Clinical and pathological investigation of Maedi-visna outbreak in a farm from Bulgaria

In the autumn of 2024, an outbreak of Maedi-visna (MV) was identified in Bulgaria in the village of Sigmen, Burgas district. The disease is a slowly progressive, persistent, usually subclinical viral infection in sheep, distributed worldwide. Difficulties in early diagnosis are the long period between infection and the dynamics of the antibody titer (seroconversion), the emission of an infectious onset without clinical signs, the lack of vaccines, as well as some ongoing misunderstandings in the epidemiology and the transmission mechanisms, which determine the complex nature of the disease.

The aim of our study is to follow the development of the outbreak, clinical and pathological findings.

The Number and Surveillance Data of Small Ruminants in Bulgaria. We used data from agro-statistics of the Ministry of Agriculture and the Register of animals for 2023. To visualize the data, we constructed a map and a chart.Clinical examination of the herd. Necropsy. In total, 5 fresh carcasses were submitted for necropsy. Carcasses were necropsied according to standard guidelines for post mortem examination at the National Research Diagnostic Veterinary Medical Institute. Samples were collected in sterile containers in compliance with all biosafety and biosecurity requirements.

During our examination, we have observed neurological symptoms including a head tilt, shaking their head back and forth, altered mentation, they eat their fur, do not chew with their mouth full, or chew with their mouth empty; poor quality of the wool. Atypically emaciated, especially those of the Ile de France breed. Many of the animals are lethargic, depressed, lying down, have difficulty standing up and moving. The necropsy shows bilateral hemorrhagic pneumonia, an enlarged heart, with gelatinous edema of the pericardium. Macroscopic lesions of progressive pneumonia are confined to the lungs.

Maedi-visna infection in sheep is widespread throughout the world. The occurrence of this outbreak in our country shows that the virus is present in the field. The lack of a national program obliging farmers to test their animals leads to a high risk of the spread of MV in Bulgaria. Our investigation highlights the need for more systematic studies using a consecutive testing strategy.