Diseases People Catch From Their Pets
Zoonotic Illnesses Of Dogs Cats And Other Pets

Ron Hines DVM PhD 5/4/06

We derive a lot of joy and solace from our pets. They are our non-judgmental companions that give unqualified love. However, on occasion, they give us germs and parasites that make us ill. Diseases passed from animals to man are called zoonoses or zoonotic illnesses. Because of good hygiene and veterinary care, animal-transmitted diseases are rarer in the United States than they once were. The following is a list of some of the diseases pets and livestock pass on to human beings. They are ones that come to my mind as I write this article. It is not meant to be all-inclusive. I do not want you to read this article and become fearful of owning animals. All the conditions I discuss are quite rare. Living life to the fullest has its risks but a little caution on your part is all that is required.

WORMS THAT LIVE IN YOUR PET:

Hookworms and roundworms
Hookworms and roundworms (Ancylostoma and Ascaris ) are common nematodes of dogs and cats. When a human accidentally eats something contaminated with worm eggs from a pet’s stool, the eggs hatch in the intestines and begin migrating throughout that person’s body. Worm larva can also burrow through intact skin. Because these parasites were designed to live in dogs and cats, they become lost in the human body – often in the liver or eyes. When this occurs, the disease is called visceral larval migrans. This disease occurs most often in children due to their poor hygienic practices. In the eye the larval nematodes cause inflammation and blindness. In the liver they can cause chills, fever, malaise and an elevated white blood cell count. To prevent this disease, have your pet’s stool checked yearly for parasites and feed a monthly heartworm preventative that also kills nematodes. Both popular brands of heartworm preventative for dogs contain ingredients that keep your pet free of intestinal worms. Pyrantel pamoate is a very effective medicine to remove hook and roundworms. It is sold on the pet isle at WalMart.

The eggs of the roundworm of raccoons, Balisascaris, are particularly dangerous when ingested by people. If you keep pet raccoons or raise orphans, worm them frequently with pyrantel pamoate and milbemycin oxime. If you have neighborhood raccoons, do not leave dog or cat food outside where it will attract them. Keep your trash cans well covered and seal up attic crawl spaces where these animals can nest.

Tapeworms
Certain tapeworms that encyst in the muscles of livestock and fish can also infect humans. Taenia solium is carried through pork, T. saginata by beef and Diphyllobothrium latum by fish. The common pigmy tapeworm of dogs and cats (dipylidium) that I see frequently in dogs and cats is never infectious to people. Besides the three tapeworms previously mentioned, Echinococcus granulosa, can infect people. The first three develop in the human intestine while the last can cause major damage to the human brain and body organs. Praziquantel and fenbendazole destroy these parasites.

Dog Heartworms
On rare occasions, dog heartworms will infect human beings. This parasite, Dirofilaria immitus, is spread dog to dog by mosquitoes. When a mosquito obtains a blood meal from an infected dog and then goes on to bite the owner it is common for some of the heartworm larva to be transferred to the human. In a normal person, the body’s immune system quickly recognizes the parasite and destroys it. In rare instances, however, the larval heartworm manages to migrate to the person’s lungs where the dying parasite stimulates an inflammatory lesion called a “coin lesion”. These lesions are not serious in themselves but they become very significant when they are misinterpreted as being lung tumors. This is not a very common occurrence for example, within the last twenty years in the United States about eighty cases were reported in the State of Florida.

PROTOZOAN DISEASES:
Protozoa are microscopic single-celled organisms. The vast majority of protozoa live free in the environment or as harmless inhabitants of the body but some are capable of causing disease.

Giardia
Giardia lamblia is a small motile protozoan that inhabits the intestines of mammals and birds. There are many strains of giardia and it is unclear how many are infectious to people. Giardia is the most common form of non-bacterial diarrhea in people in the United States. Children are most commonly affected. Many cases are silent with no overt symptoms. When diarrhea does occur, the illness normally lasts one or two weeks but chronic cases in frail people have lasted for years. Outbreaks due to contaminated water supply occur from time to time in humans. Metronidazole (Flagyl) is an effective treatment in animals and man.

Cryptosporidium
Cryptosporidium parvum causes diarrhea in dogs, cats, rodents, young calves and people. It is found throughout the World. It is passed from individual to individual through fecal contamination. The disease in animals and man is usually mild and self-limiting. Signs of the disease include diarrhea, abdominal pain and flu-like symptoms that can last up to six weeks. The disease is more severe in very old and very young animals and people. In immunocompromized individuals it may cause chronic inflammation of the digestive tract. The disease is passed through fecal contamination from animals or man. The organism is quite resistant to drying and disinfectants so, it can survive a long time in contaminated waste. Signs in people and animals besides loose watery diarrhea include stomach cramps and mild fever. In healthy people, symptoms last about two weeks.

Toxoplasmosis
Toxoplasmosis is caused by Toxoplasma gondii, a small single-celled protozoan. About forty percent of the people in the United States have been exposed to the disease at some point in their lives. The complete life cycle of toxoplasmosis occurs only in cats. These felines become infected by preying on infected birds and rodents. Most cats show no symptoms of disease. In these cats, the organism lives within the cells that line the small intestine. Cats are the only animals that shed this ineffective stage of this protozoan called an oocyst. Most exposures of humans to oocysts cause no overt disease. In a small percentage, however, the oocysts proliferates in many organs of the body causing fever, malaise, enlarged lymph nodes, headache, sore throat and muscle pain. In severe cases the central nervous system, eyes and liver become inflamed. Eating raw or poorly cooked meat of an infected animal is another way this disease is passed on to man. If a
woman becomes infected during the later two thirds of pregnancy toxoplasmosis may cause severe fetal abnormalities. This is why obstetricians suggest pregnant women not change cat litter boxes.

VIRUS:

Viral Encephalitis
Eastern, Western and St. Louis encephalitis are passed to humans through the bite of an infected mosquito. Encephalitis is an inflammation of the brain. Horses also suffer from these diseases but they are dead end hosts that do not pass the infection on. The reservoir animals for these viruses are migratory water birds.

West Nile Virus
West Nile virus generally affects humans birds and horses. The disease causes an inflammation of the brain or encephalitis. It is transmitted from animal to animal and animal to person by the bite of an infected mosquito. In 2002 the disease sickened about 2000 people and resulted in 94 deaths. In horses, the mortality rate is about 30 percent. Dogs are resistant to the disease but cases have occurred in cats, goats, chipmunks rabbits, skunks, bats, llamas and domestic birds.

ORF
The parapoxvirus that causes this disease is found in goats and sheep throughout the United States. In livestock, the virus causes inflammation and scabs on the lips, nostrils, mouth and around the penis or vulva. Transmission to humans occurs thorough infected wool or contaminated sharp objects used on the animals. In people, single lesions develop on the hands, arm or face. These lesions are easily mistaken for abscessed. They heal in six to eight weeks without treatment.

Rabies
The flagship virus that we all associate with wildlife is rabies. Any species of warm-blooded animal is susceptible to this disease but the most common carriers in the United States are bats, foxes, raccoons and skunks. The disease is passed by a saliva-contaminated bite. Occasionally the disease will leave its wildlife reservoirs and infect dogs and cattle. Excellent vaccines exist to protect your pets from this disease. People like me who work with wildlife can, themselves, be immunized against rabies.

B-Virus in Monkeys
Herpesvirus simiae or B-virus is a normal inhabitant of the mouth of macaque monkeys. Approximately 80-90% of adult macaques are infected. Many species of macaques are offered as pets in the United States. This dangerous disease is mild to asymptomatic in monkeys. It causes a lifelong infection with intermittent shedding of the virus in saliva and genital secretions – particularly during periods of stress. Among monkeys it is transmitted sexually and by bites. This virus can cause fatal meningoencephalitis (the veil-like covering of the brain) in people. It is usually transmitted by a bite. In these patients treatment with acyclovir can be life saving. These species of Old World monkeys should never be kept as pets because of the threat of B-virus and tuberculosis (see my article in this series on diseases transmissible from monkeys to man).

Hantavirus of Rodents
Hantavirus pulmonary syndrome is a rare viral disease associated with wild deer mice. It occurs primarily in the fall when rodents move indoors to escape the cold. In the process of the human body attacking the virus in the linings of blood vessels throughout the body, the capillaries are damaged and leak (increased permeability). In humans this causes life-threatening pneumonia, edema, bleeding, fever and kidney failure. Infected mice pass the virus in urine, saliva and feces. Although not a serious disease in rodent the disease in humans is often fatal. People contract the disease by breathing in aerosolized or pulverized virus in rodent urine and feces. Rodent control around the home is the best way to protect against this disease.

BACTERIAL DISEASE:

Salmonellosis
Salmonella are a group of intestinal bacteria that can cause disease in animals and man. In birds and small mammals salmonella causes diarrhea, septicemia (blood infections) and asymptomatic carrier states. People too, like “Typhoid Mary” can carry and spread the disease without signs of disease. Common animal carriers of these bacteria are reptiles, rats and mice. People with a robust immune system rarely experience more than severe cramps and diarrhea. However in infants and people with weak immune systems the disease can be life-threatening.

Shigella
Shigella flexneri is an intestinal bacterium responsible for severe diarrhea in people and non-human primates (monkeys). About 25,000 cases are reported in people in the United States every year. Many monkeys carry this bacteria without symptoms. People are also common carriers. Small children at child care facilities and people who handle monkeys are most at risk. The diarrhea produced in people exposed to human or monkey waste is never life threatening but during the two to three weeks the diarrhea lasts, the victim is quite ill. The chief danger from this disease is dehydration.

Pasteurellosis
Many rabbit farms harbor Pasteurella multocida in their stock. Most rabbits that carry this disease show no symptoms. Some have eye infections and enlarged lymph nodes of the head and neck. A respiratory disease in rabbits, caused by these bacteria is called snuffles. Poultry also develop Pasteurellosis. In birds the disease is called hemorrhagic septicemia. The bacteria is also carried in the mouth of many cats leading to contaminated cat bites. The most common form of Pasteurellosis in people is a skin and soft tissue infection at the site of a bite or scratch. When people’s eyes are exposed to Pasteurella they may develop a severe eye infections. On rare occasions it will cause pneumonia.

Campylobacter
Campylobacteriosis is a bacterial disease caused by Campylobacter jejuni, an organism that lives in the intestinal tract of many animals. The signs of this disease are diarrhea, cramping, abdominal pain and fever. The illness typically lasts one week. It is worse in the very young and the very old. Many infections are silent with no symptoms at all. Most people become infected by handling or eating raw poultry. Occasionally it is spread through contact with the wastes of pet dogs and cats.

Streptococcus and Staphylococci
These bacteria are found on all animals that typically associate with humans. In the great majority of cases they cause no disease in the animal. However, in pets, eye infections are occasionally associated with Streptococci and skin infections with Staphylococci. Both bacteria can spread from pets to humans on contaminated hands and objects. Infections are generally limited to the skin and eyes.

Tuberculosis
Tuberculosis is a chronic infection of the lungs and lymph nodes of many species of animals. Dogs and cats are quite resistant to this disease but cattle, deer and monkeys are quite susceptible. The organism responsible for tuberculosis is Mycobacterium tuberculosis. There are specific strains that affect each type of animal but all of them on occasion infect humans. The human strain is passed from victim to victim by a cough. Before the advent of pasteurization, raw milk was the major source of the bovine strain. Pet African and Asian monkeys are now a common source of exposure. Unfortunately, new strains of tuberculosis are now often immune to the most common anti-tuberculosis drugs, isoniazide and rifampin.

Plague
This infection, caused by a bacteria, Yersinia pestis, occurs naturally in a number of wild rodents including prairie dogs in well defined areas of the southwestern United States. It is transmitted from rodent to rodent and rodent to man through the bite of a flea. Occasionally a domestic cat will obtain the disease from prey rodents and pass it on to their owners. Yersinia was responsible for the scourge of the Middle Ages, bubonic plague.

Parrot Fever, Psittacosis or Ornithosis
Parrot fever or chlamydiosis is caused by a small intracellular bacteria, Chlamydia psittaci, that lives within the respiratory system of birds. A similar organism, which doesn’t seem to affect humans, is found in cats. Transmission is through inhalation of dust, dander and nasal secretions of infected birds – especially parrots and turkeys. The flu-like illness that develops ranges from very mild to life-threatening. In rare instances the heart and liver become involved. The disease is often misdiagnosed as influenza. When a correct diagnosis is made psittacosis responds well to antibiotics of the tetracycline class.

Anthrax
Anthrax, caused by Bacillus anthracis, is primarily a disease of cloven-footed animals. The disease is often fatal to animals and man. This bacteria produces spores or “seeds” that remain infectious for years in the soil under the right conditions. It kills cattle very rapidly – the first sign of the disease being death. It is sometimes confused with lightening strike or snake bite. Prior to death the cows are weak and have difficulty breathing. Their blood may refuse to clot. In humans the lung or pulmonic form of the disease is the most fatal. It is spread through contact with the carcasses of infected animals. It can also occur on the hands and arms as small pus-filled lesions called carbuncles. If caught early the disease is curable with penicillin or tetracycline.

Leptospirosis
There are several species of Leptospira that can transfer from animals to man. The organisms are often associated with rats and swine. In mammals they cause a generalized infection that often localizes in the kidneys. Urine from these animals late in the disease is highly infectious. It is pass through contaminated water. In people, signs of leptospirosis include headache, vomiting, muscle pain and ,occasionally, hepatitis, meningitis and kidney failure.

Brucellosis
When brucellosis occurs in people it is called undulant fever or Malta fever. In cattle it is caused by a bacterium, Brucella abortus. In cattle, deer, elk, swine and goats and dogs different species of the bacteria attack the reproductive organs or cause generalized malaise and fever. In people brucellosis causes long-term malaise, joint pain, intermittent fevers and flu-like signs and fatigue. Brucellosis has almost been eradicated from cattle in the United States.

Helicobacter pylori
This spiral bacteria is capable of forming ulcers in the stomachs of animals and people. It resides in the stomach and the upper area of the small intestine called the duodenum. We suspect that on occasion, it is spread to humans from cats dogs and ferrets through poor sanitation. In dogs, cats and people the most frequent sign of Helicobacter is intermittent vomiting. Affected individuals may also become nauseous, loose their appetite, and lose weight. Amoxicillin, metronidazole and H2 antacids such as famotidine or cimetidine cure the disease in animals and man.

Cat Scratch Fever (Bartonellosis)
This infection, caused by Bartonella henselae, is commonly acquired from asymptomatic (clinically normal) carrier cats. About half of the outdoor cats in the southern United States have been exposed at one time or another to the disease (please read my article on Cat Scratch Fever). We think it is spread by the cat flea. People infected with this disease by a contaminated cat scratch or bite experience fever, malaise and enlarged painful lymph nodes as well as a local inflammation at the site of the wound.

Q Fever
Q fever is a zoonotic disease caused by Coxiella burnetti, a bacteria found world wide. Cattle, sheep and goats are the principle reservoirs of the disease. Most human cases occur in veterinarians, meat plant workers and farmers that raise sheep and cattle. The organisms are excreted in milk, urine and feces. These bacteria are tough, they resist heat, drying and common disinfectants and they live for long periods of time in the environment. They can also be transferred to humans by ticks. Only one half of the people exposed to Coxiella burnetti develop disease. When they do, fevers up to 105F are common along with severe headaches, malaise, muscle aches, sore throat, chills, sweats, cough, nausea, vomiting, diarrhea, abdominal and chest pain and confusion. These symptoms last for 1-2 weeks. During this time some patients develop hepatitis. One or two percent of infected people die of the disease due to secondary heart inflammation (endocarditis) and liver failure.
Doxycycline is the treatment of choice for acute Q fever. Quinolone antibiotics such as ciprofloxacin also work well.

Tularemia Or Rabbit Fever
This disease, caused by Francisella tularensis is associated with rabbits and rodents. It was first formally recognized in 1911 in Tulare County, California in ground squirrels. It occurs in two forms, a glandular form affecting the lymph nodes and a more acute and severe typhoidal form affecting the entire body. In the first instance the organism enters through a scratch. In the second it is inhaled. The disease in man is characterized by high fever, painful, enlarged lymph nodes, chills, myalgia and malaise. On rare occasions it attacks the brain, heart and bones. Ticks are the most common method of spread of the disease from animals to man. When it is passed from direct handling of wild rabbit carcasses inflamed lesions are primarily on the hands. It can also be transmitted in undercooked meat consumed from infected animals.

TICK BORNE DISEASES:
Ticks that feed on wildlife reservoirs of diseases will sometimes transfer them to your pets. If the ticks later leave the pet and bite the owner for their next blood meal they may transfer a number of diseases caused by bacteria, rickettsia and spirochetes.

Lyme Disease
First seen in Lyme, Connecticut, lyme disease is an illness caused by a bacteria, Borrelia burgdorferi. This group of bacteria are called spirochetes due to their spring-like shape. The most common source of infected ticks are household dogs. In humans, this disease causes a wide variety of signs including rash, painful, swollen joints, fever, enlarged tender lymph nodes and a variety of neurological signs (please read the article in this series on Lyme disease in pets and man). Over the last few years a number of products have come onto the market that are quite good at keeping ticks off your pets. Three of these products are Frontline spray, Revolution and Preventic tick collars. Dogs can also be vaccinated to prevent this disease.

Rocky Mountain Spotted Fever
Rocky Mountain spotted fever is the most severe and most common rickettsial illness in the United States. It is caused by Rickettsia rickettsii, a bacteria that is spread to humans by ticks that have fed on infected wildlife. The signs of this disease are fever, headache, muscle pain and spotted rash. The rash is very dark – hence its nickname, Black Measles.

FUNGI:

Ringworm
Ringworm is not a worm and is not always ring-shaped. It is a slow growing fungus that feeds on dead skin cells and hair of all species of mammal. The most common one, Microsporum canis, is common on juvenile cats and dogs where it appears as a dry, oval, scurfy patch of broken off hair. Many of these lesions glow brightly under ultraviolet light. The spores of these fungi often contaminate brushes and cloth that have been in touch with the pet. If these spores come in contact with abraded skin, the fungal infection may transfer to the pet owner.

PRION DISEASE:

Spongiform encephalopathy
These organisms which are more primitive than virus occur naturally in a number of animals. The current large reservoir of prions are cattle that were feed meat and bone meal derived from infected ruminants. When the disease appears in cows it is called Mad Cow Disease or Bovine Spongiform Encephalopathy (BSE). When it occurs in sheep it is called scrapie. In cats it is called feline spongiform encephalitis. Prions are unique pathogens in that they are very slow to cause disease and can not be destroyed by ordinary methods of sanitation. Humans become infected by eating contaminated meat products. When the disease occurs in humans it is called Creutzfeldt-Jakob disease. The signs of this disease in humans mimic Alzheimer’s Disease.

SKIN PARASITES:
Fleas and ticks are parasites that transfer readily from pets to people. Because they do not actually “infect” people or pets I do not discuss them in this article. You can read about them in other articles in this series.

Sarcoptic Mange Or Scabies
Mange mites are common on large and small, wild and domestic animals. Mange mites are not particular as to the species of animal they attack. Dog and cat mange mites are Sarcoptes scabei. Initially they are most common on the ears, face and extremities but with time the entire body becomes affected. These mites are passed from animal to animal by direct contact. They do not survive long off the host. The mites burrow through the deeper layers of the skin causing intense itching and a red rash. From this the term “seven year itch” was derived. They are easily killed with ivermectin, dips or Selamectin (Revolution).

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