The coexistence of man with other species has the same background as humanity. Since domestication, we have used them for food, clothing, work, companionship, research, rescue, recreation, among many other activities. Nowadays, dogs and cats coexist closely with us, mainly as pets, without ignoring that they provide many other services of great importance, in addition to companionship.

The purpose of the article is to point out a negative aspect of this relationship, that is, that dogs and cats are capable of transmitting diseases to humans, called zoonoses, and of causing more or less serious injuries, such as bites and scratches. Also, to point out some concepts of health, prevention, and natural and acquired defenses to avoid diseases.

We all understand that if animals and humans are healthy, it is not possible for diseases to be transmitted between them, and health should be a fundamental right and a social goal. Having lived together for so long is the clearest evidence that life in interspecific communities is possible if proper disease prevention and control measures are taken.

The causes by which man or animals are susceptible to the disease are varied and depend on the individual (host), the causal agent, or the environment. In the absence of one of them, the disease does not occur, therefore, it is necessary to know them, to identify them, because the preventive measures are directed towards one of these causes, with the purpose of decreasing its incidence and facilitating its eradication.

Zoonoses are infectious diseases of animals that are transmissible to humans and other animals under natural conditions, directly by contact with the animal or indirectly through vectors or vehicles.

Biological agents causing disease

The following are the diseases that can be transmitted from dogs and cats to humans and their biological causative agents:

Protozoa are unicellular, non-photosynthetic microorganisms, from which the amoeboid and ciliate types are derived. Amebiasis, Giardiasis, Toxoplasmosis, Leishmaniasis, Trypanosomiasis.

Bacteria are unicellular microorganisms, excluded from the animal and plant kingdom because they are in an intermediate stage between the two. They produce disease by direct invasion of tissues or by means of toxins. Anthrax, Brucellosis, Cat scratch fever, Leptospirosis, Listeriosis, Bites, Salmonellosis, Tuberculosis, Nocardiosis. Anthrax, lesions with possible infection by bite, and cat scratch fever are not zoonoses per se. They should be considered as public health problems.

Mycoplasmas are pleomorphic microorganisms that lack a cell wall.

Rickettsiae and Chlamydias are obligate intracellular microorganisms, intermediate between viruses and bacteria, transmitted by arthropods in which they live and spread without harming them. Spotted fever.

Viruses are the smallest structures capable of producing disease, they only reproduce in living tissues. Rabies.

Fungi. True fungi are characterized by the formation of filaments whose ramifications form a dense colony or mycelium. Fungi are identified by the type of colony and by the type of spore produced by the mycelium.

Arthropods. Fleas. Sarcoptic mange, Linguatulidosis.

Cestodes. Echinococcosis, Cenurosis, Diphyllobothriasis, Diphylidiasis.

Nematodes. Dirofilariasis, Gnathostomiasis, Renal helminth infection, Theraziosis, Toxocariasis, Ancylostomiasis, Strongyloidosis.

Factors involved in the emergence and spread of an infectious disease

To understand the factors involved in the emergence and spread of infectious diseases, it is necessary to know the following conditions.

Endemic or enzootic: The usual presence of an infectious agent in a geographical area or the prevalence of a disease in a circumscribed area. Endemic is the term applied to humans and enzootic to animals.

Epidemic or epizootic: Occurrence of a disease or outbreak that clearly exceeds the normal expected incidence.

Outbreak: Two or more cases that are related to each other and occur in an area where the disease is controlled or eradicated.

Host: This term is given to any animal that under natural circumstances allows the subsistence or lodging of an infectious agent.

Reservoir: Any living being, soil, or inanimate matter in which an infectious agent normally lives and multiplies and on which it depends to survive by reproducing or conserving the capacity to be transmitted to a susceptible organism. It is of great importance to know the reservoirs because most of the disease control measures are aimed at controlling the reservoirs of the agents that cause them.

Source or focus of infection: Any living thing, object, or substance from which the infectious agent can pass to the susceptible organism.

Transmissibility period: The time in which an infectious agent can be transmitted directly or indirectly from one person or animal to another.

Carrier: An infected person or animal that has the specific infectious agent of a disease and that constitutes a potential source of infection for other animals or humans, regardless of whether or not the animal presents a clinical disease. When the carrier is not infected, it is called a healthy carrier; if it is capable of infecting before the disease occurs, it is called an incubating carrier; and finally, a convalescent carrier when the patient is in full recovery from the disease and is capable of transmitting it.

Host defense mechanisms

The factors can be summarized as follows.

Agent factors - Biological, Physical, Chemical.

Host factors - Genetic Load, Age, Sex, Nutritional Status, Immunity (Nonspecific, Natural or Innate, Acquired).

Environmental factors - Physical, Biological, Social.

Among the host characteristics that allow the host to defend itself from the environment are the following:

Genetic load: Many traits determined by the ethnic group to which the dog and cat belong as well as the breed and/or family may in certain circumstances include greater or lesser susceptibility to certain diseases.

Age: Chronological age is a factor in the presentation of infectious and non-infectious diseases. During the course of an individual's life, the immune response changes, with the young and the old being the most susceptible.

Sex: With respect to sex, some communicable diseases are more frequent in one sex than in the other.

Nutritional status: Diet is an important factor because, in a malnourished or undernourished individual, resistance to disease is reduced; on the contrary, a balanced diet contributes to greater resistance to disease.

Immunity: Immunity or resistance should be understood as the sum of all physiological processes that allow an animal to recognize foreign substances to its organism and eliminate, neutralize or metabolize them. Immunity does not determine that an individual is permanently protected from any disease; it depends on the concentration and virulence of the infecting organism, the individual's resistance, or previous exposures.

Natural or innate immunity refers to all non-specific defenses of the individual, does not depend on previous exposure to a foreign agent, prevails under any circumstances, and prevents foreign agents from harming the individual. The mechanical, physical, and chemical action of these defenses against pathogens prevents animals and humans from getting sick but can be weakened by factors such as poor nutrition or stress.

Acquired immunity depends on a previous exposure of the organism to the pathogenic agent and its subsequent recognition and elimination. It is characterized by being inducible, specific, having memory, and occasionally by being transmissible. It is the principle of vaccinations.

General recommendations

It is recommended that people who are or have been in contact with a dog or cat positive for any of the aforementioned diseases, should visit their family physician so that he/she can take the appropriate measures. All people who live or work with animals should follow the following recommendations.

Annual vaccination of dogs and cats against rabies.

Periodic medical examination of pets, including stool parasite examination.

Disinfection of examination equipment and use of gloves or handwashing between the examination of one patient to another. Use sterile material for these examinations.

Do not sleep with pets and avoid the proximity of the face with the respiratory tract and muzzle of animals.

Wash hands before eating and after going to the bathroom or when returning from playing in areas where animals live.

Use footwear, especially when dealing with dirt floors.

Hygienic measures with animals such as bathing every 3 or 4 months and rinsing with water every 15 days. Continuous cleaning of excreta and administration of water and food in clean and clean areas for this purpose.

Do not feed raw or undercooked fish, meat, or offal to animals, a recommendation that is also advisable for humans to follow.

Avoid overcrowding among animals and between animals and humans.

Author: Carlos Manuel Appendini Tazzer