Grades: 10-12

Zoonotic diseases are diseases that are transmissible between animals and humans.

What does the term zoonosis mean?

"A disease of animals transmissible to man." People can contract some animal diseases, but not all of them. You should be aware of how these diseases are transmitted, their symptoms in both people and animals, and how to prevent them.

Start by downloading the lesson handouts (pdf) and printing them out. They include fun games, puzzles, and quizzes to help your child learn.

What animals are involved in transmission of zoonotic disease?

All animals can be involved in one or several different diseases, from insects to mammals and birds to fish. These animals can play a variety of roles. Some are involved in direct transmission and act as the host (cats and Toxoplasma gondii), or the vector (ticks and Lyme Disease). The cat (host) is infected with T. gondii. The tick (vector) carries the bacteria that causes Lyme Disease. Some animals act as a carrier of the disease or reservoir, allowing the disease to remain in the population but unable to transmit the infection directly. They can also be called intermediate hosts (mice and Toxoplasma gondii). The animals that are infected with these diseases may or may not show clinical signs, therefore testing and preventative medicine are very important methods of control.

Why are zoonotic diseases important?

These diseases can cause a variety of different diseases which can make people very sick, and in some cases even cause death (rabies). They are especially important for people with immune compromising illnesses. A disease that may make a healthy person feel under the weather for a few days can be life threatening for persons with diseases such as HIV/AIDS, cancer and undergoing chemotherapy, liver or kidney disease. This does not mean that these people should not own pets or be around animals, just that they should be very vigilant about cleanliness and preventative health care for their pets.

How are zoonotic diseases transmitted? Who are the culprits?

Parasites, protozoa, and ectoparasites.

Parasites:

"Parasitism is a way of living in which an organism, the parasite, uses an organism of a different species, the host, both as habitat and food."

In the majority of parasitic zoonotic diseases, the transmission from animal to human is via an oral-fecal route. This means from feces to mouth. This is common with endoparasites. Many of you will say, “I would never eat dog or cat feces so how does this concern me?” Transmission, however, is much more subtle than you might think.

Have you ever thought about the cat that uses a vegetable garden for a toilet? How about the toddler that is playing and falling in the grass of a public area where dogs defecate?

• Toxacara canis or roundworms: These worms can be found in puppies as young as 21 days of age and become infective in the outside environment 1 to 2 weeks after they were shed by the animal (host). Dogs may have a bloated stomach and not gain weight as would be expected. In humans, the larvae can migrate to the eyes and cause blindness in severe cases (Visceral Larval Migrans).
• Ancylostimum caninum, A. braziliense or hookworms: These worms are found in dogs, cats and other carnivores. They can be seen in puppies as early as 21 days. Puppies may appear weak and generally not doing well. In humans the larvae migrate through the skin causing intense itching (Cutaneous Larval Migrans).
• Dipylidiasis or tapeworms: This is extremely common in dogs and is also seen in cats. Humans become infected through ingestion of the intermediate host, the flea, and usually show no signs. Dogs and cats may have rice like particles in the fur around their anus, which are the egg packets and are diagnostic but not infective. This is another reason that flea protection is very important.

None of these diseases are common in North America because of good preventive measures such as these:

• Yearly examinations for dogs and cats. Examination of feces for the eggs of these heliminths and regular de-worming.
• Poop and Scoop laws
• Flea Control
• Good hygiene, washing hands after handling animals or soil, and before eating.

Protozoa:

"Protozoa are singular cell organisms that are also transmitted by an oral -fecal mode."

• Toxoplasma gondii: The host is the cat. The cat contracts this parasite from eating mice and other raw meat. After infection, the cat excretes eggs (oocytes) in the feces for one to two weeks and the eggs become infective in two or three days. The cat does not show any symptoms and there are rarely any clinical signs in adults unless they are immunocompromised. Human infection occurs from oral-fecal route (I.e. unwashed vegetables from the garden), eating raw meat and from mother to child in the uterus. But DON'T SHOOT THE CAT! At least 40% of the population in North America has already been exposed to this parasite. Pregnant women are only at risk if they have not been previously exposed. By taking some simple precautions such as having someone else clean the litter box daily (eggs take 2-3 days to become infective), keeping your cat indoors, not feeding them raw meat, thoroughly cleaning and cooking your food and washing your hands, this should not be a problem and is no reason to get rid of the cat.
• Giardia and Cryptosporidia: These are protozoa that can cause diarrhea which is generally not life threatening unless the person is immunocompromised. People most commonly contract this by drinking or eating food that has been washed with water contaminated with infected animal or human feces. Has anyone ever heard about Traveler's Diarrhea? When traveling in areas such as Central and South America, you should never drink untreated water.

Ectoparasites:

These are multicellular organisms: fleas, ticks, mites, flies, and mosquitos.

These parasites carry and transmit a number of bacterial and rickettsial diseases, acting as vectors. Transmission of disease by ectoparasites is usually through the blood. An ectoparasite bites an animal, becomes infected and transmits the disease to humans.

When the ectoparasite bites an infected animal (reservoir) it takes the disease causing agent into it's body during the blood meal. In general, the infective agent must then develop in the body of this insect (intermediate host), or be passed on to it's offspring, before it can be transmitted to humans. Some of diseases that are transmitted by Ectoparasites are:

• Rocky Mountain Spotted Fever: A rickettsial disease, transmitted by ticks with dogs as the reservoir. It is found in the western and southeastern US, not in Canada. Ticks generally become infected by feeding on rabbits and rodents. Ticks can only transmit disease after feeding on the host for 5 to 20 hours so early discovery and prompt removal of ticks reduces the chance of infection.
• Lyme Disease: This is a bacterial disease which is transmitted by the deer tick and can affect both dogs and people. It is called Lyme Disease because it was first reported in Lyme, Connecticut in 1975. It is transmitted by saliva from the tick during a blood meal. It can cause arthritis in dogs. Humans develop a rash after being bitten by ticks and can also develop arthritis and heart disease. This is not prevalent in Canada, but the ticks that carry this disease have been found in New Brunswick.

How do you think these diseases can be controlled?

Controlling the vectors, flea control, insecticidal sprays that are safe for use on pets, daily checking for ticks if you live in, or visit an infested area, prompt removal of ticks, avoid infected areas and wear long protective clothing. Identify any dogs that may be infected and seek immediate treatment. Also, try to prevent your dog from roaming in high grass and in unknown areas.

Bacterial, Rickettsial and Mycotic Infections

This group of diseases can be contracted by direct contact with an infected source. These organisms can enter through the nose, eyes, mouth, or through cuts on the body. The organisms are carried in a variety of body fluids including saliva, fluids from the reproductive tract and aborted fetuses, and feces.

Some of these zoonotic diseases include:

• Salmonellosis: This is a bacterial disease which can be found in the feces of a number of species of animals. It is common in exotic pets such as turtles and reptiles. Often these animals will appear clinically healthy. This is most serious for immunocompromised people, however, most cases are not associated with pet exposure. In humans, this bacteria can cause diarrhea.
• Cat Scratch Disease: This is caused by a small gram negative bacteria (Bartonella) and can be transmitted by cat scratches or bites. This condition appears as a small pustule, which can lead to regional involvement of the lymph nodes.
• Dermatomycosis or Ringworm: This is a fungal infection that affects the skin of both animals and humans. It is transmitted by direct contact between an infected individual and another animal or human. It is often difficult to say if the animal gave the ringworm to the person or vice versa. In animals there is usually hair loss on the affected areas and crusty looking skin. Humans usually have a red raised area that may be itchy. Both animals and humans can be treated effectively with antifungal medications and this is not a reason to get rid of the animal!

How can these types of zoonotic diseases be prevented?

Identify affected animals and seek treatment. Practice good hygiene. Always wash your hand before eating, after handling animals, and if you have a cut or scrape. Avoid rough handling cats because this may lead to scratches or bites. Do not allow animals to lick open wounds or cuts. Wear protective clothing if you know an animal is infected with a zoonotic disease, and if you are handling bodily fluids, i.e. gloves or a mask.

Bites

Animal bites can be a serious occurrence with respect to physical trauma and potential for infection. Many bites go unreported but they still account for 1% of emergency room visits in the U.S. There are a number of bacteria which live in the mouths of dogs and cats and can cause serious infections. Cats have long sharp teeth which literally puncture the skin and inject bacteria (Pasturella multocida) under the surface. Because of the shape of the wound, the skin often closes quickly and the bacteria are trapped inside. Bacteria can travel rapidly in the blood stream and cause serious illness, even death if not treated. The best prevention is to treat animals kindly and with respect to prevent bites. If a bite does occur, seek immediate medical attention for you and/or your pet.

Rabies

Rabies is a viral disease in which is transmitted from the saliva of an affected animal into the blood stream of another animal or human. This can occur via a bite or by aerosol droplets of saliva onto mucous membranes (mouth, eyes). Human rabies is rare in North America because we practice effective vaccination of our domestic dogs and cats.

However, for those humans who contract this disease and do not receive immediate treatment, the disease is 100% fatal. Humans who are bitten should receive immediate prophylactic treatment. Prevention is through ensuring that your animals have current rabies vaccinations, avoiding animals that are unfamiliar or wild animals that are acting strange. Rabies can take up to 6 months to reach an infective state but once the animal begins to show signs, such as excessive salivation, change in behavior or aggression and un-coordination, death will soon follow. Animals that bite should be quarantined for a certain period of time depending on their vaccination status, to monitor for signs of infection. If the animal displays symptoms, he/she should be euthanized. The animal's brain is sent for testing at an approved federal laboratory.

Conclusion

Zoonotic diseases are a scary reality, but there are things that we can do to protect ourselves from them. For our animals, vaccinations are the first line of defense against disease, also, keep an eye on where you animal goes, and what they come in contact with. For humans, be sure to always wash your hands after handling animals, and before eating or drinking. Also, be aware of animals around that may bite or scratch you. If you have any questions, please feel free to contact our office.