Boil water advisories: What to do with dogs?
Here's a reader's question: "Our local water authority here on the East Bay of RI has issued a "boil water" alert because of the presence of e-coli as found in a routine test. My question is: Do we need to boil dogs' and cats' drinking water as well? Seems that they eat the worst stuff and may have stronger systems? I gave my dog boiled water at home but then at day care they did not boil the water. "
There’s not a clear answer to this question. Ingestion of bacteria is not necessarily a bad thing. In fact, we ingest huge numbers of bacteria every day. Some dogs (like my dog that eats anything she finds outside) ingest more, and usually no problems develop. Boil water advisories are usually enacted based on detection of E. coli as an indication of fecal contamination. While many (or most) E. coli are harmless, the fact that fecal bacteria are present means that other potentially harmful microorganisms that can be found in feces may also be present. This includes E. coli O157 and Cryptosporidium.
What is the risk for dogs? It’s hard to say. E. coli O157 can cause infection in dogs but this is rare. Dogs that ingest E. coli O157 might shed the bacterium in their stool and potentially infect people. That’s a concern but it’s rare as well. Cryptosporidium is not an important cause of disease in dogs. So, when we look at the highest profile microorganisms in people, the risk to dogs is pretty low. However, we don’t know much about waterborne disease in dogs and it’s certainly possible that other microorganisms could cause disease and that dogs could act as an indirect source of infection of people (i.e. water to dog to person).
So, what should we do during a boil water advisory? I’d probably give my pets boiled water, since I’d be doing it for myself already. It’s not hard to boil a little more water for my pets. Is it really necessary? Who knows? Probably not, but it’s a pretty easy thing to do to reduce any risks that might be present.
It’s never a bad idea to err on the side of caution.
HIV/AIDS, kids and pets
The Centers for Disease Control and Prevention (CDC) has released updated Guidelines for the Prevention and Treatment of Opportunistic Infections Among HIV-exposed and HIV-infected Children. A small but still important part of this document involves recommendations for contact with animals. It's a nice, balanced document that acknowledges the risk but doesn't make unnecessarily restrictive recommendations.
Among the important recommendations regarding animals:
- When getting a new pet, avoid dogs and cats less than 6 months of age or strays: These animals are at higher risk for shedding various infectious diseases and are more likely to have problems with biting and scratching.
- Avoid contact with animals that have diarrhea.
- Wash hands after handling pets.
- Avoid contact with pet feces.
- Avoid contact with reptiles, chicks and ducklings: These are very high risk for Salmonella.
- Avoid contact with calves or lambs at farms or petting zoos: These animals are high risk for various infectious diseases such as Cryptosporidium and Salmonella.
These recommendations also largely apply to other high-risk groups, including people (of all ages) with compromised immune systems and young children (especially less than 5 years of age). A key point is normal contact with common household pest using basic hygiene practices is considered a low risk. Infection control isn't rocket science. It involves basic and practical measures that can reduce risks associated with animal contact.
Parasite exposure from pets
A recent study from the Netherlands investigated the prevalence of zoonotic parasites in pet feces and on pets' haircoats. The authors sampled feces and fur from dogs and cats, and looked for Toxocara (roundworms), Toxoplasma, Giardia and Cryptosporidium. All these parasites are of concern from a public health standpoint because they can be found in healthy pets and can also infect people.
Toxocara eggs were found on the haircoats of 12% of dogs and 3.4% of cats. Levels were low, ranging from 1-31 eggs per sample. An important aspect of this study was that they also assessed viability of these eggs, and found that none were viable. Therefore, even though eggs were present, they were not relevant because they were dead. Exposure to UV light and lack of humiditiy were cited as possible reasons for the death of the eggs.
Toxocara were found in the feces of 4.4% of dogs and 4.6% of cats, which is consistent with other studies of healthy pets.
Toxoplasma was not found in the feces of any cat. (Cats are the hosts for this parasite so dogs weren't tested.)
Giardia was found in the feces of 15% of dogs and 13.6% of cats. However, when these strains were typed, the vast majority were species-specific types that do not cause disease in people. Only 2 of the 15 Giardia samples were assemblage A, a type that is transmissible from pets to people. This is very important to know because crude Giardia numbers don't tell you the whole story.
Cryptosporidium was found in feces of 8.7% of dogs and 4.6% of cats. However, they were not able to type these parasites to determine if they were species that typically cause infection in humans, or whether they were Cryptosporidium felis or C. canis, which rarely cause disease in people.
The discussion section of the paper contains an interesting and relevant point about exposure to Toxocara eggs on the haircoat of pets. The authors state "Even in the worst case scenario of highly contaminated fur, e.g. with the highest Toxocara [eggs per gram] of 300 and an embryonated rate of 4% from the study of Wolfe and Wright, it is necessary to ingest more than 4 grams of hair, with 12 embryonated eggs per gram, to ingest 50 infective eggs." Based on these data, exposure to parasites from the haircoat of pets is quite unlikely. It might be a greater concern with stray or debilitated animals, or with puppies/kittens, who could have much greater coat contamination.
The take home message: Normal contact with healthy pets likely poses minimal risk of transmission of zoonotic parasites. That being said, regularly washing your hands is still a good idea because of the potential for exposure to other types of microorganisms (e.g. bacteria), and in rare circumstances where there may be large parasite burdens on a pet. Good deworming practices, particularly for puppies and kittens, also need to be considered.
Reference: Overgaauw et al, Veterinary Parasitology, 2009.
Water Foul - Cryptosporidiosis
- Cryptosporidium hominis primarily infects humans. Clearly it can make people sick, whether their immune systems are weakened or not.
- Cryptosporidium parvum primarily infects calves, and clearly makes people (and calves) sick. However, because it is relatively common in people as well, in many cases it is hard to say if a person with C. parvum was infected by contact with calf stool or human sewage.
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Both the dog-associated C. canis and cat-associated C. felis have been found in people, and C. felis can cause diarrhea even in immunocompetent individuals. Infection with these species in humans is very uncommon compared to C. hominis and C. parvum- The largest outbreak of cryptosporidiosis ever reported in North America occurred in Milwaukee in 1993, when an estimated 1.6 million people were exposed to the parasite and over 400 000 people became sick as a result of the infection.
- In most studies, contact with pets is either not associated with the risk of cryptosporidiosis or may even have a slight protective effect. One study showed no significant association between pet ownership and cryptosporidiosis in HIV patients.
