EPIDEMIOLOGY OF INFECTIOUS HEMATOPOIETIC NECROSIS, VIRAL HEMORRHAGIC SEPTICEMIA, AND KOI HERPES VIROSIS IN AQUACULTURED FISH IN THE REPUBLIC OF NORTH MACEDONIA

Abstract

This doctoral dissertation investigates the epidemiology of three significant viral diseases affecting cultured fish in the Republic of North Macedonia: Infectious Hematopoietic Necrosis (IHN), Viral Hemorrhagic Septicemia (VHS), and Koi Herpesvirus Disease (KHVD). The research was conducted from 2020 to 2024, analyzing samples from 57 trout farms and 36 carp farms. Advanced molecular techniques (RT-qPCR), genetic typing of isolates, histopathological analyses, and statistical models for assessing risk factors were employed. The analyses revealed that VHS and KHVD were not detected in any of the tested samples, confirming the country's disease-free status regarding these infections. In contrast, a concerning trend was noted regarding the spread of IHN among trout farms. The number of farms infected with IHN increased from two cases in 2018 to 36 in 2024. Genetic analysis revealed that all IHN isolates belong to the MAKIHNV1 genotype, exhibiting minimal genetic variation of less than 1.5%. This indicates a common infection source or limited viral evolution within the studied population. Histopathological examinations of IHN-positive fish revealed significant damage to the gill lamellae, kidney tissue degeneration, and inflammatory changes in the liver, confirming the virus's detrimental impact on fish health. Statistical analysis identified that the most significant risk factor for the spread of IHN was the purchase of live fish, particularly when farms relied on a single supplier. The frequency of purchases and the number of suppliers also significantly influenced the infection rate. Although biosecurity measures such as equipment and vehicle disinfection showed no significant impact on infection reduction, access control and quarantine implementation proved critical in preventing disease spread. These findings confirm the disease-free status for VHS and KHVD in the country but highlight an urgent need to strengthen biosecurity measures and monitoring to control IHN. The research emphasizes the importance of strategic management approaches in fish farms, including strict quarantine protocols upon fish introduction and enhanced biosecurity systems. This study provides vital epidemiological information on viral diseases in aquaculture and offers guidelines for reducing the risk of IHN in fish farming operations.