Dogs, cats and small mammals such as rabbits or guinea pigs are popular companions for many people, often sharing their home environment. Being in such close contact, it is perhaps inevitable that sometimes disease is transmitted from pets to their owners. Though the diseases discussed in this article can affect any person, immunocompromised people such as infants, the elderly or those who are HIV+ need to be extra careful. This article looks at skin diseases of dogs and cats that can present a risk to their owners.

Actually, considering the large number of people interacting closely with small animals on a daily basis, the overall risk of contracting disease from a pet with skin disease is remarkably low. In general, keeping pets clean, free from parasites and healthy, as well as good personal and household hygiene such as proper hand washing, will minimize the risk of catching a disease from your pet. However, people belonging to risk categories (the immunosuppressed) need more specific advice.

The increase in pet travel, and the occurrence of breeders sourcing stock from overseas, has made the risk of exposure to new diseases a little greater. The most common skin diseases transmissible to humans that occur in dogs and cats are sarcoptic mange (scabies), cheyletiellosis (mite infestation), fleas and dermatophytosis (ringworm). In general, young and newly acquired animals, especially those from animal shelters, are most likely to be affected by these diseases. Below we look at each of these diseases more closely.

Flea Infestation

Since the reservoir of fleas is predominantly in the environment, and jump onto the human from there, one might argue that this is not strictly transmitted from the animal. However, it is introduced into the household by the animal and therefore falls into this category.

The flea will readily feed on humans and can cause a marked hypersensitivity reaction in some individuals. In addition, fleas can transmit other diseases, such as cat scratch disease (Bartonella henselae), tapeworm (Dipylidium caninum) and plague (Yersinia pestis). Regular flea control with veterinary recommended spot on treatments will keep the environmental population of fleas low, and minimize the risk of bites.

Sarcoptic Mange

This is caused by the mite Sarcoptes scabiei, and can affect a number of species. Different strains of the mite do tend to prefer different species, and the most common one which affects dogs and foxes only has an estimated 20 per cent chance of transmission to humans. Prolonged skin to skin contact is the main route of transmission, with the disease presenting as an itchy rash with small red spots. Usually, disease in the human will clear up of its own accord, once the dog has been treated appropriately with a medicated shampoo or spot on drug. Occasionally, humans may need their own treatment though. It is very important to treat all in contact dogs as well. Unlike fleas, these mites do not tend to survive for long in the environment so reinfection is rare once the dog has been treated.

Cheyletiellosis

This can be caught from dogs, cats and small mammals such as rabbits or guinea pigs. Mites can survive in the environment for several days. Humans are only transiently infected, and develop itchy spots. Appropriate treatment of the affected animal, and the in contact animals, resolves the problem.

Dermatophytosis (Ringworm)

This is actually a type of fungus, not a worm as the name suggests. The most common type in dogs and cats is Microsporum canis. Transmission is often by direct contact, but spores can remain infective in the environment for many months. Dogs and cats may be carriers of the disease without showing any signs of it themselves, while acting as a source of infection for their owners.

In dogs and cats, infections with ringworm usually resolve by themselves given time, unless the animal is immunocompromised (e.g. on steroids). However, treatment is recommended so that the risk of transmission to humans is lessened. Dogs and cats are usually treated with a topical solution of itraconazole, while affected humans are usually prescribed an anti fungal cream to apply to affected areas.

Otodectic Mange (Ear Mites)

These mites cause ear infections in dogs, cats and ferrets. They can, rarely, affect skin outside of the ear, and this has been reported sometimes in humans. It is however rare, and easily controlled by treating the affected animal with a certain acaricidal spot on drug (e.g. selamectin, moxidectin) or topical ear drops.

Malassezia Dermatitis

These are yeasts often found on normal skin in dogs, cats, humans and other species. Skin disease occurs as a reaction to the yeasts overgrowth and the hosts reaction to it. Transmission to humans has only ever been documented in immunocompromised people, and the risk of infection is low.

Staphylococcal Infections

Staphylococcal pyoderma (bacterial skin infection) is common in dogs, but not in cats. It often occurs secondary to another disease and usually involves the bacterium Staphylococcus intermedius. Contrast this to humans, where the main cause of bacterial skin infection is Staphylococcus aureus, and it is clear that the risk of transmission to humans is very low.

Mycobacterial Infections

Tuberculosis poses a risk to human health. The bacteria Mycobacterium tuberculosis and Mycobacterium bovis can infect both cats and humans, and pass between them. The disease presents as nodules, draining tracts or non healing wounds, or as respiratory disease. Urgent medical and veterinary attention should be sought, though the incidence of pets passing it to their owners is very low.

Feline Poxvirus Infection

Cats get cowpox infections by being bitten by voles and wood mice. Hence it is only outdoor cats that are affected, namely those that hunt. Many affected cats do not show any signs of disease. Transmission to humans is rare, and can cause painful skin nodules.

What can immunocompromised people do to minimize the risk to them?

Firstly, a risk assessment should be carried out. Good communication is essential between the medical and veterinary professionals involved. The goal is to maintain disease free status in the pet, whilst practicing thorough hygiene measures by the person. Being immunocompromised does not mean you cannot have a pet, but the following points should be taken into consideration:

1. If acquiring a pet, make sure it is a healthy one, vet checked and not from a source rife with diseases.
2. Safe feeding practices
3. Avoid your pet coming into contact with contaminated material from other animals (e.g. feces)
4. Vaccination annually
5. Good worming control (every 3 months in adult dogs and cats)
6. Good flea prevention (usually monthly for spot ons)
7. Good dental care (brushing your pets teeth, dental chews to keep teeth clean)
8. Regular general health checks by your veterinarian