As SARS-CoV-2 reminded everyone, there are lots of undiscovered viruses out there, and some of them can cause disease in humans, animals, or both. It’s not very hard to find a new virus, actually. Figuring out what it means is often the challenge, because simply finding a virus in a sick person or animal doesn’t mean that virus is the cause of the illness. Our bodies contain many completely harmless viruses, and viral discovery is one field in which information advances much more rapidly than knowledge.
A new feline virus was found during investigation of an outbreak of vomiting and diarrhea in cats three animal shelters in British Columbia (Canada) between Nov 2018 and Jan 2019 (Li et al. Viruses 2020). The outbreak started with vomiting and diarrhea in 8 of 12 cats in the adoption room of one shelter (Shelter 2). The first affected cats had come from another shelter (Shelter 1) and were sick around the time of transfer. Upon further investigation, they found 11 sick cats at Shelter 1. Then, they found 13 affected cats at Shelter 3, after a cat from Shelter 2 was transferred there (see image below). No clear method of transmission was apparent, as most affected cats had not been housed with another (known) affected cat.
They did a very nice job of contact tracing (which is often very difficult in a shelter situation) and characterizing the disease. It was estimated the incubation period could have been as short as 24 hours, and as long as 5-7 days. Vomiting usually started 1-2 days before diarrhea, and the median duration of illness was 4 days.
Usually, outbreaks like this aren’t investigated too carefully because of cost and the low likelihood that something relevant will be found. Here, they used sequence-based methods to sequence all the viral bits found in fecal samples from the cats. This makes it possible to assemble most or all of the genomes of a range of viruses that are present. In doing so, they found a new virus, which they named “fechavirus”, in 8/17 affected cats. It is a type of chapparvovirus, and genetically it’s most closely related to canine cachavirus (a fairly recently discovered virus of questionable relevance). They also found three different bocaviruses in 9/17 cats. Other testing was unremarkable – a few different potential causes of gastrointestinal disease were found in some cats, but nothing convincing.
Based on the timing of infection and disease, the investigators suspected that this new virus was the cause of the outbreak, but the hard part is confirming it. Finding a new virus is much easier than figuring out its clinical relevance, and that can take time. Various “new causes of disease” have been found in many different species, but many are subsequently determined to be only minor players or irrelevant, so we should take this report as an indication to study this virus further. The fechavirus was found in less than 50% of the affected cats. We don’t expect to find the causative pathogen in all affected individuals during an outbreak, but this rate of detection raises more questions. Maybe it’s because the virus isn’t shed for very long by affected animals. Maybe it’s because the testing isn’t very sensitive. Maybe it’s because it wasn’t actually the cause of the illness and it was just an incidental finding.
Importantly, there was no study of healthy cats in the shelters or otherwise to test how commonly fechavirus is found in the general cat population. So care needs to be taken to not over-interpret the results. (Anyone remember canine circovirus? It got lots of attention (to the point of paranoia) when it was found in sick dogs, but we eventually figured out it’s a minor pathogen, at best).
The big questions…..
Is this virus an important, emerging cause of disease in cats?
Is it a rare virus that can cause sporadic severe disease?
Is it a virus that can contribute to disease only when another infection is present?
Is it a harmless virus that’s common in healthy cats and was found incidentally?
Time (and study) will tell, but it’s still important to know about these “new” viruses so we know what to investigate.