Maternal antibody-mediated elimination of a Puumala hantavirus outbreak in a bank vole colony

Bank voles (Myodes glareolus syn. Clethrionomys glareolus) are frequently used as an animal model in ecological and biomedical studies, and are important reservoir of viral and bacterial zoonotic pathogens, e.g. of Puumala hantavirus (PUUV). Here we describe an accidental PUUV outbreak in a large bank vole laboratory colony by incursion of infected wild-trapped bank voles, and a successful eradication of the virus. The eradication plan was based on results of previous studies, which showed that maternal antibodies (MatAb) protect the young from infection for up to 40 days after the weaning, four weeks longer than the estimated duration of maintaining infectivity of PUUV in the environment. After ensuring that most animals are infected, 620 pairs were mated on the same day. Only females that showed PUUV-specific antibodies and gave offspring within 26 days after the mating were retained. All individuals of the parental generation were euthanized before the last weaning. The weaned offspring was moved to individually ventilated cages (IVC) and repeatedly tested for the presence of PUUV-specific antibodies and RNA. A few infected and suspicious animals were euthanised. Then the animals were mated (in IVC) and after producing grand-offspring euthanised and tested for PUUV RNA in lungs. No PUUV RNA was detected, and no animals showed PUUV-specific antibodies in next generations. The successful clearance confirmed the protective efficiency of PUUV-specific MatAb. The procedure for clearance of PUUV in the bank vole colony may represent a blueprint for similar approaches in precious colonies of other rodents infected by similar pathogens. Author SummaryIn 2006 we started a unique long-term experiment on the bank vole, a common European rodent. Our goal was to study how animals can adapt to different challenges - a process called adaptive radiation. We established 16 vole lines: four control lines and others selected for specific behavioural and physiological traits. Over the years, this colony became an important model for studying evolution, physiology, and behaviour. Unfortunately, the colony became infected with Puumala hantavirus. The virus is mild for voles but can cause serious zoonotic illness in humans, without specific medical treatment available. At first, it seemed that the entire colony would have to be destroyed - a loss of thousands of animals and many years of research. However, we used a natural advantage: young voles born to infected mothers are temporarily protected by maternal antibodies. By carefully planning breeding, isolation, and testing, we created conditions where the virus lost its strength before the young lost their protection. This simple yet challenging approach worked - we saved the colony. Because many animals respond to viruses in a similar way, our method can help rescue other valuable research populations without complex procedures like embryo transfer or cross-fostering.