Cats, Dogs,


And Other House Pets

     Generally speaking, cats are more likely than dogs to spread disease to children and household members.  Furthermore, cats, more than other pets, spread disease to dogs and other companion animals.  Cats are a threat to humans by their many diseases, including rabies.  Cat’s bites, scratches, or fleas from cats may transmit several kinds of infections.

     One of the most serious and widespread diseases from cats is toxoplasmosis.  The toxoplasma antibodies are common in human blood serum indicating a previous infection with toxoplasma organisms. In adults the symptoms may be mild and resemble “flu.”  A regular occurrence is chorioretinitis (blindness) in children of mothers who were apparently affected during pregnancy.  Toxoplasmosis also causes mental retardation, hydrocephalus, eye diseases, deformities, and other neurological disorders that may not become apparent until after childhood.

     Fetal death in late pregnancy or the newborn period is a frequent result of toxoplasma infection in the mother.  Toxoplasma may also be contracted by eating raw or inadequately cooked meat, and from several kinds of livestock and pets.  It is notable and probably highly significant that Eskimos have no cats and no toxoplasmosis.

     Different from toxoplasma is toxocara, the common roundworm of most dogs and cats.  When humans are infested with these worms, they produce a disease called visceral larva migrans.  The child comes down with very ordinary symptoms of bronchitis, fever, enlarged liver, and some pneumonia.  Many cases are passed off as the flu or a cold.  This makes the true incidence in man nearly impossible to determine.  The eosinophil count in the blood is sometimes high.  (Eosinophils are white blood cells which become more numerous in the blood of persons having allergies and infections with parasites.)  While the disease is generally mild, it tends to hang on for a few months. Occasionally there have been fatalities reported.  The dog or cat hookworm can cause cutaneous larva migrans or creeping eruption, an intensely itchy skin from which patients generally recover without any treatment.  Journal Of Dairy Research

     A two-year-old began to feel bad with a runny nose and fever.  In a very short time, he developed cough and paleness.  He started to lose weight.  He was given a large number of drugs including Dimetapp, ampicillin, theophylline, and dexamethasone.  His white cell count was 19,000 with 44% eosinophils (normal is 0-3).  The family had recently acquired a new puppy and had had a cat for several years.  Roundworm and tapeworm ova were found in the puppy.  A sister who had played with the puppy also had a runny nose which had been diagnosed as “allergic rhinitis.”  The child was tested for Toxocara by the usual tests (indirect hemagglutination and bentonite flocculation titers to Toxocara) and found to be negative.  But when the boys serum was tested for specific antibodies for Toxocara, he was found to have a very high titer, diagnostic for the dog and cat roundworm.  He recovered after a few weeks of illness.  Southern Medical Journal  April, 1980.

     About half of all dogs and cats harbor Pasteurella Multo cida, a germ causing redness, swelling, pain, and bite.  It will eventually develop abscesses and hard red flesh around the bite with enlarged lymph nodes in the nearby areas.  The disease may spread to produce hemorrhagic septicemia (Blood poisoning), osteomyelitis, and meningitis.

     Cat scratch fever can be obtained from a cat or dog scratch, a bite of an animal, or from a rose thorn scratch from roses grown in places where cats play.  In the area of the scratch, there is a blister which leads to an ulcer.  A fever develops and the nearby lymph nodes enlarge and sometimes open up and drain pus.  Patients recover without treatment in a few weeks or months.

     Rheumatoid arthritis patients have been shown to have greater exposure to sick animals than did control patients.  This suggests that pets may serve as a reservoir for infectious agents causing rheumatoid arthritis.


     Psittacosis, a pulmonary disease with fever, shortness of breath, cough and other respiratory tract symptoms can be contracted from birds.  The mortality rate is 5 to 10 percent.  Patients often do not suspect they have caught a disease from birds.  Pet hamsters have been the source of an outbreak of lymphocytic choriomeningitis, a disease characteristically producing a fever, headache, and severe muscle aches.

     Histoplasmosis, a fungus disease causing symptoms that range from insignificant to fatal, can be acquired particularly from exposure to infected flocks in the chicken houses.  Two hundred thousand new cases are expected to occur every year in America.

     Other diseases from animals include vesicular stomatitis, and pox virus.  Herpes virus are found in all animal species, including birds.  Influenza of man and swine flu are biologically related.  The 1918-1919 influenza outbreak in both humans and hogs were simultaneous.  The disease was caused by the combined activity of hemophylus influenza suis and a filterable virus. The disease made its first appearance in autumn of 1918.  The serums of most humans born after 1918 contains antibodies to swine flu: those born before 1918 have no antibodies.  Epidemics began explosively in October or November, and were usually finished by March.  The Hong Kong flu virus, first identified in man in 1968, is antigenically related to an influenza virus first isolated from horses in 1963, and is thought to be the same virus.

     Newborn infants may contract listeriosis, a disease that causes fever during pregnancy, but is usually undiagnosed.  The baby gets the germ during passage through the birth canal or is infected from environmental sources.  Cows, goats, sheep, hogs, poultry (especially turkeys), fish, crabs, and rabbits are known reservoirs of the disease.

     Monkeys are no friends of humans.  They are dangerous pet and can transmit measles, encephalitis (arboviruses), amoebic dysentery, and many other serious illnesses.  Hemorrhagic disease of monkeys begins as a severe case of feeling bad followed by impaired consciousness, headache, high fever, vomiting, diarrhea, and a rash on the skin and inside the mouth.  The eyes become red and sore and the lymph nodes become swollen.  There is bleeding into many tissues and body openings with signs of involvement of both the central and peripheral nerves.  About one-third of the cases die!  Monkeys can also transmit tuberculosis and hepatitis.  Fifty documented cases of hepatitis are mentioned in a single report.   Pediatrics, October, 1965.

     It has been suggested that systemic lupus erythematosus is a disease of animals transmitted to man.  However, a test on eleven dogs of patients who had systemic lupus failed to support the hypothesis that lupus is a disease of animals.  Nevertheless, the implication is not banished by the results of this one report. Further studies on the relationship of lupus to animal disease are urgently needed.

     Non-human reservoirs for human cholera exist in cows, goats, dogs, and chickens.  These reservoirs in animals may serve as sources of infection in humans.   Journal Of Infectious Disease, December 1974


     A large number of diseases are transmitted from wild animals.  Dogs were once the principal source of human rabies, but during the past two decades, wild animals such as the bat, skunk, fox and raccoon have been the principal sources.  In recent years, fewer than five cases of human rabies have been reported in the United States per year.

     The bobcat has been discovered to be the carrier in a case of human plague.  Eighteen cases of human plague occurred in the United States in 1980.  Monthly Morbidity And Mortality  Report, April 3, 1981.  A 25-year-old rancher began having headaches, chills, and fever progressing to vomiting and a massive swelling in the left armpit.  He had cut his left hand shortly before skinning a bobcat.  The patient died a few days later.

     Rocky Mountain spotted fever is thought to be primarily an infection of wild rodents spread to man by several species of ticks.  This includes both wood and dog ticks.

     The reservoir for the protozoan Giardia lamblia, which is a common cause of diarrhea, weight loss, and intestinal malabsoption, is now felt to be both wild and domesticated animals.  The beaver has been definitely implicated, and dogs and other animals are suspected.


     Imported bone meal is the only material to which the general public is exposed that is potentially infected with anthrax.  Infected bone meal is incorporated in the feed of animals, and bone meal is sometimes used as fertilizer in agriculture.  Journal Of Hygiene, September, 1972.

     It is difficult to know how many infections are exchanged between man and his animal domestics.  Recent figures indicates that 130 to 150 major and 80 to 90 minor diseases are shared by man and animals.  Years ago, Ralph Nader said that at least 30 diseases were considered transmissible to man through meat, milk, poultry, eggs, and other foods of animal origin.

     From the material presented in this chapter it can be readily discerned that there is no safety in owning domesticated animals, and that animal products are a hazard in the diets of humans.

A. & C. Thrash