Plague. Fever, chills, swelling in the armpit and groin area, large dark spots on the skin: These are symptoms of a disease that was once so dreadful its very name has become synonymous with anything that causes serious illness or trouble Plague, or Black Death, killed many thousands of people during epidemics that date back to ancient times. What was the cause of such destruction of human lives? A common flea. You normally think of a flea as being a pest found on cats and dogs. But it was the flea that, through its bite, spread plague from an infected rate to a human.
Plague is only one of the several diseases classified as zoonoses – diseases that can be transferred between animals and humans. Some forms of zoonoses in humans are caused by direct contact with an animal, while other forms are caused by indirect contact with an animal through agents such as the flea, the fly, or the tick.
Like plague, Lyme disease and Rocky Mountain spotted fever are spread to humans indirectly from an animal through the bite of a tick that attaches itself to a person during out-door activity.
Sometimes no bigger than the period at the end of this sentence, the tick that transmits Lyme disease usually lives on white-tailed deer, field mice, and other wild animals whose bodies contain bacteria. The tick, containing the animal’s blood, bites a human, and the bacteria enter the human’s body. A rash often appears at the site of the bite and expands to form a large lesion with a clear area in the center. Other symptoms include fever, chills, headache, stiff neck, and extreme fatigue. If not treated, Lyme disease can affect the central nervous system and cause skin complications and symptoms of arthritis.
Rocky Mountain spotted fever, transmitted primarily by the American dog tick, causes symptoms similar to those of Lyme disease – headache, fever, and skin rash. Also, as with Lyme disease, early diagnosis and treatment with antibiotics prevent more serious complications.
To lessen the chance of tick-borne disease, it’s wise to take precautions when you’re outdoors in parks, fields, or woods. Wear long-sleeved shirts and long pants. Use insect repellent. Check your skin thoroughly when you come indoors. Use flea and tick sprays on your pets, and check them regularly for ticks. If a tick attaches itself to your skin, use tweezers to gently remove it. Clean the area well before and after removal. If a rash later appears, see your physician.
Hunters – Beware
Another disease associated with outdoor activity is tularemia, or rabbit fever. This disease spreads from infected animals, usually wild rabbits, to humans by the direct contact with the animal or through the bite of ticks and flies. Symptoms of the disease include a sudden onset of fever, headache, chills, and vomiting. Later symptoms may include appearance of skin ulcers, inflammation of the eyes, and swelling of the lymph glands. The antibiotic streptomycin is often used to treat tularemia.
Since the disease is transmitted primarily by direct contact with the tissue of an infected animal, hunters should wear rubber gloves when cleaning game, and all game should be thoroughly cooked.
Caution to Pet Owners
These forms of zoonoses are associated with the outdoors, but much closer to home – even in your own living room – danger may lurk. What harm could your striped tabby possibly present? Common household pets can transmit diseases directly to humans unless preventive measures are taken. Cats, for example, transmit cat scratch disease, sometimes called cat scratch fever, to humans. Cat scratch disease (CSD) can affect people who frequently handle cats – especially children who cuddle and play with them. A cat’s saliva carries the bacteria that cause the disease. Humans can catch the disease from a cat’s bite or scratch. Even a lick from a cat to a cut on a human skin is enough to pass along the bacteria. Although this bacteria has been cultured in the laboratory, it remains unidentified. It is thought to be part of the normal bacteria that live in a cat’s mouth, which are transferred to the claws during grooming.
CSD is relatively uncommon, and every scratch from a cat does not lead to the disease. However, if a cat scratch heals slowly and a person’s lymph nodes swell and become tender, a physician should be seen. (Any cat bite can become infected and would require a visit to a physician.) Although CSD may cause discomfort, it rarely is serious. A few preventive measures go a long way. Handle cats gently. If you have a cut or scratch, keep it bandaged while handling cats – and always wash your hands afterwards. You might consider having house cats declawed.
A more serious disease transmitted by cats is toxoplasmosis, caused by a parasite in the cat’s digestive system. It spreads to humans through cat feces or dirt contaminated with cat feces. Cats themselves become infected by killing and eating small rodents.
Toxoplasmosis has a wide range of symptoms including fever, fatigue, swollen lymph glands, cough, sore throat, loss of appetite, and skin rash. Pregnant women are at highest risk of severe consequences of toxoplasmosis. The disease can cause miscarriage or congenital disabilities in the unborn child.
Most people do not develop symptoms of toxoplasmosis because they have antibodies to the disease in their blood. But it is wise to wear protective gloves when cleaning your cat’s litter box, which should be cleaned often, always washing your hands afterwards; also, wash your hands after gardening.
Wildlife and Rabies
Just as cats can transmit forms of zoonoses through direct contact, so can dogs. Worldwide, most cases of rabies occur as a result of dog bites. But where canine rabies has been controlled by immunization, wildlife or cats may still be infected. Rabies, although rare in humans, is deadly. The disease is caused by a virus carried in the saliva of an infected animal. It is transferred to humans most often by a bite, but direct contact with an infected animal’s saliva to broken skin also can result in the disease.
An animal that contracts rabies usually behaves in an unusual way. Wild animals suddenly show no fear of humans. Pets may appear to be anxious, excitable, and aggressive, and they may have unexplained paralysis.
The incubation period for humans that have come in contact with the rabies virus can be as short as nine days or as long as two years. Symptoms in humans include pain or irritation at the site of the virus entry, hyperactivity, anxiety, increased salivation, muscle spasms, convulsions, and coma. Death usually occurs within eight days of the appearance of symptoms if medical treatment is not sought. If you are bitten by a rabid animal, a thorough cleaning of the wound may help prevent the virus from entering the body. But only a series of shots given by a physician can counteract the virus.
The risk of getting rabies drops greatly when preventive measures are taken. If you have pets, make sure you keep their rabies vaccinations up-to-date, and don’t let them roam loose outdoors. And never approach a strange dog or any wild animal.
Prevent Zoonoses with Precaution
There are approximately 100 known zoonoses, but the list constantly changes as new diseases, previously mistaken for more common, exclusively human diseases, are identified. Most zoonoses are relatively rare and can be treated once a diagnosis is made. And many zoonoses can be prevented by using your own good sense.