Epidemiology of Epizootic Lymphangitis of cart horses in Northern Ethiopia Using Conventional diagnostic Methods and Nested Polymerase Chain Reaction

Abstract

Background: Epizootic lymphangitis (EL), caused by Histoplasma capsulatum variety farciminosum (HCF) is a contagious chronic disease of equines characterized by development of nodular lesions in the lymph nodes, lymphatic vessels and skin. This disease is the most important diseases of equines in Ethiopia causing a significant economic loss, particularly cart pulling equines. Todate there is no sound diagnostic nor control measure implemented in the country. Furthermore, there is a shortage of data on the epidemiology of the disease in different regions of the country including northern Ethiopia. This study was conducted to investigate the epidemiology of EL in northern Ethiopia using the conventional methods and the nested polymerase chain reaction (PCR). Methods: A total of 191 cart-horses were enrolled and used as sources of pus and blood samples. The blood was used for the extraction of the DNA of HCF from buffy coat for nested PCR while the pus samples were cultured on Sabourauds Dextrose Agar for isolation. Statistical Package for Social Sciences (SPSS) version 21 was used for data analysis by applying logistic regression, receiver operating characteristic (ROC) curve and Cohen’s kappa coefficient test. In addition, the level of agreement between the clinical examination and the nested PCR was evaluated. Results: Infection with HCF was confirmed in 44% (84/191) of the horses using nested PCR. Subclinical infection was observed in 18.18% (22/121) of the apparently healthy horses. Considering nested PCR as a gold standard, the sensitivity and specificity of the clinical examination were 74% and 95%, respectively while the area under the ROC curve (AUR) was 0.83 (95% confidence interval, 0.77, 0.896). Moreover, a moderate (k=0.675) agreement was observed between the nested PCR and clinical examination.Conclusions: The findings of the present study showed the wide spread occurrence of EL in northern Ethiopia and the advantage of the nested PCR in detecting of the infection of HCF even before the clinical symptoms are apparent.