Top 20 animal-borne diseases (zoonoses)

Diseases don’t just spread between humans. Animals can also transmit different pathogens to us.

When we fall ill we tend to think that it was because another person has passed their germs to us. This is true in many cases, although we generally tend to overlook the fact that perhaps the person who has infected us has not been another human being, but an animal.

In fact, 6 out of 10 times we get sick it is because an animal has transmitted some pathogen to us. This is more than half, and taking into account that applying prevention measures in animals is much more complicated than in people, the problem of the transmission of pathogens through animals is a public health problem worldwide.

What is a zoonosis?

A zoonosis is any disease of a specific animal that is accidentally infected to a human being, where the pathogen begins to develop and cause damage.

Animals can transmit all kinds of pathogens, including bacteria, viruses and fungi . One of the main problems is that the animals may seem perfectly healthy, but if they come into contact with a human, these germs can cause an infection.

The variety of zoonotic diseases is very wide, since their characteristics depend both on the animal that transmits them and on the pathogen in question. The conditions they cause can be mild, moderate, or severe, and even lead to the person’s death.

How does the pathogen pass from animal to human?

There are different ways that can allow the pathogen to jump from the animal to the human and cause a disease. These forms of contagion are classified as follows.

Direct contact

The person comes into contact with fluids from the animal that contain the pathogen, such as saliva, urine, blood, feces, mucous membranes…

It is especially dangerous when it comes to infected pets, as the owners are often in close contact with them. They are also usually caused by scratches or bites from wild or pet animals.

indirect contact

The contact does not occur with the animal, but with the areas and surfaces in which it is found. By moving, the animal has left its germs on the objects in the environment, and a human touching them allows the pathogen to reach his body.

The most typical ways to get it this way is getting into pet habitats, on farms, on the ground where animals graze, and touching bowls where pets eat and drink.

Through vectors

This includes all those diseases that we get when we get bitten by a tick or a flea or bitten by a mosquito.


Eating contaminated food is one of the leading causes of illness in the world. When we eat something that comes from an animal with germs, these can reach our interior. Hence the importance of food safety and cooking food correctly at home.

The most typical forms of contagion are the consumption of raw meat with pathogens, unpasteurized milk, undercooked eggs, and fruits and vegetables contaminated with feces from sick animals.

The 20 most important zoonoses in the world

Having already defined what a zoonosis is and how it can occur, we present below some of the most common animal-borne diseases in the world , analyzing their causes and symptoms.


Rabies is a disease caused by a virus of the Rhabdovirus family that is transmitted by dogs, cats and rodents and reaches humans by direct contact, usually a bite.

The symptoms are as follows: excessive salivation, hallucinations, insomnia, facial paralysis, fever, vomiting, hydrophobia (fear of water), confusion, hyperactivity, etc.

Once the person begins to show symptoms, there is little to do, because the disease ends up being fatal. That is why people at risk of contagion should be vaccinated to avoid this infection.

Cat scratch disease

Cat scratch disease is, as its name suggests, a zoonosis that is caused by direct contact due to a cat scratch, usually from kittens. It is caused by a bacterium called “Bartonella henselae”.

The symptoms are the following: appearance of bumps or blisters at the site of the injury, swollen lymph nodes, malaise, fatigue and sometimes fever. Unless the immune system is weakened, this disease is usually not serious and antibiotic treatment is sufficient.

Lyme disease

Lyme disease is a zoonosis caused by the bite of a tick, which can infect us with four different types of bacteria depending on the geographical area, although it is usually present only in areas with a lot of forest.

The first symptom is the appearance of a small red bump at the site of the bite. After several days, it expands in the form of a rash and reaches more than 30 cm. This phase is usually accompanied by fever, fatigue, chills and neck stiffness. Antibiotic treatment is effective in preventing the development of more serious complications.


Ringworm is a disease caused by a fungus that can be spread in many different ways. One of them is through a zoonosis process, with pets (and especially cats) being the most common carriers.

The fungus affects the skin, and its symptoms depend on the infected part of the skin, although it is usually characterized by the presence of scaly areas on the skin. It does not tend to lead to more serious diseases since the fungi do not usually pass beyond the skin, although there are antifungal creams that kill the pathogen.


Campylobacteriosis is a very common zoonosis that usually reaches humans through the consumption of contaminated food, especially raw or undercooked poultry. It is caused by the bacterium “Campylobacter”.

Although sometimes there are no symptoms, when they do appear they do so between 2 and 5 days after consuming the meat and are usually the following: diarrhea (sometimes bloody), cramps, fever, nausea, vomiting, abdominal pain , fatigue, etc It often heals on its own, although in more severe cases it can be treated with antibiotics.


Leptospirosis is a zoonotic disease caused by a bacterium called “Leptospira” that reaches people generally through the consumption of water contaminated with urine from infected animals, although it can also happen through direct contact.

The symptoms, which can take up to a month to appear, are the following: nausea, vomiting, diarrhea, muscle pain, fever, dry cough and headache. Antibiotic treatments are effective in eliminating the bacteria and serious complications such as meningitis are a voided.


Toxoplasmosis is a zoonotic disease caused by the parasite “Toxoplasma gondii”, which reaches humans through different animals. People can become infected by indirect contact with pets (especially cats) or by eating raw meat from contaminated lamb or pork.

There may be no symptoms, although when there are they are the following: swollen lymph nodes, headache, fever, muscle pain, sore throat, etc. People without symptoms do not require treatment, as they end up remitting on their own, but there are medications that kill the parasite.


Leishmaniasis is a zoonotic disease caused by a protozoan (unicellular organisms) that is transmitted to humans through the bite of female blackflies, a species of insect similar to mosquitoes but with a rounder body.

The symptoms of this disease are the following: appearance of sores on the skin, congestion and nosebleeds, difficulty in swallowing and breathing and development of ulcers in the mouth. Medication treatment is effective, although facial surgery may be required if the sores on the face have caused many problems.


Scabies is a dermatological disease caused by “Sarcoptes scabiei”, a small mite that is transmitted by skin-to-skin contact between humans but can also be spread through animals.

The main symptomatology of scabies is intense itching in the areas of the skin that the mite has bitten, which increases at night. The treatments are applied on top of the skin itself and manage to eliminate the parasites and their eggs.


Salmonellosis is a zoonotic disease caused by the “Salmonella” bacteria, which reaches people after consumption of water or food (eggs and red or white meat) contaminated by feces from infected animals.

There are not always symptoms, although the bacteria can cause gastroenteritis with the following symptoms: vomiting, nausea, diarrhea, fever, blood in the stool, chills, abdominal cramps, headache, etc.


Hydatidosis is a zoonotic disease caused by a helminth (similar to worms) known as “Echinococcus granulosus”, which reaches humans through direct contact with infected dogs or by ingestion of vegetables or water contaminated with parasite eggs.

When the parasite infects humans, it generally travels to the lung or liver and becomes encysted, giving rise to a hydatid cyst. This may not give symptoms until after 10 years, although in the end it causes the following: if it is in the lung, bloody sputum, cough and chest pain; if it is in the liver, abdominal pain and swelling of the abdomen. Antiparasitic medications are effective, although if the cyst is too large it may require surgery.


Malaria is a zoonotic disease caused by the “Plasmodium” parasite, which reaches humans through the bite of a mosquito.

It almost exclusively affects the African continent, where the parasite infects more than 200 million people each year and is responsible for some 400,000 deaths.

Its most common symptoms are the following: anemia (since the parasite infects red blood cells), fever, chills, blood in the stool, seizures, vomiting, nausea, diarrhea, etc. Hospitalization is essential, otherwise it can end up causing multi-organ failure that leads to coma and ultimately death.

Yellow fever

Yellow fever is a zoonotic disease transmitted to humans also by the bite of a mosquito, although in this case the causal agent is a virus. It is common in South America and sub-Saharan Africa.

The symptoms are as follows: fever, headache, arrhythmias (heartbeat irregularities), delusions, seizures, decreased number of urinations, red eyes, face and tongue, etc. Like malaria, without prompt application of appropriate treatment, yellow fever is often fatal.

Bovine spongiform encephalopathy

Bovine spongiform encephalopathy, popularly known as “mad cow disease”, is a zoonotic disease caused by the consumption of beef (especially nervous tissue) contaminated with prions, proteins with infective capacity. It is currently very rare, although due to its fame and seriousness, it deserves to be mentioned.

The disease causes a degeneration of the brain with the following symptoms: dementia, walking problems, lack of coordination, muscle stiffness, spasms, personality changes, drowsiness, difficulty speaking, etc. It inevitably ends up being deadly.

Mediterranean boutonneuse fever

Mediterranean boutonneuse fever is a zoonotic disease caused by the bite of a tick, which infects humans with a bacterium of the genus “Rickettsia”. Pets, especially dogs, often carry these ticks and allow them to come into contact with people.

In recent years, the incidence is increasing especially in the south of France and Spain. The initial symptoms consist of a dark lesion at the site of the bite, but after a few weeks fever, headache, joint discomfort, muscle pain and skin rashes begin. It does not have serious health consequences, although antibiotic treatment helps treat this disease.


Ehrlichiosis is a zoonotic disease caused by the bacterium “Ehrlichia canis”, which is transmitted to humans by the bite of a tick usually carried by dogs.

The symptomatology is similar to that of the flu and consists of: skin rash at the site of the bite, low-grade fever, headache, chills, diarrhea, loss of appetite, confusion, cough, headache and muscle pain, etc. . Antibiotics are helpful in treating the disease.


Toxocariasis is a zoonotic disease caused by a parasite and is spread by indirect contact (usually on the floor of the house) with pets. The dog transmits the parasite “Toxocara canis” and the cat, “Toxocara cati”.

Once in the human, the larvae migrate to different organs: lungs, liver, kidneys, muscles, heart… The symptoms depend on where the parasite is located, but it is due to the fact that it causes inflammation of these organs. When it migrates to the eye, the parasite can be seen with the naked eye and may cause vision loss. There are medications that can kill this parasite.


Anthrax is a disease caused by “Bacillus anthracis”, a bacterium that gained fame as a result of the bioterrorist attacks at the beginning of the century in which this germ was spread through the mail in the United States. 5 people died.

Humans can accidentally become infected by direct contact with animals or by eating meat contaminated by the bacteria. The symptomatology will depend on the form of contagion, as it can be cutaneous (due to a skin wound), by inhalation (the most dangerous since it affects the respiratory system) or gastrointestinal (due to the consumption of contaminated meat).

Antibiotic treatment is effective. The problem is that many people don’t realize they have the disease until it’s too late, at which point anthrax is deadly.

Bird flu

Birds also suffer from flu. It does not usually affect humans, although there have been epidemics of avian influenza in humans due to transmission of the virus by direct contact with infected birds or by consumption of their raw or poorly cooked meat (or eggs).

The 2009 influenza A pandemic is one of the most famous zoonotic diseases and ended up causing the death of some 18,000 people.

Symptoms include: cough, sore throat, fatigue, muscle pain, red eyes, nasal congestion, shortness of breath, etc. The disease can be fatal but only in people with a weakened immune system or in people over 65 years of age. There is no cure, although treatment with antivirals can reduce the severity of symptoms.

Sleeping Sickness

Sleeping sickness is a zoonosis caused by parasites of the genus “Trypanosoma”, which reaches humans through the bite of the tsetse fly, which is found only in Africa.

The symptoms of the disease are as follows: uncontrolled sleepiness during the day and insomnia at night, anxiety, excessive sweating, headache, weakness, fever, etc. There are medications to treat the disease, though people who don’t have access to them can end up in a coma and eventually die.

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