Zoonosis: (zo”o-no’ sëz) a disease of animals that may be transmitted to man. (Dorland’s Medical Dictionary)
Pet ownership is associated with improved immune function, lowered blood pressure, and better survival following heart attack, stroke, or cancer.
However, it is not without some risk.
The following is a brief description of some illnesses occasionally seen in Indiana. Several of the diseases cause more significant illness in children, or in individuals with weakened immune systems.
Visceral larval migrans (migration of immature worms through the soft tissues of the body) is associated with exposure to the eggs of ROUNDWORMS, most commonly Toxocara cati or Toxocara canis (Baylisascaris procyonis, the raccoon roundworm has been isolated from dogs, and is the most dangerous and aggressive roundworm parasite). Symptoms relate to the organ(s) affected by the migration, i.e.: coughing (lungs); upset stomach (stomach, small intestines, liver); blindness (retina of eye - especially with Baylisascaris); paralysis, coma, mental changes, (brain - usually Baylisascaris).
Cutaneous larval migrans, a skin rash, usually after laying or playing is wet grass, is caused by hookworm larva (Ancylostoma or Uncinariaspp.). These larva hatch out one to three days after being deposited in stool, and swim in the drops of dew on plants until they can grab a passing animal and burrow into the skin. They are frequently confused with “Chiggers”, (a bird mite). In rare cases, the Northern Hookworm will migrate to the intestinal tract and create a form of chronic Inflammatory Bowel Disease in people.
Control of these parasites is by prompt removal of waste from the environment (most roundworm eggs must lay in the environment for one to three weeks before becoming infectious — an exception is Baylisascaris, which are immediately infectious— and as stated previously, hookworm eggs require 1 to 3 days). Routine deworming of all puppies, and routine parasite checks of all adults followed by appropriate deworming is also important. Other control methods include keeping children’s sandboxes covered when not in use, and enforcing thorough hand washing WITH SOAP before eating or drinking after playing in public parks. Since raccoon roundworms are infectious when they leave the hosts body, and also are the most likely to migrate to nerve or eye tissue (therefore, causing the most serious damage), carefully monitoring children playing outside, discouraging raccoons from residing in the neighborhood, and watching for signs of raccoon latrine areas in order to keep children (and pets) away, is important.
Dipylidium caninum, the “flea” tapeworm, occasionally has been associated with infections in children following ingestion of the intermediate host (fleas, roaches, other bugs). Control is by controlling fleas and other pest insect reservoirs.
Another tapeworm: Echinococcus, is associated with deer, antelope, and cattle as the intermediate host. This tape worm affects canids (dogs, wolves, coyote, fox) as the primary host. This tapeworm causes a VERY SERIOUS condition referred to as Hydatid Disease in people exposed to the infectious eggs in dog stool. Control of dog stool, controlling free roaming dogs, and preventing dogs from eating raw meat, especially deer or beef, is very important. Again, routine deworming with appropriate deworming medication is helpful.
Dirofilaia immitis (canine heartworm), occasionally causes “coin” lesions on human X-RAYS (may be confused with malignant cancer metastasis), but has not been associated with illness in people. Exposure is “shared source” with dogs, that is, getting bitten by mosquitoes, not from dogs themselves.
Protozoal parasites of include Cryptosporidium, Giardia, Isospora, Entamoebaand Toxoplasmosis, . In healthy individuals, these parasites may be associated with a brief flu like episode, however, they may become life threatening in very young or immunocompramized individuals. First time Toxoplasmosis infections in pregnant women (first trimester) may result in brain or eye disease in the developing baby. Toxomplasma eggs require two to three days in the environment before becoming infectious, so direct contact with cats is unlikely to be a risk factor.
To avoid infection, individuals at risk should:
1) not feed undercooked or raw meat, or allow pets to hunt (avoid exposure to the parasites)
2) always clean the cat’s litterbox daily, flush or incinerate the feces, clean the box with scalding water, scoop the yard at least once daily of dog waste.
3) wear gloves when working with soil (I.e.: gardening)
4) always keep the children’s sandbox covered
5) always boil water that is obtained in the environment for drinking (when camping out, etc.)
6) control other potential carrier hosts such as earthworms, and cockroaches
7) always cook meats to at least medium well
8) observe proper hygiene and wear latex gloves when handling raw meat (including field dressing)
Toxoplasmosis may be shed by cats with positive or negative blood titers. Cats recently infected with Toxoplasmosis shed the most eggs, and for the longest period of time – usually fourteen days – but test negative, while cats which are chronically infected usually only shed following major stress, and then in low numbers, but will test positive on blood tests. There is no known treatment to remove Toxoplasmosis from the cats body, but the antibiotic Clindamycin has been shown to reduce shedding. Women who have been exposed to Toxoplasmosis before becoming pregnant are not at risk of infecting their unborn baby.
bacterial & rickettsial diseases:
intestinal: Salmonella, Campylobacter, E.coli, Yersinia enterocolitica and Shigella can affect pets and may cause symptoms in people exposed to their feces. Salmonella infections in dogs are usually subclinical (no signs). Salmonella frequently affects pets which hunt and eat wild birds (song-bird fever).
Helicobacter pylori has been isolated from one colony of cats, this agent causes stomach ulcers in people. Salmonella infections in cats may be subclinical (no symptoms), or cause abortion or intestinal signs (diarrhea/vomiting). This bacteria is usually associated with cats that prey on wildlife, especially birds (song-bird fever). Prevention includes:
1) proper sanitation and hand washing
2) preventing hunting and predatory behavior.
bites and exhudate exposure: Francisella tularensis (tularemia – rabbit fever) causes abscess formation, septicemia and general illness in cats exposed to wild rodents or rabbits. Most bacterial infections associated with bite or scratch wounds lead only to local infections in people. Immunocompromised individuals exposed to Pasteurella or Capnocytophaga (DF-2) may develop serious clinical illness including fever, weakness, and malaise, in rare cases death may occur. Appropriate medical attention, including antibiotics, is generally effective. Due to the variety and potency of bacteria in the mouths of cats, current guidelines from the Centers for Disease Control recommend all cat bite wounds be promptly treated by a physician.
Bartonella spp. have recently been identified as the cause of “Cat Scratch Disease”. Illness develops approximately three weeks after exposure, and may include lymph node swelling, fever, weight loss, headache, eye irritation, skin eruptions, and joint pain. Most cases are self limiting, but may take several months to clear up. Cats may be infected by fleas. The disease is more likely to be passed by kittens then by adult cats. Coxiella burnetii, (Q fever) is a disease of cats, dogs, cows and people usually transmitted by ticks. Cats usually show no signs of illness while people develop fever, weakness, headache, pneumonia, liver enlargement, and sometimes heart disease. People have been exposed by air born contact from a queen giving birth or aborting.
respiratory diseases: Chlamydia psittaci commonly causes mild eye disease in cats. This agent can also cause conjunctivitis (pink-eye) in people following direct contact with eye discharges of infected cats, antibiotic ointments are generally effective.
reproductive and urinary disease: Brucella canis and Leptospira spp. may infect dogs and be transmitted to people by contact with urine or reproductive discharges. Borrelia burgdorferi (Lyme disease) is not generally present in high enough concentration to infect people, people are usually infected from "shared vector" exposure (tick bites).
Rocky Mountain Spotted Fever and Q Fever (Rickettsia rickettsii and Coxiella burnetii) usually infect people from shared vectors (ticks, etc.) but may be present in urine , milk, blood, or, with Q fever, may be air borne.
viral disease: Rabies is the only significant viral zoonosis in the United States, it may be carried by any species of mammal, however, it is most commonly associated with raccoons, skunks, and bats. Dogs may be infected with Venezuelan Equine Encephalitis virus (VEE) by infected mosquitoes and people become infected from the same source. Feline Immunodeficiency Virus (Feline AIDs) and Feline Leukemia Virus are species specific to cats only. West Nile Virus has been associated with scattered infections in dogs and cats, and is generally a fatal infection in horses and birds. People may become infected by West Nile Virus from mosquito bites (shared vector).
fungal disease: Many systemic fungal infections affect both pets and people. Usually, as in Histoplasmosis infections, theses are shared source infections (not from animal to man or vice versa, but both exposed to the same environmental source). However, Blastomyces dermatitidis has been transmitted to humans by bites from infected dogs. Sporothrix schenckii (rose growers disease) has also been transmitted by direct animal contact. Sporothrix is found in the soil throughout the world, cats with wounds infected with this agent may produce large numbers of organisms in exudates, symptoms in people are generally the same as in pets, (draining wounds). Special antifungal drugs are needed to treat this infections. Keeping pets indoors helps avoid their exposure to the agent. Dermatophytes (ring worm fungus: Microsporium & Trichophyton spp.) commonly infect pets with or without showing symptoms. The characteristic rash readily responds to appropriate antifungal ointments or oral medications, but may require weeks or months of treatment to clear. Special diagnostic tests are available to detect pets that carry the fungus without showing symptoms. Kittens, especially kittens from shelters, are the most commonly infected.
arthropod diseases: Sarcoptic mange — scabies (Sarcoptes scabiei) may infect people from infected dogs. The cat flea (the most common flea found in the United States also will feed on humans for a brief period of time if dogs or cats are not readily available. There is no evidence that the human head louse is able to infect pets. Lice may however live on pets for a short period of time (1 to 10 days) just as they may live on clothing, bedding, etc. Most commercial flea products will also kill lice.
management of pets for immunodeficient people:
Adult pets that live entirely indoors and have healthy teeth and gums are not likely to be at risk of carrying disease.
If acquiring a new pet, adopting an adult cat that has been living strictly indoors in a private home is safest. Otherwise, the pet may be quarantined from the immunodeficient individual while it is screened for ringworm, Giardia, Cryptosporidium, Bartonella, and at the same time, dewormed for roundworms and hookworms.
If a dog is chosen, adult dogs that are walked outdoors on leash in controlled environments are at low risk of picking up illness. A non-immunocompramized individual should be responsible for cleaning up stool and brushing the pets teeth. No pets should not be allowed to lick an immune suppressed individual on the face or be present at meal time.
Zoonosis of other pet species:
Reptiles, amphibians, fish, birds, ferrets, and other “exotic” pets each have their own unique set of infectious diseases and risks. Currently, none of these pets can be recommended for anyone that has a weakened immune system.