Scientists have a poor understanding of the epidemiology of Borna disease virus (BDV). The disease is primarily known for infecting horse and sheep, yet the virus does not seem to be transmitted directly between diseased animals. Another animal reservoir is thus implicated. The method of transmission is also unknown.
Sander and Staehli sought to develop an animal model that explains the epidemiology of BDV in horse and sheep. They used persistently infected rats, which are infected as newborns and consequently have lifelong infection but with an absence of any disease. Unlike in rats infected as adults, where virions are found only in the central and peripheral nervous system, the persistently infected rats have virus in almost all tissues of their body and in bodily secretions.
Cohousing persistently infected rats with naïve rats, the researchers were able to determine the following:
• Confirmation of transmission between naïve and persistently infected rats due to cohabitation
• Brief contact is insufficient for transmission, but cohabitation for 1-2 days is enough
• By varying times that rats were sacrificed for immunohistochemical analysis of the brain, BDV appears to be transmitted through an olfactory route
o Infected cells are primarily in the olfactory bulb and the olfactory cortex, and then spreads to the hippocampus via fornix, septum, and ventral hippocampal commissure
• Using titers, urine is strongly implicated as being a primary method of transmission
o Urine must be fresh for transmission
The study provides an alternative to the popular view that BDV is transmitted from infected horse or sheep, namely suggesting that rats, especially those with a persisteny infection, may contaminate animal feed and spread the disease to farm animals or humans. The researchers call for further study of the prevalence of virus in rats, and assessment of biological safety requirements for those working with persistently infected rats in the laboratory.