Cat colonies present some interesting infectious disease challenges. Anytime we have animals congregating, there’s an increased risk of disease transmission, and when they’re outside, it also increases the risk of diseases from wildlife. Thus cat colonies can become a bridge for diseases between wildlife and people.

I’ll pause here to add a perspective that I’d often put at the end of the post, and which people often miss (and then email me asking why I hate cats or cat colonies or people who manage cat colonies). I have no issues with cat colonies. Yes they create some risks, but life is full of risks. I’m writing this with a formerly completely feral cat curled up beside me. Yet we should neither ignore nor dismiss issues with cat colonies, but rather try to optimize the cat health and human health components as much as possible.

Back to rabies and cat colonies…

Rabies is always a concern in cat colonies. Any outdoor cat in a rabies endemic area has a risk of encountering rabies from a bat or other reservoir species (e.g. raccoon, skunk, fox). Colonies just amplify the potential impacts: a solitary rabid cat poses much less risk than a cat that has close contact with a large group of other cats, and if it’s a managed colony or the colony cats have other contacts with people, then the risk to humans increases as well. Vaccination of colony cats is a great control measure. It’s hard to get them all, but getting vaccine coverage in a large percentage of the cats will greatly reduce the risk, including to those that can’t be caught. But this method (trap-vaccinate-release (TVR)) takes time and money and people, which are not always available.

Some cat colonies are managed, meaning there are people who attempt to capture and spay/neuter and/or vaccinate the cats, feed them, keep an eye on them and interact with them regularly. In contrast, some colonies are unmanaged – they’re basically just a group of cats that live amongst people. They’re less likely to be the target of spay/neuter and vaccination efforts, and health issues are less likely to be spotted.

A recent report in Morbidity and Mortality Weekly Report (MMWR) about a rabies outbreak in an urban unmanaged cat colony in Maryland highlights some of the issues with these populations. It started with a rabies diagnosis in an aggressive cat that was part of an unmanaged group of about 20 cats. This particular cat was caught and tested because it had bitten or scratched 2 people. Because it’s hard to know who else might have had contact with a feral / unowned cat, they had to go searching for other potential human contacts. A complicating factor here was that the cats were near a hotel, and there was concern that hotel guests might have been exposed. Persons experiencing homelessness in the area were also a concern. So, this was a lot more complicated than many investigations. They had to coordinate with health departments in the US and Canada to track down hotel guests, who were asked if they had any exposure to cats during their stay. Reverse 911 messaging was also used, whereby all local cell phone subscribers got a text that described the situation and what to do. Community-based support programs for individuals experiencing homelessness were engaged to reach other potentially exposed people. They also contacted local healthcare facilities to have them flag people coming in for recent animal bites or scratches.

The investigation was wide reaching. Risk assessments were completed for 197/309 hotel guests from 27 US states and Canada (that’s pretty impressive). In the end, three potentially exposed individuals were identified, all of whom started rabies post-exposure prophylaxis (PEP) within 10 days of exposure (also impressive).

A kitten from the colony was seen to have been acting abnormally around the same time, raising concerns about the potential for a cluster of rabies cases within the cat population. It’s not clear whether the kitten was caught and tested, but it seems like it wasn’t. That’s not too surprising as a sick feral cat can be hard to find and catch. If it had neurological disease from rabies, it wouldn’t have survived more than a few days, so it may have died before anyone could find it.

Three other cats from the colony were caught, euthanized and tested. It’s not clear if they were sick or why these three particular cats were tested, but it sounds like they just wanted to catch and test whichever cats they could (not a great strategy). All three cats were negative for rabies.

Rabies vaccination of feral cats living in close proximity to people takes time and money, but so does an investigation like this. Estimates of personnel time required from just 17 of the 29 jurisdictions involved totaled 450 hours. Three people got PEP, which typically costs thousands of dollars per person in the US. The CDC has estimated that approximately $33 million is spent annually in the US on PEP for people exposed to potentially rabid cats. That would buy a lot of rabies vaccine for cats.

Vaccination and better management of colonies won’t eliminate rabies or drop all the costs to zero. However, like most things with infectious diseases, there’s a cost savings argument to be made for putting more resources into prevention via cat colony vaccination and monitoring. Ideally, we’d have effective oral rabies vaccines, like we do for wildlife, to make it easier to vaccinate large numbers of cats. However, conventional trap, vaccinate and release (TVR) approaches can still achieve good population-level vaccine coverage in these groups. Education of people about interacting (or more specifically, not touching) feral cats, and reporting any bites or scratches from feral cats promptly is also important.

Cat colonies aren’t going away, but with good spay/neuter and TVR programs, they can be managed to reduce the risks to both cats and people.