Emerging infectious diseases comprise a substantial fraction of important human infections, with potentially devastating global health and economic impacts. A 2008 paper in Nature described the emergence of no fewer than 335 infectious diseases in the global human population between 1940 and 2004.
In the veterinary field, just as in the medical field, advanced molecular techniques and sophisticated computer-based algorithms for genetic sequence assembly and analysis have revolutionized infectious disease research. They have also raised important questions, as the potential pathogenic role of novel viruses can be difficult to determine.
Novel viruses may contribute to causes of feline morbidity and mortality
What is well understood is that novel viruses may contribute to diseases that are major causes of feline morbidity and mortality, including cancer and chronic kidney disease (CKD). A state-of-the-art review article published in the Journal of Feline Medicine and Surgery this month focuses on two novel viruses that have the potential to negatively impact feline health and welfare globally — gammaherpesvirus and morbillivirus.
For many years, domestic cats were identified as the natural host for just a single herpesvirus, feline herpesvirus 1, which is a common cause of ocular and upper respiratory tract disease. In 2014, a targeted virus discovery programme, prompted by the clinical observation that cats develop the types of cancer that, in humans, are caused by gammaherpesviruses, identified Felis catus gammaherpesvirus 1 (FcaGHV1).
The first gammaherpesvirus known to infect domestic cats
The first gammaherpesvirus known to infect domestic cats, FcaGHV1 is widely endemic; studies suggest that cats can be infected from 2 months of age, and that most adult cats are persistently infected. What is not yet known is whether FcaGHV1 has any pathogenic role in cats. Comparative evidence, however, suggests that while gammaherpesvirus infections typically remain subclinical, in certain circumstances, often after many years of infection, they can cause severe and frequently fatal disease.
While many emerging diseases in humans originate in animals, there is no known zoonotic risk associated with these two viral infections. Limited transmission between felids is known to be possible, at least for gammaherpesviruses, with infection of critically endangered Tsushima leopard cats with FcaGHV1 recently having been identified in Japan.
Technological advances mean that the rate at which novel viruses are being discovered now exceeds our understanding of their clinical relevance. The authors conclude that deciphering the impact of these viruses in cats will require multiple lines of investigation, and the practising veterinarian has an important role to play.
Ultimately, the identification of new viral pathogens is not all bad news for cats, as it raises the prospect of improved patient outcomes through specific treatment and, more significantly, disease prevention through viral control measures.