returned to normal. Third, the host failed to control the parasitaemia and chronic low grade anaemia developed. Dexamethasone sometimes caused a resurgence of parasitaemia in sheep.     

绵羊附红细胞体人工感染小鼠模型的建立

分别用绵羊附红细胞体自然感染病羊的全血及分离纯化的绵羊附红细胞体对小白鼠进行攻毒,以建立绵羊附红细胞体人工感染小鼠模型。通过攻毒后症状观察、血液涂片镜检和绵羊附红细胞体特异性PCR检测法,对建立的模型进行评价。结果显示,各试验组小鼠人工感染后3~6 d,血液中均可检测到绵羊附红细胞体,而对照组小鼠未出现异常症状,且血液附红细胞体检查结果为阴性。该研究成功地构建了绵羊附红细胞体小白鼠感染模型,创建的模型可用于附红细胞体的生物学特性、致病机制、药物筛选等方面的研究。     

羊附红细胞体双抗体夹心ELISA诊断方法的建立

为快速准确诊断和检测羊附红细胞体病,及时采取防治措施,建立了检测羊附红细胞体抗原的双抗夹心ELISA诊断方法。选取规模化养殖场羊,镜检附红细胞体红细胞感染率> 90%,无菌采取血液,分离羊附红细胞体抗原,制备纯化兔抗羊附红细胞体抗体,应用辣根过氧化物酶标记抗体,进行双抗体夹心ELISA试验。试验结果表明,双抗体夹心ELISA方法的最佳工作条件为:抗体最佳包被量为82.91 μg/mL,酶标抗体最适工作浓度为1∶400,抗原最低检出量为7.81 μg/mL;而且与支原体、大肠杆菌、葡萄球菌以及牛、猪、兔附红细胞体均不出现交叉反应,表明该方法具有良好的特异性,可用于羊附红细胞体病的诊断和群体检测。     

Humoral immune response of sheep to infection with Eperythrozoon ovis

Circulating antibody was detected by an indirect fluorescent antibody test (IFAT) in the serum of sheep infected experimentally with Eperythrozoon ovis. Antibodies were first detected 15 to 32 days after infection with E ovis and titres peaked at 41 days. This antibody may be associated, at least in part, with protection against infection with E ovis since the initial increase in antibody titre coincided with a fall in the primary parasitaemia. A role for antibody is suggested further by the fact that the prepatent period of infection was prolonged by one day and the parasitaemia initially remained at low levels in infected sheep protected by passively transferred hyperimmune serum. Moreover, following primary infection, acquired immunity was manifest by a lack of parasitaemia following challenge infections while increased IFA titres were observed. No evidence of opsonic activity was observed in an in vitro erythrophagocytosis test in that neither mouse macrophages nor sheep monocytes phagocytosed E ovis infected or uninfected erythrocytes sensitised with hyperimmune serum.     

Observations on the pathology of Eperythrozoon ovis infection in sheep

The main pathological features of experimental Eperythrozoon ovis infection were an increase of spleen weight by up to 250% at the peak of parasitaemia and an increase in liver weight by 36%. Haemosiderin was present in the kidneys, livers and spleens of all infected sheep at the peak and late stages of parasitaemia. Control sheep had haemosiderin in the spleen only. On the basis of these findings, intravascular haemolysis appears to be the predominant mode of red cell removal. Although not observed histologically, some erythrophagocytosis by the spleen and liver probably occurs in the course of the infection.     

Eperythrozoon ovis and copper poisoning as causes of jaundice in lamb carcases

A total of 126 lamb carcases, of which 80 were jaundiced and 46 were grossly normal at routine meat inspection, were examined. Two specific diseases were demonstrated to be associated with jaundiced carcases. Eperythrozoon infection was demonstrated in 65% of jaundiced, and 12% of non-jaundiced carcases from jaundice-affected lots, but not in 5 normal carcases from unaffected killing lots. Copper poisoning was demonstrated in 2 of the jaundiced carcases. Infection with Eperythrozoon ovis was therefore the condition most commonly associated with, and presumably the major cause of jaundice in these lamb carcases. Copper poisoning was a less common cause of jaundice.     

Role of the spleen and rosette-formation response in experimental Eperythrozoon ovis infection

The role of the spleen and rosette-formation responses was investigated in sheep experimentally infected with Eperythrozoon ovis. Phagocytic activity was observed in the spleen 19 days after primary infection. Phagocytosis of E. ovis-parasitised and non-parasitised erythrocytes by cordal reticular cells occurred. E. ovis organisms seemed to be detached from the erythrocytes by pseudopodia extending from macrophages and cordal reticular cells without causing damage to the plasmalemma of the erythrocyte. No phagocytic activity was observed in spleens removed 74 and 146 days after infection. Antigen-specific lymphoid cell responsiveness, assessed by rosette formation, indicated that 2.8, 15.4, 8.0 and 6.0% of lymphoid cells in the spleens of the four E. ovis-infected sheep, respectively, formed antigen-specific rosettes. Rosette formation did not occur when splenic lymphocytes from E. ovis-infected sheep were mixed with non-infected erythrocytes or when splenic lymphocytes from an uninfected sheep were used.     

羊附红细胞体病PCR检测方法的建立

根据羊附红细胞体的16S rRNA基因参考序列，设计1对特异性引物．建立了检测羊附红细胞体的PCR技术。用本方法从感染血样中特异扩增出1条预期大小为1169bp的片段。该方法灵敏、快速、特异性高．可用于羊附红细胞体病的早期快速诊断和流行病学调查。