What Is a Zoonotic Disease?
Most people encounter animals regularly in their daily lives. Some of the ways humans rely on animals are for food, work, sports, and companionship. Unfortunately, sharing lives also means sharing germs and illness. According to the World Health Organization (WHO), a zoonosis or zoonotic disease is any disease or infection that is naturally transmissible from vertebrate animals to humans or from humans to vertebrate animals.
Zoonotic diseases are caused by viruses, bacteria, parasites, protozoa, fungi, and other pathogens. These germs cause a wide variety of illnesses, ranging from mild to serious, and can even cause death. It is important to remember that even if an animal does not appear sick, they can still carry diseases that make humans sick.
How Do Zoonotic Diseases Spread?
Zoonoses can be spread directly in bodily secretions or indirectly from areas where animals live or objects and surfaces they touch. Zoonotic disease can also be transmitted to humans by blood-feeding ticks, mosquitoes, or fleas, and it can be foodborne or waterborne.
Although anyone, even healthy people, can get sick from a zoonotic disease, children under age 5, adults over 65, those who are immunocompromised, and pregnant women are at a higher risk.
Prevention includes being aware of what diseases are common in your area, along with practicing proper hand-washing, preventing bites, practicing food safety, and avoiding scratches from animals.
Diseases From Cat Scratches
Most feline infectious diseases only affect cats, but some can be transmitted from cats to people. The likelihood of people contracting diseases from cat scratches is low, but it is possible, especially in vulnerable populations.
The main concern with cat scratches is transmission of a bacterium called Bartonella henselae, which causes cat-scratch disease (CSD), or cat-scratch fever, and is carried in the saliva of infected cats.
About 40% of cats carry the B. henselae bacterium at some point in their lives, and most cats show no signs of illness. CSD is transmitted to people by cat scratches that break the skin, cat bites that cause wounds, or when infected cats lick open wounds in people.
Other less common health conditions resulting from a cat scratch include ringworm, and some bacterial infections can be zoonotic between cats and people. Ringworm is typically spread by touch, not scratch, from cat to human.
Cat Scratch Disease In Humans
Symptoms of Cat-Scratch Fever in Humans
Clinical signs of cat-scratch fever that you may notice include:
Swelling, blister, or raised lesion with redness or pus where scratched
Sore muscles and joints
Swollen, enlarged, tender, or painful lymph node where scratched
Rarely, those who are immunocompromised, particularly children, may have more serious complications including infections of the bones (osteomyelitis), eyes (neuroretinitis and Parinaud syndrome), brain (encephalopathy), and heart (myocarditis).
Treatment of Cat-Scratch Fever in Humans
Treatment for CSD varies with a person’s age, overall health, symptoms, and how sick the person feels. Antibiotics usually are not needed for CSD lesions, unless the wound appears infected. CSD symptoms are treated by pain medication and by giving fluids for fever and poor appetite. If lymph nodes are swollen and painful, a warm compress may be applied.
If a cat scratch or bite becomes red or swollen and you develop flu-like symptoms, including headache, decreased appetite, fatigue, joint pain, fever, or swollen and painful lymph nodes, contact your healthcare provider as soon as possible.
Most cases of CSD dissipate without medical intervention. Those with rare complications may require intensive antibiotic treatment with azithromycin.
How To Protect Yourself From Diseases From Cat Scratches
To prevent CSD in humans, avoid cat scratches and bites by not playing roughly with them, wash hands after contact, control fleas, and keep cats indoors.
Because most cases of CSD result from contact with kittens that are under 1 year old, those who are immunocompromised should avoid contact. If you are scratched or bitten, wash the area right away with antibacterial soap and water. It is very important to not allow cats to lick any wounds you may have.
Contact your doctor if you suspect your cat may be sick and has scratched you. There are currently no vaccines available for cats against Bartonella.
Long-Term Effects of Cat-Scratch Fever in Humans
Healthy adults generally recover from CSD with no lasting effects, although it may take several months for the skin disease to completely go away.
Those who are immunocompromised may take longer to recover and may require hospitalization and lifelong medical management. In case of rare complications, consult an infectious disease specialist doctor.
US Centers for Disease Control and Prevention. Zoonotic Diseases.
Rahman T, et al. “Zoonotic Diseases: Etiology, Impact, and Control,” Microorganisms, 2020; 8(9): 1405.
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