11 diseases that can pass from animals to humans

Though anthrax is most commonly associated with bioterrorism, this rare disease is actually caused by the bacteria Bacillus anthracis and can be spread by both domestic and wild animals. People can become infected by anthrax if they breathe in anthrax spores, consume contaminated food or water, or are exposed through broken skin.

Symptoms can vary based on the way someone was exposed but often include blisters or sores with a black center, fever, headache, nausea, body pain, shortness of breath, confusion, and painful swallowing. Treatment normally involves taking antibiotics, antitoxin, or both. Anthrax is a serious condition that can be fatal.

According to the World Health Organization, cattle, sheep, goats, antelope, and deer are the most common source of animal-transmitted anthrax. People who work with animals or animal products are most at risk of exposure, though contracting anthrax is still extremely rare.

The orf virus generally affects small ruminants like sheep and goats, but it can be passed to humans through contact with infected animals or contaminated items.

"Orf typically presents with a pustule that ultimately progresses into a sore, usually on the hand. There was an increase in orf diagnoses as goat yoga became popular, but it can occur after visiting a farm or petting zoo as well," board-certified dermatologist Dr. Susan Bard told INSIDER.

You can catch orf from petting infected animals, though the virus can also spread through bites or equipment. The resulting sores can be painful but usually heal on their own in about six weeks as long as they are kept clean, dry, and free of bacterial infection. Orf can't be passed between humans.

Though orf normally isn't dangerous, some more serious zoonotic diseases can sometimes look like orf, including anthrax. It's important to get checked out by a doctor if you suspect you've contracted an infection from a sheep or goat.

Giardia is an intestinal parasite that lives in the infected feces of animals or humans. It can be spread through contact with anything that has been exposed to the infected waste, including water, ice, soil, and household items.

"A pet can track giardia through your home after it's infected. If your pet has symptoms of diarrhea, a rumbly tummy or vomiting you need to see your veterinarian to confirm a diagnosis," veterinarian Dr. Jim D. Carlson told INSIDER.

In humans, giardia can cause diarrhea, gas, greasy stools that float, nausea, and stomach pain. Children and pregnant women infected with giardia are especially prone to severe dehydration. Symptoms generally last between two and six weeks and can start up to three weeks after infection. The infection is generally treated with prescription drugs.

Dr. Carlson advised that floors, furniture, toys, and bedding should all be thoroughly cleaned after contact with an infected pet. It's also important to retest your pet following treatment for giardia to make sure the infection has been fully cleared.

Toxoplasmosis is sometimes confused with Bartonella, but though these conditions are both spread by cats, they're caused by different organisms. Toxoplasmosis is caused by the parasite Toxoplasma gondii and can be caught by contact with infected cat feces or urine. The parasite can't pass through intact skin, so infection usually occurs through the mouth or an open wound.

"The disease is generally quite mild, but can be serious in individuals who are pregnant, going through chemotherapy, or have a compromised immune system. Symptoms can include fatigue, muscle aches, headaches, and fever that can last over a month," infectious disease specialist Dr. Nidhi Ghildayal told INSIDER.

In otherwise healthy people, most cases clear up without treatment within a few months. However, severe cases of toxoplasmosis can cause damage to the brain, eyes, or other organs. The disease can also reactivate years after the initial infection.

To guard against toxoplasmosis, Dr. Carlson told INSIDER that cat owners should keep litter boxes clean and always use gloves and cleaning agents when handling cat feces. Soil can also become infected, so wear gloves if you're gardening in an area frequented by cats.

Fish tank granuloma is a rare skin infection that usually afflicts people who have close contact with fish, according to the American Osteopathic College of Dermatology.

"Fish tank granuloma caused by mycobarium marinum. It usually presents as a red swollen lesion on the skin of those handling tropical fish or cleaning out the tank," said Dr. Bard.

Pet shop staff, aquarium workers, or people who work with raw shellfish are especially at risk, though anyone who comes into contact with tropical fish or their tanks can catch it. The most common infection site is the back of the dominant hand, where painful sores can develop. Fish tank granuloma is treated with extended courses of antibiotics, though it can take up to two years to completely heal.

To prevent contracting fish tank granuloma, wear waterproof gloves when handling fish and raw shellfish or cleaning fish tanks and limit your exposure to non-chlorinated standing water.

Psittacosis, also known as parrot fever, is an infection caused by the bacteria Chlamydia psittaci.

"Psittacosis can be spread when individuals inhale respiratory fluids or feces from parrots, pigeons, macaws, parakeets, and other birds that carry the bacterial infection. Birds may not show symptoms, so the disease can be hard to detect," said Dr. Ghildayal

Psittacosis can cause fever, headache, and a dry cough in humans. Though the infection is rarely serious and can usually be easily treated with antibiotics, it can lead to pneumonia in some people.

Keep bird cages as clean as possible, avoid bird overcrowding, and make sure feces and other waste can't pass between cages to help prevent Psittacosis. You should also wear gloves and masks when handling infected birds and cages.

Dr. Bard told INSIDER that one of the most common zoonotic skin infections is ringworm. Despite its name, ringworm is actually a fungal infection and is usually contracted from cats, dogs, and other pets. It causes a distinctive circular rash that is usually itchy and red.

"Zoonotic strains of ringworm tend to be more inflammatory than other strains. It is easily treated with topical or oral antifungals," said Dr. Bard.

Ringworm can live on household items like bedding, furniture, and clothing. Though you can get it from animals, the fungus can also be spread from person to person. Wear gloves when touching items that have come into contact with a ringworm-infected person or pet and always wash your hands after handling animals.

Salmonella is most commonly associated with contaminated food, but Dr. Fiorito told INSIDER that you can actually contract a Salmonella infection through contact with reptiles like lizards, snakes, and turtles or amphibians such as frogs or salamanders.

"A Salmonella outbreak tied to bearded dragons spread to 31 states from 2012 to 2014. It was a rare strain that was antibiotic-resistant. The majority of those sickened were five years and younger, but fortunately, there were no deaths," said Dr. Fiorito.

Symptoms of Salmonella in healthy adults are usually limited to diarrhea, abdominal cramps, fever, and vomiting and normally resolve without treatment. However, people with compromised immune systems such as children and the elderly can become seriously or fatally ill. Talk to your healthcare provider if you suspect you have a Salmonella infection.

Leptospirosis, or Weil's disease, is a bacterial infection that typically affects farmers and those who work directly with livestock like pigs, sheep, and cattle.

"Leptospirosis is typically transmitted through direct contact with infected animal urine. Symptoms are normally mild and flu-like. More severe infections can lead to yellowing of eyes or the skin, or liver and kidney failure," Dr. Adeline Peters, general practitioner and lead physician at DoctorOnCall, told INSIDER.

Horses, dogs, and rodents can also carry the infection, which is often passed to humans through contaminated water, contact with broken skin, or the mucous membranes in the eyes, nose, or mouth. With antibiotic treatment, people normally heal in three weeks to a month. Without treatment, recovery may take months.

One of the most notorious zoonotic diseases is rabies, a virus that is almost always lethal.

"This disease infects the central nervous symptom and results in death if not medically treated with urgency. Rabies is often spread through the saliva of an infected raccoon, coyote, bat, skunk, fox, dog, or cat — in fact, any mammal can spread the disease," explained Dr. Ghildayal.

Early symptoms of rabies include headache, weakness, and a prickling or itching at the infection site, according to the WHO. As the infection progresses, fever, confusion, agitation, and seizures may develop. People with advanced rabies may also exhibit hydrophobia, or fear of water.

Unfortunately, rabies is almost always fatal once symptoms develop. The CDC reported that there have only ever been 10 documented cases of recovery from rabies, and only two of those people survived without immediate treatment.

"Travelers need to be wary in foreign countries about petting local animals, such as stray dogs. A person can get rabies without being bitten, such as when the saliva of the animal infiltrates cuts on the neck or face," warned Dr. Fiorito.

It's extremely important that anyone who may have possibly been exposed to rabies gets treated as soon as possible. Treatment usually consists of four vaccines administered over 30 days. According to the NHS, post-exposure treatment is nearly 100% effective if received immediately after exposure.