Zoonotic diseases (zoonosis) are infections that can be passed from animals to humans. Zoonotic diseases are more common in those who have pets, handle animals as part of their occupation, and live in proximity of wild animals, farms or in areas where biting of humans by animals is known.
Precautions against zoonotic diseases include taking care while handling animals and their products through proper protective gear, coverings and clothing, and making sure that the water and food being consumed are not contaminated. Proper refrigeration of animal products and cooking them well before eating, pasteurization of milk, and ensuring clean drinking water, are important points to protect against zoonotic diseases.
Though laboratory tests are available to test the blood of the infected patient for each of these diseases to reach a confirmed diagnosis, very often treatment is initiated immediately based on the area or region and environment where the patient lives or works, history of bite or possibility of exposure to a particular animal or its meat, and the presenting symptoms.
Here is an overview of some well-known zoonotic diseases:
RABIES
Rabies is a viral disease transmitted by infected animals through their saliva, by biting or scratching humans, or lhe licking human wounds, eyes, nose, and mouth. Dogs are the most common cause of rabies, but other animals like cats, monkeys/raccoons, bats, horses, cattle, goats, and fox, can also transmit the virus.
Rabies presents with burning, irritation, tingling, pain, or numbness at the bite wound, along with fever, sore-throat, cough, fatigue, body ache, and nausea-vomiting-diarrhea, followed later by aggression, confusion, seizures, paralysis and hydrophobia (painful spasms in the throat when a person tries to drink water).
If there is any suspicion of exposure to rabies, one should seek immediate medical attention as the disease can be fatal. Treatment is called post-exposure prophylaxis (PEP) which includes wound care, human rabies immune globulin (HRIG), and a dosage series of the rabies vaccine. To prevent rabies in the community, vaccinating all dogs is the most effective way.
ANTHRAX
Anthrax is a rare but serious bacterial disease that is caused by the bacteria Bacillus anthracis, spread through contact with infected animals or contaminated animal products. Anthrax is found naturally in soil and its spores can survive in the environment for decades. It commonly affects livestock and wild animals. It can be transmitted through the skin, lungs, or gastrointestinal tract. Anthrax is not known to spread from person to person, but it can be transmitted in rare cases of close contact with an infected person.
- Cutaneous anthrax: The most common form of anthrax in humans. It’s caused by skin contact with contaminated animal products like wool, hair, bone, or hide. The bacteria enter through a cut or scrape in the skin. Injection anthrax is a newly recognized form of anthrax associated with intravenous drug use.
- Inhalation anthrax: Caused by breathing in anthrax spores from contaminated hides or wool. It’s the most severe form of anthrax.
- Gastrointestinal anthrax: Caused by eating contaminated or undercooked meat from infected animals., or drinking water contaminated with spores. It
Anthrax presents as flu-like symptoms: Sore throat, mild fever, fatigue, muscle aches, nausea, coughing up blood, and painful swallowing, shortness of breath, high fever, and trouble breathing. Skin anthrax presents with an itchy sore that may be swollen, blister, and turn into a black ulcer.
Treatment is with hospitalization and early commencement of antibiotics. Options include Fluoroquinolone class (like ciprofloxacin, levofloxacin), penicillin/amoxicillin, minocycline, doxycycline and tetracycline. Monoclonal antibodies and immunoglobulins to neutralize anthrax toxins may be required. Vaccinating livestock in areas where anthrax has occurred in the past, the proper disposing of dead animals, and avoiding using sick or recently dead animals for food or products, are important preventive measures in the community.
BRUCELLOSIS
Brucellosis is a bacterial infection that is caused by a family of bacteria called Brucella, and spreads through contact with livestock and wild animals like cattle, goats, sheep, wild pigs, bison, etc from their body parts/fluids and contaminated products, like raw milk or undercooked meat, as well as by inhaling airborne bacteria. It’s also known as contagious abortion, Bang’s disease, Malta fever, and undulant fever.
It presents with fever, headache, abdominal pain, loss of appetite, weight loss, joint pain, especially in the hips, knees, or lower back and large, painful lymph nodes. Brucellosis is usually treated with antibiotics (options include streptomycin, gentamicin, doxycycline, ciprofloxacin or rifampicin) for at least 6 weeks. It is important to avoid eating raw or undercooked meat from infected animals, or consuming unpasteurized milk or other dairy products, and to avoid direct contact with infected animals.
PSITTACOSIS
It is also known as parrot fever or ornithosis, and is a bacterial infection caused by the bacteria Chlamydia psittaci. It spread to humans from infected birds by inhaling dust from dried bird droppings, handling infected birds and inhaling bacteria from shed feathers, secretions, and droppings. People who work with birds, such as bird fanciers, poultry workers, and pet shop employees.
It primarily affects the lungs and presents with fever, chills, headache, muscle ache, soreness and swelling in tthe hroat with cough, and shortness of breath. Psittacosis can be treated with antibiotics, mainly doxycycline or tetracycline, and others like erythromycin, azithromycin, ciprofloxacin, chloramphenicol, and rifampicin. Severe cases may require hospital-based ventilation and monitoring. Complications include heart inflammation (myocarditis, pericarditis), encephalopathy, hepatitis, arthritis, and sepsis which can be fatal if not treated timely. Hygienic and safety precautions should be taken while handling and cleaning birds and cages.
TULAREMIA
Tularemia is a rare, potentially life-threatening zoonotic disease, caused by the bacteria Francisella tularensis that can affect both humans and animals. It’s also known as rabbit fever. It spreads through bites from infected ticks and deer flies, skin contact with blood or tissues of infected animals, drinking contaminated water or eating undercooked meat, inhaling contaminated dust or aerosols, and laboratory exposure. People who are in close contact with infected animals or ticks are at risk of tularemia like farmers, veterinarians, hunters, lab workers, meat handlers
It presents with fever, skin ulcers, enlarged lymph nodes, sore throat and dry cough, abdominal pain, nausea-vomiting, diarrhea, and breathlessness. It is treated with antibiotics (options include mainly doxycycline or tetracycline, and others like streptomycin, gentamycin, ciprofloxacin, chloramphenicol, and linezolid). Preventive measures include avoiding contact with infected animals or insects, wearing protective clothes and washing hands after touching animals or insects, the access to clean non-contaminated water and food, cooking meat properly and using insect repellents.
TOXOPLASMOSIS
Toxoplasmosis is caused by the parasite Toxoplasma gondii. It is contracted through exposure to cat stools, ingesting oocysts (cells containing the infective parasites) by drinking contaminated milk/water or eating undercooked meat or raw seafood. It can be prevented by cooking meat thoroughly after freezing it for at least 3 days, and washing fruits, vegetables and one’s hands thoroughly while handling food.
It presents with general symptoms like fever, body ache, headache, sore throat and swollen glands. While it is usually harmless, it can cause serious problems for those who are pregnant or immunocompromised, by affecting multiple organs like the lung (causing breathlessness), brain (causing dizziness, blackouts, seizures), eyes (visual disturbances) and compromising heart and liver function.
Toxoplasmosis is treated with a combination of drugs, usually including pyrimethamine, sulfa antibiotics (or clindamycin if sensitive to sulfa) and folinic acid. The treatment depends on the severity of the infection, the patient’s immune system, and where the infection is located. Treatment is mainly needed for the high-risk groups of pregnant women, infants (who may need long-term treatment for 1-2 years), and the immunocompromised. If visual symptoms are present, an eye-specialist should be immediately consulted. Regular monitoring and follow-up are important as drugs may have adverse effects.
TOXOCARIASIS
Toxoplasmosis should not be confused with Toxocariasis, another of the zoonotic diseases, that can present with similar history and symptoms but has to be treated differently. Toxocariasis is a disease caused by the larvae of the dog or cat roundworm. People become infected by accidentally swallowing eggs in dog/cat stools from contaminated soil, water or food.
Sometimes there may be no symptoms or vague ones like fever, cough, abdominal pain, or headache, and sometimes eye involvement (redness, pain, blurred vision, or squinting) and skin rash. Treatment includes the antiparasitic drugs albendazole or mebendazole. If visual symptoms are present, an eye-specialist should be immediately consulted.
CAT SCRATCH DISEASE
Cat scratch disease is one of the mild zoonotic diseases caused by the bacteria Bartonella henselae. It’s usually a mild illness that resolves on its own within a month. It is contracted by the scratching or biting by an infected cat or kitten, exposure to cat fleas or contact with cat saliva on broken skin or mucosal surfaces. The area of the bite or scratch should be washed with soap and water immediately to prevent infection.
Cat scratch disease presents as a small lump or pustule at the site of a cat scratch or bite, and swollen lymph nodes in the area of the scratch, along with mild fever, fatigue, sore throat, body ache, loss of appetite and sometimes a rash. It’s usually a mild illness that resolves on its own within a month. Local heat application and analgesics on the wound can also help. Antibiotics can treat serious cases or cases in people with weakened immune systems. In rare cases, cat scratch disease can lead to serious neurologic or cardiac complications especially, in those who are immunocompromised.
LYME’S DISEASE
Lyme disease is caused by the bacteria Borrelia burgdorferi, and spreads by ticks found in pets and wild animals. It presents with a rash that is circular like a bull’s-eye, (called erythema migrans), and usually appears within the first 4 weeks after a tick bite. Other symptoms include fever, chills, headache, muscle and joint pain, palpitations, fatigue and sometimes numbness or weakness of hands and feet, and pain starting in the back and hips spreading to the legs. Swollen lymph nodes may also appear.
Lyme disease is treated with antibiotics, usually doxycycline or amoxicillin. Prevention is timely removal and management of ticks in pet animals, and covering arms, hands, legs and feet well while gardening, hiking, camping, fishing, or hunting in tick-infested areas like tall grass, brush, shrubs, or wooded areas.
PLAGUE
Plague is a bacterial disease that can affect humans and other mammals. It is caused by the bacteria Yersinia pestis. Bubonic plague is caused by the bite of an infected rat (rodent) flea by direct contact with rats. Pneumonic plague can be caused by inhaling droplets from an infected person’s cough or sneeze, or by the spread of bacteria from bubonic plague to the lungs. Septicaemic plague is the spread through the blood to multiple organs. Plague has caused epidemics in many countries in the past. Working outdoors or camping, hunting, or hiking in areas where plague-carrying animals reside, increases risk greatly.
It presents with fever, chills, headache, weakness, fatigue, body ache, nausea-vomiting-diarrhea, swollen painful lymph nodes (buboes), and abdominal pain. When infection spreads to the lungs there can be bleeding from the nose, mouth, or under the skin, shortness of breath, chest pain, and cough (with bloody or watery mucus).
Treatment is with antibiotics and should be started within 24 hours on clinical suspicion of exposure, as once the first symptoms occur, the risk for death increases. Antibiotic options include Fluoroquinolone class (like ciprofloxacin, levofloxacin, moxifloxacin), gentamicin, streptomycin, doxycycline and tetracycline. Treatment duration is usually 10–14 days.
Other zoonotic diseases include monkeypox, flu transmitted by birds and pigs, leptospirosis and listeriosis, Q fever (flu-like illness caused by the bacteria Coxiella burnetii) and some viruses like Ebola and Hantan.
Mad cow disease, also known as bovine spongiform encephalopathy (BSE), is a fatal brain disease that affects cattle, causing abnormal nervous or violent behavior, incoordination, and difficulty in walking (making the cow appear mad). Once a cow shows symptoms, it usually dies within two weeks to six months. Rarely eating infected cattle products, including beef, can cause humans to develop a variant of this disease called Creutzfeldt-Jakob disease (vCJD).
Also read:
Water and Food Borne Diseases, and Gastrointestinal Infections
Common Cold and Flu- Know the difference, effective care and 10 alert signs