What parasitic diseases can animals transmit to us?

Parasitic zoonoses are diseases caused by parasites transmitted from animals to man and vice versa. The common routes of infection are direct contact, ingestion of infective forms, foodborne transmission, or the bite of an insect vector.

As a definition, parasites are eukaryotic beings that live at the expense of other organisms they invade. They are classified into three large groups: protozoa, helminths (trematodes, cestodes and nematodes) and arthropods. In addition, depending on their location they can be endoparasites (tapeworms) or ectoparasites (ticks, fleas).

The impact of the various parasitic zoonoses is variable, depending on the prevalence and severity of the pathology they produce. The distribution and endemicity is related to the different environmental conditions in different areas of the world, socioeconomic characteristics and population habits.

The list of notifiable diseases includes some of these parasitic zoonoses, while others are not subject to surveillance, making it difficult to determine their impact. This article collects the parasitic zoonoses of compulsory declaration in Spain.


It is caused by the protozoan Cryptosporidium parvum, which affects humans and young calves and lambs. There is another kind Cryptosporidium hominiswhich almost exclusively infects humans.

This microorganism is transmitted by the fecal-oral route, by ingestion of infectious oocysts, direct contact with infected people or animals, or by contaminated water and food. Their cysts can survive for months in moist soil or water and withstand harsh environmental conditions for long periods of time.

The disease can be asymptomatic or cause intestinal discomfort with diarrhea. It usually resolves spontaneously, but in immunosuppressed people it can develop severe symptoms and be life-threatening.


Infestation by the protozoan called Giardia lamblia, Giardia intestinalis either Giardia duodenalis It affects both humans and animals (dogs, cats, cows and sheep). In the environment, the main reservoirs of the parasite are surface waters.

Giardia cysts can survive for long periods of time in the environment, and chlorination of water alone cannot inactivate them. It is transmitted by personal contact with infected patients or animals or by exposure to contaminated food or water. Babies and children are at particularly higher risk of infection.

Infected people may remain asymptomatic or develop acute or chronic diarrhea. Bloating, fatigue, and malabsorption of vitamins and fats may also occur.

Giardia lamblia.
Eva Nohýnková, Charles University, CC BY

hydatid disease

This zoonotic disease is caused by the larval stage (hydatid cyst) of the tapeworm. Echinococcus granulosus. The adult forms live in the intestine of the definitive host, the dog (also foxes), which excretes eggs with the faeces. Those eggs can be ingested by the intermediate hosts, sheep, goats, pigs and humans.

The eggs hatch and release the larvae in the duodenum, which cross the intestinal barrier and migrate to certain organs (liver, lung, kidney, brain) where they will form cysts. Dogs become infected by ingestion of raw viscera of cyst-infected intermediate hosts.

Poor hand hygiene, close contact with infected animals, and consumption of unwashed and poorly cooked food contaminated with echinococcus eggs (eg, vegetables) are risk factors. Apart from better cleaning food and cooking meat, regular deworming of dogs and correct elimination of their feces are a tool for the prevention of hydatid disease.

The symptoms are different depending on the affected organ and are manifested due to the increase in size of the cysts. Treatment, depending on the case, may require surgery and the use of specific anthelmintic medications.


This disease is caused by protozoa of the genus Leishmaniasis It is transmitted by the bite of mosquitoes of the genera Phlebotomus (Europe, Africa and Asia) or Lutzomyia (America). The reservoirs are mainly dogs, but also other mammals.

Leishmaniasis manifests itself in different ways. The cutaneous form causes skin sores that often heal on their own within a few months. The mucocutaneous form produces deeper lesions at the mucosal level. Visceral leishmaniasis causes a systemic disease that presents with fever, malaise, weight loss, and anemia, swollen spleen, liver, and lymph nodes.

The best way to prevent leishmaniasis is to avoid exposure to the vector, early diagnosis and proper management of cases, both in humans and domestic animals that act as a reservoir, and through vector and zoonotic reservoir control measures. There are drugs to treat it, but there are no vaccines marketed for humans. There are only vaccines against canine leishmaniasis, although their efficacy is still controversial.


Cats are the main reservoir of the parasite that causes this disease, which is the protozoan Toxoplasma gondii. These microorganisms excrete cysts into the environment capable of infecting many animals and humans. Toxoplasma cysts can survive in the environment for a long time.

Infection occurs by eating undercooked meat infected with cysts (especially pork and lamb), by ingesting cysts present in contaminated food (poorly washed vegetables) or water, by ingestion of infected cat feces, or by direct mother-to-child transmission During pregnancy.

The infection usually does not produce symptoms in humans or they are very mild. However, the disease can be serious in immunocompromised people or if it occurs during pregnancy. In congenital infections, the parasite can cause eye or brain malformations (with disabling effects on the individual) or result in miscarriage or perinatal death. Congenital toxoplasmosis is preventable through gestational screening and the adoption of prophylaxis measures.

Parasites wrapped in a circular bag seen under a microscope.
Microscopic cyst of Toxoplasma gondii developed in the brain of a mouse.
Jitinder P. Dubey/USDA

trichinellosis or trichinosis

It is a zoonosis caused by nematodes belonging to the genus Trichinella, a parasite that is initially located in the intestine and gives rise to a new generation of larvae that migrate to the muscles, where they encyst. Many animals can act as reservoirs, but the most frequently implicated in cases of human infection are pigs, horses and wild boar.

The infection occurs exclusively through food, through the consumption of raw or undercooked meat that contains the larvae of the parasite. In humans, the clinical picture varies from asymptomatic cases to particularly severe cases and even deaths. Classic symptoms are characterized by diarrhea, muscle pain, weakness, sweating, swelling of the upper eyelids, photophobia, and fever.

There are antiparasitic drugs to treat the infection. Prevention of trichinosis is based on accurate inspection of all slaughtered pigs and horses, which is mandatory in Europe. Imported and bushmeat pose a higher risk and should be discouraged from being eaten raw or undercooked.

Diseases transmitted by lice and ticks

The list of notifiable diseases in Spain also includes other zoonotic diseases that are transmitted by ectoparasites such as ticks or lice, but whose causal agent is actually a bacterium (genera Rickettsia, borrelia) or virus (Flavivirus). These are tick-borne encephalitis, tick-borne relapsing fever, and Mediterranean spotted fever.

Transmission generally occurs when the ectoparasite feeds on an infected animal (with these viruses or bacteria) and then feeds on a human, inoculating viruses or bacteria in the process, which are the ones that will cause the disease.

Millions of cases in the world

The number of confirmed cases in Europe of parasitic zoonoses can range from a hundred (trichinosis) to more than 14,000 and 19,000 (cryptosporidiosis and giardiasis, respectively). Cases of leishmaniasis or congenital toxoplasmosis are around 200 per year and hydatid disease 400.

In other countries, leishmaniasis and hydatidosis are included among the so-called neglected diseases, which are a set of infectious pathologies (caused by viruses, parasites and bacteria) that affect the poorest populations and those with limited access to health care.

It is estimated that each year there are between 700,000 and 1 million new cases of leishmaniasis in the world, while the prevalence of hydatid disease in some areas reaches 10%. It is estimated that the sum of the annual costs of treating hydatid disease and the losses to the livestock industry amounts to 3 billion dollars (about 2.95 billion euros).

Preventive measures

Prevention depends on the type of parasite and its form of transmission. In addition to the specific indications for each one, special attention must be paid to cleaning vegetables, eating raw vegetables and cooking meat, which must be eaten well cooked. Methods such as salting, curing, smoking, and marinating are not effective treatments for destroying parasites or cysts.

Likewise, it is important to follow basic hygiene rules such as washing your hands before eating and after going to the bathroom.

Proper water management and treatment is also essential. The use of animal excrements as fertilizer should be avoided, and in general handle the excreta of domestic animals with care and prevent children from coming into contact with them.

Related articles

The year is ending! These are the holidays for December 2023

By Yulexy AuquillaDecember 1, 2023 at 5:46 p.m.2023 is almost over and the last month of the year is always full of parties,...

New York: it hasn’t snowed in a long time and experts are already predicting...

NY It is one of the cities that can be seen the most in series and movies. Surely every person in the world...

Bukele takes leave of office to seek re-election

The Congress of El Salvador approved that Claudia Juana Rodríguez de Guevara, current private secretary of Nayib Bukele, occupy the Presidency while the president...

The cynical message from a Chinese ambassador for Javier Milei’s decision to “get out”...

After the sayings of Diana Mondinofuture chancellor, who assured that Argentina will not integrate the BRICS, the Chinese ambassador to Colombia, Zhu Jingyang,...