Animal Writes
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5 March 2000 Issue
Zoonoses, An Animal-Rights Issue?

by [email protected]

Animal welfare means protecting animals from people, animal control means protecting the people from the animals. If we can assuage public concern about diseases that can be transmitted to people by domestic and wild animals, we may be able to foster tolerance for all animals.

As incredible as it seems in this day and age, we all know of someone who still believes that cats shouldn't be around babies because they “suck the breath out of the baby”; or that pregnant women must surrender their housecats to shelters to avoid toxoplasmosis. Not all stray dogs are rabid, not all rodents carry disease, and not all cat scratches lead to cat-scratch fever.

By far, it is not contact with wild animals but with our own pets that produce the most incidences of zoonotic disease transmission. The most common route of zoonoses is bite wounds. Statistics show that 4.7 million people are bitten by dogs every year in the United States. Of these, approximately 800,000 people require medical intervention. That is, each year 1.8% of the U.S. population is bitten by a dog, and 0.3% of the U.S. population seeks medical care for a bite (Centers for Disease Control).

Bite wounds can lead to serious bacterial infections because of the oral bacteria in a pets’ mouth. Cat Scratch Fever is caused by a bacteria called Bartonella Henselea found in cat saliva and on cat claws. Intestinal worms of pets are also transmissible to people. Roundworms and hookworms are passed in the feces of infected animals. If ingested by humans, the worms can migrate through the body (visceral larval migrans). They generally migrate to the eye, leading to blindness. Toxoplasmosis is a single-celled protozoan. It is of particular consideration to immunosuppressed people and pregnant women. The prevailing source of toxoplasmosis in people is from eating undercooked meat, but it is considered a zoonotic disease because a cat can contract toxoplasmosis from eating infected raw meat, and pass it on in their feces. It can then be transmitted to people who clean their litter boxes, or children who play in areas where infected cats have defecated. The simple way to avoid toxoplasmosis is to wear rubber gloves when cleaning a litter box, or have another family member do it.

Another prevalent source of zoonotic infections is pet’s skin. Ringworm (which is a fungus, not a worm) can be passed from pets to people and from people to pets. Zoonotic diseases and the risk of bite wounds can be reduced by early puppy/kitten socialization, commonsense hygiene and annual visits to a vet for parasite checks and vaccinations.

Medical professionals working in human hospitals frequently get prophylactic vaccinations such as hepatitis, influenza, and tetanus and are routinely tested for tuberculosis. However, animal-care workers, with the possible exception of pre-exposure rabies vaccines, do not normally get vaccinated against zoonotic diseases. Yet, surprisingly, the incidence of zoonoses is relatively small. Veterinarians, and others whose jobs bring them in close working contact with animals, have no higher degree of the illnesses of diseases that also occur in animals than the general population does.

When an alarming number of persons are diagnosed with the same disease within a short period of time, an epidemic is declared. Epizootic is the word we use when the same thing happens to animals. Because the threat to human life is so viable, there are several laws in place, which are meant to protect the general public from diseases that can be passed from animals to humans. Some of these laws cross state lines. Most state laws require diligent reporting of instances of animal-related diseases in humans. Some of the diseases or conditions are declared so dangerous as to be a threat to the public health. Treating physicians and veterinarians, as well as the caregivers of people and animals who have been found, upon their death, to have had this disease, are required by law to report the event within 48 hours of the finding. The list of zoonotic diseases includes 52 major diseases, but not all of them are subject to government regulations regarding reporting of confirmed diagnoses of these diseases. Some of the diseases of which some states require due notification are:

Animal bite by potentially rabid animal

Encephalitis* Anthrax

Food or waterborne diseases Botulism

Hepatitis Giardiasis

Meningitis Hookworm*

Meningococcal Disease Pertussus

Rubella Malaria

Salmonellosis* Rabies

Shigellosis Tetanus

Syphilis Typhus

Tuberculosis Histoplasmosis

* (only if found in human subject)

In order to keep zoonotic diseases in check, vaccines have been developed to protect not only domesticated house pets and their owners, but zoo animals and cattle as well. These vaccines not only protect the animals, but the animal-care workers who are in close proximity to large numbers of animals. Most of the vaccines that are offered and used extensively are done so on a voluntary basis. The rabies vaccine, however, is a mandatory vaccine in the United States.

Rabies is a highly contagious, deadly zoonotic disease. It’s a common misconception that only dogs and raccoons can get rabies. The truth is any mammal can get rabies. The most common carriers of rabies are skunks, bats, coyotes and foxes. However, there are documented cases of rabid horses and cows as well.

If any disease has fed into the hysteria surrounding diseases that can affect both human and non-human animals alike, it’s rabies. Known medically as hydrophobia, rabies is a serious virus infection of the central nervous system, transmitted by the bite of infected animals. So a certain amount of education is necessary to avoid any unfortunate end results of this hysteria: the unnecessary and unwarranted killing of animals who intrude on human territory simply because they “may have rabies”. A collective, deeper understanding of rabies and how it is identified and transmitted may go a long way toward saving the lives of animals who are not infected with the rabies virus but are at risk for being killed anyway. The two most common of these classes of animals are domestic pets that bite; and wild animals that appear in and around populated communities.

Rabies occurs rarely in the United States, but there is still public fear and substantial prevention efforts continue. The reason for this very serious effort at prevention is that rabies is always a deadly disease for both humans and non-human animals. There is no cure for rabies. The vast majority of rabies cases reported to the Centers for Disease Control and Prevention (CDC) each year occur in wild animals like raccoons, skunks, bats, and foxes. Domestic animals account for less than 10% of the reported rabies cases, with cats, cattle, and dogs most often reported rabid.

There are two forms of rabies: Furious rabies largely affects the brain and causes an infected animal to be aggressive or excitable (the very picture of the foaming-at-the-mouth, "mad dog" image people have of rabies). Paralytic or "dumb" rabies, mainly affects the spinal cord, causing the animal to be weak-limbed, lethargic, and unable to raise its head or make sounds because neck and throat muscles are paralyzed. In the beginning phase of paralytic rabies, an animal may also appear to be choking (USDA).

In the case of transmission by wild animals, it is important to note that very few of the wild animals that wander into a person’s backyard is rabid. Wildlife experts agree that people should not encourage wild animals into their yard by feeding them or leaving garbage cans in such a way as to entice wild animals such as raccoons and foxes. Most wildlife rehabilitators believe that wild animals should be left alone. If they are creating a nuisance, the most humane way to rid a property of unwanted feral animals is to wait until they leave their nest (usually at night), and then render the space uninhabitable by placing a blockage of some sort over the access point. Of course, you can’t do this if the home is serving as a nest for infant animals.

The bottom line is that there are a lot of diseases, some still being discovered, that are easily transmissible from animals to humans. There are many more that are not so easily transmitted. Education on the part of the public will go a long way toward keeping safe from zoonotic diseases and saving wildlife that are sometimes killed for no reason other than “they carry disease”. Complying with local regulations for domestic animal vaccinations, and becoming more educated and tolerant of wild animals is the key to keeping rabies and other zoonotic diseases in check, and living in harmony with other species.

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