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Zoonoses are infectious diseases that can be transmitted between vertebrate animals and humans. Understand and check examples

Edited and resized CDC image is available on Unsplash

Zoonoses are infectious diseases transmitted from animals to humans and vice versa. the word comes from the greek zoon, which means animal, and ours, illness. The World Health Organization (WHO) defines zoonoses as “naturally transmissible diseases or infections between vertebrate animals and humans”.

Classification

More than 200 communicable diseases fit the definition of zoonosis proposed by the World Health Organization. Two classifications were created to facilitate the study of this group of diseases, according to their transmission modes or pathogen life cycles.

Classification as to the mode of transmission

• Anthropozoonosis: diseases that are perpetuated by transmission between animals, but can eventually affect humans.
• Zooanthroponoses: diseases that are perpetuated by transmission between human beings and may eventually affect animals.
• Anfixenosis: diseases that are transmitted with equal intensity between animals, humans and also between animals and humans.

Examples

Anger

Anthropozoonosis caused by the contact of human beings with the saliva of animals contaminated by the virus that causes rabies, scientifically called Lyssavirus. Transmission occurs mainly from animal bites, but it can also happen from scratches and licks. The main symptoms in humans are fever, headache, excessive salivation and muscle spasms.

bovine tuberculosis

Zooanthroposis caused by infectious agents Mycobacterium tuberculosis and Mycobacterium bovis, family bacilli Mycobacteriaceae. The first species has human beings as its only host, while the second affects both bovine animals and human beings. Transmission can happen through contact with secretions containing the tuberculosis bacilli or through consumption of contaminated food.

The main symptoms in humans are local pain, cough, fever and fatigue. In cattle, the disease causes damage to various organs and tissues, such as lungs, liver, spleen and even carcasses.

Staphylococcosis

Anfixenosis caused by bacteria of the genus Staphylococci. Transmission can occur directly, through contact with an individual or objects contaminated by the bacteria, or indirectly, through the ingestion of foods that contain the pathogen. The main symptoms are malaise, fever and headache.

Classification according to pathogen maintenance cycles

• Direct zoonoses: the pathological agent can persist with successive passages through a single vertebrate animal species;
• Cyclozoonosis: the agent must pass through two distinct species of vertebrate animals for its cycle to be completed;
• Metazoonosis: the agent must pass through an invertebrate host for its cycle to complete;
• Saprozoonosis: before causing infection, the pathological agent needs to undergo changes that occur in the external environment.

Examples

In addition to anthropozoonosis, rabies is also classified as direct zoonosis.

Cysticercosis

Cyclozoonosis caused by the larvae of two tapeworm species, Taenia solium and Taenia Saginata. Transmission occurs mainly through the consumption of contaminated water and food. The main symptoms are pain in the abdomen, nausea, vomiting and headache.

Chagas disease

Metazoonosis caused by the protozoan trypanosoma cruzi. Transmission occurs through contact with the feces of the transmitting agent, the stink bug known as "Barber", which causes itching and irritation when deposited on human skin, facilitating the entry of the protozoan into the body. The contagion can also happen through the ingestion of contaminated food or water vertically, from mother to child, or by blood transfusion. The main symptoms are fever, swelling of the lymph nodes, heart palpitations and pain in the abdomen and muscles. If left untreated, it can cause an increase in the size of the liver, spleen and heart, among other complications.

toxoplasmosis

Saprazoonosis caused by the protozoan Toxoplasma Gondii, found in the feces of cats and other felines, which can lodge in humans and other animals. The infection can be caused by eating raw or undercooked meat from contaminated animals, such as cows and pigs, or by consuming water, fruits and vegetables that contain eggs of the protozoan.

Contaminated utensils can also carry eggs to other foods, a phenomenon known as cross-contamination. Find out how to avoid cross-contamination in the article: “What you need to know about cross-contamination”.

Toxoplasmosis can be transmitted congenitally, that is, from mother to fetus, but it is not transmitted from one person to another. Its main symptoms are fever or fatigue, muscle pain and swelling of the nodes.

Other examples of zoonoses

Hookworm or geographic bug

Infection caused by the larvae of parasites that live in the intestines of dogs and cats. There are two main species of geographic beast, the brazilian ancylostoma it's the Ancylostoma caninum, whose eggs are released in the feces of these animals. These eggs hatch in the soil and release larvae, which can easily enter the skin of people who have direct contact with the feces of these animals. The main symptoms are irritation and itching.

salmonellosis

Infection by salmonella, a genus of pathogenic bacteria, is called salmonellosis. Contact with infected animals and people, food and objects contaminated by the bacteria are the most common forms of transmission. The main symptoms are loss of appetite, diarrhea, abdominal cramps, chills and fever.

leptospirosis

Infection caused by a bacterium of the genus Leptospira and transmitted by animals of different species - rodents, pigs, dogs, cattle. The contagion occurs through direct contact with the urine of infected animals or through exposure to contaminated water, which enters the body through mucous membranes and intact skin or with small wounds, and spreads into the bloodstream. The main symptoms are high fever, muscle pain, urinary and liver changes.

Yellow fever

Infectious disease caused by a virus, scientifically called Flavivirus. Its transmission occurs through the bite of transmitting mosquitoes, which act as intermediate hosts. Yellow fever has epidemiological importance due to its clinical severity and potential for dissemination in urban areas infested by the mosquito. Aedes aegypti, transmitter of other diseases such as dengue, Zika and chikungunya. The main symptoms are fever, chills, headache, body aches and fatigue.

Psittacosis

Infectious disease caused by bacteria of the genus Chlamydia. Parrots (parrots, macaws and parakeets) are the main hosts of these bacteria, but species such as pigeons, geese and turkeys can also be contaminated. Psittacosis is transmitted through the aspiration of dust contaminated by the excreta of sick or carrier animals. The main symptoms are fever, cough and chills.

Zoonoses transmission

Zoonoses are caused by pathogens such as bacteria, fungi, viruses, protozoa and parasites, as seen in the examples cited above. Vertebrate and invertebrate animals can serve as definitive or intermediate hosts for these agents, depending on their maintenance cycle.

The transmission of zoonoses can occur directly, through contact with secretions (saliva, urine, feces or blood) or through scratches and bites from contaminated animals. Indirectly, it occurs through vectors, such as mosquitoes, and through the consumption of water or food contaminated with pathological agents.

Prevention of zoonoses

Health education, environmental management and animal vaccination are the main forms of prevention against zoonoses, according to the Ministry of Health's Manual on surveillance, control and prevention of zoonoses. the society. It is necessary, however, to prioritize the most vulnerable locations, working in schools and other places where the target audience can be reached. Environmental management, in turn, is based on actions carried out by environmental agencies to control or eliminate possible vectors of disease transmission.

Finally, it is extremely important to carry out anti-rabies vaccination of dogs and cats, as recommended for each region in the Ministry of Health's National Rabies Surveillance and Control Program.