Zoonosis Aspects to Consider for Its Approach

Abstract

This paper constitutes a compendium of introductory aspects to consider the approach to zoonosis useful for health sciences professionals. It was based on a documentary review of scientific literature based on a narrative approach. The information found was grouped into the following chapters: the concept of zoonosis, general aspects of zoonosis, an overview of zoonosis in the world, and theoretical and methodological interventions on zoonosis. Finally, and as a contribution from the researchers, conclusions are provided.

1. Introduction

Zoonosis (due to viruses [45%], bacteria [28%], parasites [20%], and fungi [7%]) cause damage to health because they represent 70% of the infectious pathologies that affect human beings and with a significant compromise of animal health (of 1 415 pathogenic agents for humans, 868 zoonosis have been described, and 80% of the latter are capable of affecting different species of animals), which implies a considerable economic burden for the countries, fundamentally derived from their health system [1, 2, 3].

In addition, the underreporting of zoonosis in many countries, especially those with low incomes, is notable, among other things, to deficiencies in health promotion and education, poor health coverage, limited hospital and laboratory infrastructure, poor inter-institutional interaction and, especially the application of deficient sanitary control programs [4, 5].

These diseases are often underestimated as a public health problem despite their significant impact on morbidity and mortality (43.6% are distributed throughout the world, of which 63.3% appear in Africa) compared to other pathologies that affect humans and animals [3, 6, 7, 8, 9].

Mainly due to the lack of knowledge of the real magnitude of the problem (good records are not kept), the noncompliance in the application of the control programs that already exist in each country, and because of the key concepts that constitute the theoretical framework of zoonoses as an area of knowledge They are scattered in various bibliographic sources, which makes access difficult [3, 6, 7, 8, 9].

The objective of the present written is to make a compilation of information on the last point, that is, a concentration and updating of relevant aspects that exist in the world literature on the subject based on a narrative approach. Since solid knowledge is that health professionals can achieve significant achievements in the prevention, control, and eradication of zoonosis [3, 6, 7, 8, 9].

2. Methodology

The present work was based on the documentary review of scientific literature in electronic and physical format on aspects of zoonosis based on the systematic analysis and narrative description of what was found, for which virtual databases were used (Bireme/PAHO, Medline, PudMed, and Scielo) from descriptors related to the topic. Repeated documents and those without clear conclusions and without originality were excluded. All original articles published up to December 2021 were included. The relevant ideas were grouped into four aspects that can be read independently, in order to facilitate their review:

1. The concept of zoonosis,

2. General aspects of zoonosis,

3. Overview of zoonosis in the world, and

4. Theoretical and methodological interventions of zoonosis.

Finally, and as a contribution from the researchers, conclusions are provided.

2.1 The concept of zoonosis

This word derives from the Greek roots zoos (animal) gnosis (disease). Its origin is attributed to Rudolf Virchowe, since in the nineteenth century he used this word to refer to diseases shared between man and animals. In 1956 (in the twentieth century) the World Health Organization defined zoonosis as any disease that is naturally transmitted from vertebrate animals to man in a man-centered concept, therefore, three years later this international organism of health reformulates the concept of diseases that are transmitted between animals and man [10, 11].

This last definition of zoonosis is followed by the proposal by Schwalbe, which from the operational-administrative perspective gives it the following meaning: “… those infections and infestations that in nature are shared by man and other lower vertebrate animals” [10, 11, 12]. Subsequently, the concepts zoo anthropozoonosis (when the infection is transmitted from animals to humans) and anthropozoonosis (when the infection is transmitted from humans to animals) appear [11, 12].

According to the characteristics of their transmission cycle, zoonosis is classified into (Table 1):

Transmission cycle	Type
Direct cycle	Only one vertebrate involved.
Cyclozoonosis	More than one vertebrate is involved.
Metazoonosis	A vertebrate and an invertebrate participate.
Saprozoonosis	Requires an inert element to complete its transmission cycle.

Table 1.

Types of zoonosis according to their transmission cycle.

Source: Schwalbe (10), Acha (1986), Bastidas (2018).

In addition, the transmission of a zoonosis between animals and humans can be:

• Direct due to systematic or circumstantial coexistence (they group together a large part of the best-known zoonoses);

• Indirect when different elements of the environment, such as soil, water, organic matter, food, and vectors (abundant in etiology and versatile in their form of transmission), intervene;

• Those that can be transmitted directly or indirectly [10, 13, 14].

2.2 General aspects of zoonosis

Due to their form of transmission, zoonosis is divided into:

• Direct (they are transmitted by contact between vertebrate animals and humans, and vice versa), and

• Indirect (includes living or inanimate intermediaries).

They can also be

• Emerging (unknown so far or the result of infection) evolution or modification of pathogenic agents whose pathogenicity, transmitter, or host is known),

• Re-emerging (these are known diseases whose prevalence increases considerably), or

• Exotic (known but never before presented in a certain region).

A disease can be placed in more than one category. In addition, these infections can be:

• Synanthropic (urban cycle) or

• Exoanthropic (sylvatic cycle), and

• Even be mixed [15].

Emerging and re-emerging zoonosis are considered neglected diseases because their prevalence is particularly high in marginalized populations with low incomes without access to health services and where official health institutions neglect to attend to their health needs. In addition, among the conditioning factors of the emergence and re-emergence of zoonosis, demography, ecological and climatic changes, and human behavior are mentioned [16, 17].

2.3 Overview of zoonosis in the world

The key element to describe the epidemiological behavior of zoonosis is the information registry. However, its quality (complete and up-to-date) can be seriously compromised in countries with low economic income, due to poor investment of financial resources and technical difficulties, as well as the frequent political and social conflicts that occur in many of these countries, because private health institutions do not keep records or do so partially or incompletely, and because of the subclinical behavior of some zoonosis that prevents their registration on time [6, 18, 19].

In countries with low economic income, economic support, and the availability of human talent and favorable political will toward the health sector are constantly changing, which has a negative influence on the control and eradication of zoonosis, since they mark periodic cycles of advances and setbacks in the fight with these diseases. Likewise, the scarce or absent intersectoral coordination and the non-perception of zoonosis as an important public health problem by health authorities contribute to the stagnation in the control of these diseases. The need for care and the institutional response to zoonosis control allow it to be grouped into three categories as shown in Table 2 [6, 20]:

Zoonosis	Health action
With significant morbidity and/or mortality	It is present in the epidemiological records.; With a sanitary control and epidemiological surveillance program incorporated into the organizational structure of the country’s health system.; With technical regulations and legal framework.; With infrastructure and financing.
Sporadic outbreaks, but in longitudinal follow-up, they are more or less frequent.	With direct or indirect evaluations of its incidence by not necessarily official institutions of the health sector.; They lack health control programs.
Rarely therefore its importance for public health is unknown.	They are recorded as isolated and insignificant events, generally by private care services.

Table 2.

Zoonosis according to its importance, is a health problem.

Source: Modified from Matamoros [6].

The control and eradication of zoonosis are seriously compromised by a series of factors that ensure their spread, among which are mentioned:

• The ability of some pathogens to infect a wide variety of species,

• The appearance of new zoonosis,

• Immunosuppression of the susceptible (due to chemotherapy, use of steroids, and HIV),

• The tendency of the diseases to remain in a latent or subclinical phase,

• The chronic course of many of them,

• The damage to health and the severe economic losses that they produce,

• The complexity of the re-emergence of multiple zoonosis,

• The underestimation of clinical diagnosis and the frequent disarticulation between human and animal health in the approach to zoonosis [21, 22, 23, 24].

In addition, the control of zoonosis is affected:

• By not being addressed in a particular way despite the existence of common elements,

• By the constant demographic growth (with greater animal exploitation in an attempt to cover food needs),

• By globalization (with an increase in the displacement of people, animals, and their derivatives),

• Due to the increase in occupational accidents (brucellosis, hepatitis, and tuberculosis, among others),

• Due to climate and ecological change (allows the adaptation of pathogens to new territories),

• Due to the tendency to adopt animals wild as pets, and the resistance of pathogens to the drugs used to combat them (by indiscriminate use) [21, 22, 23, 25, 26, 27].

In Latin America and the Caribbean, for example, there are 26 priority zoonotic diseases (Table 3).

Rabies; Leptospirosis; Brucellosis; Tuberculosis; Salmonella; Hydatidosis; Campylobacteria; Escherichia coli; Influenza; Chagas; Leishmaniosis; Venezuelan Equine Encephalitis; Trichinella spiralis; Hantavirus; Plague; Anthrax; Chikungunya; Equine Encephalitis; Dengue; Helminths; Food Borne Illness; Toxoplasmosis; Fasciolosis; Erysipelas; Burkholderia mallei; COVID-19

Table 3.

Zoonosis is considered priorities for health authorities in Latin America and the Caribbean.

Source: Drawn from Maxwell [28].

In the world, there are several zoonosis, considered emerging and priority among them are H5N1 and H1N1 influenza, SARS, and most recently Ebola and Zika [28]. Likewise, the stages through which zoonosis goes through to become pandemics are currently described (see Table 4).

Pre-emergence (Stage 1): The infectious agent is in its natural reservoir, but the alteration of the transmission dynamics due to environmental, ecological, social, and economic alterations allows: Expansion within the host population.; The spread to a new region.; It is transmitted to another non-host population.; That reaches the human being.; Large-scale agricultural or demographic changes, such as transport of livestock, to the region where the infectious agent has a niche or movement of wildlife to other regions in search of food, result in multidirectional transmission. For example, transmission like this can be between livestock and non-human primates and that can increase the probability that the pathogen reaches humans and spreads among different populations. Advance to the second stage??.; Localized emergency (Stage 2): The causative agent spreads from wildlife or livestock to people due to the slaughter of wild animals and from exposure to fomites in markets, on farms, or in the wild. It can affect small human groups orstepthen; become large outbreaks. They can be limited (for example, Ebola virus) or not (for example, Hendra virus); Full pandemic emergency (Stage 3): Transmission is already sustained from person to person and spread is on a large scale driven by global air travel (HIV/AIDS and severe acute respiratory syndrome, among others) and travel for reservoir and vector trade (West Nile virus). This stage depends on a long chain of transmission, so that it can occur, for this reason, pandemics in stage three are considered rare.

Table 4.

Stages in disease emergence.

Source: Modified from Stephen [29].

Strategies to try to predict potential pandemics are also described (Table 5).

Determining the relationship between the species of the pathogenic agent and the host. This is particularly important because the species closely related to each other favor the transmission of the etiological agent, that is, it passes easily from one host to another, however, in living beings human emerging pathogen species can come from closely related or distant hosts. The key to transmission to occur is contact.

The emergence of pathogens can be predicted based on the analysis of phylogenetic relationships. In this sense, it is known that wild pathogens that are more closely related to those that affect humans are more certain to infect people in contrast to those distant. Likewise, the analysis of the phylogenetic relationship allows for determining the pathogenesis.

The potential of emerging pathogens across a wide range of hosts (plasticity), thus, emerging pathogens have the ability to successfully transmit between different host taxa, thus increasing the probability of transmission to humans. Hence, the need for a constant study of these mechanisms in order to establish predictions.

The presence of factors that facilitate the passage of a pathogen between different host species (evolutionary capacity), although these aspects are little known, they are related to the ability to mutate. The understanding of these mechanisms facilitates the explanation of the high capacity for jumping between hosts that some species of pathogens have.; High transmission efficiency is often related to the ability of the pathogen to employ new transmission routes, hence, massive or generalized epidemic outbreaks are correlated with high transmission efficiency.

The prediction of ligand-receptor binding requires an understanding of the interactions involved between common elements (already existing) or new ones because the binding at the cellular level between the pathogen and the host cell is the initial and indispensable step (binding to the receptor is necessary but not sufficient condition to ensure infection since other factors are required) and it is usually associated with changes in the tropism of the host’s tissues. Despite the fact that there are many technological and scientific advances, only the cellular receptor of a little less than half of the pathogens that affect human beings is known. Highly species-specific receptors are considered as a barrier to infection between pathogens and unusual or new hosts.

The prediction of the transmissibility (virulence) of pathogens to humans is the greatest challenge to face in the study of pandemics since pathogen species that behave benignly in their natural hosts can trigger severe or lethal inflammatory responses in the host. New host coevolution patterns.

Table 5.

Prediction of pandemic potential.

Source: Modified from Stephen [29].

2.4 Theoretical and methodological interventions for zoonosis

Zoonosis is approached, studied, and intervened by classical or conventional epidemiology through the positivist paradigm that is based on the risk approach in the search for explanations about the health-disease process and about the circumstances that imply damage to human health and animal, due to the economic losses generated by the high figures of morbidity and mortality attributed to zoonotic transmission diseases, which undoubtedly hinder the development of countries [10, 30].

The advances and contributions achieved with the methods and theories of classical epidemiology are great and important, however, for the management of zoonoses, an integral vision is required that allows understanding of the complexity of the relationship between animals and human beings due to ecosystem and intervening social variables since it is necessary to go beyond the mere identification of infectious agents, pathogenesis, transmission, control, and treatment, in this sense, the paradigms of complexity and chaos have been used for the study of zoonosis [30, 31, 32, 33, 34].

The single and multi-causality approaches to risk are not enough to understand and explain the complex interactions that occur in zoonosis, paradigms are required that go beyond system theories, structural functionalism, the inability to control the pathogenic agent, the articulation of the epidemiological discourse to health policies, the ecosystem approach and the social component (behavior and culture in the relationship between equals, social determinants, and inequities in health), in this sense, a holistic approach to zoonoses (prevents the fragmentation and decontextualization of the health problem by considering it broad and complex) [30, 35, 36, 37, 38, 39, 40, 41].

Hence, international health organizations issue general and comprehensive recommendations that contribute to adequate surveillance and response capacity in the event of the emergency and re-emergence of zoonosis (see Table 6).

Recommendations

Generation of sufficient financial resources that are sustainable over time. Multisectoral coordination, fundamentally between animal and human health and the ecological field, all action for the control or eradication of zoonosis must be coordinated. Approach strategies adapted to local conditions. Introduction of information and communication technologies in order to facilitate the exchange of information between the different sectors and favor the analysis of zoonosis situations and the health management of the problem. Adaptation or design of programs for the control of zoonosis based on the scientific knowledge that is constantly produced on the subject. Training of health personnel with a multidisciplinary approach for the prevention, diagnosis, and treatment of these diseases. Create a network of laboratories for the diagnosis of international zoonosis. Promote the participation of the social sciences in addressing zoonosis. Surveillance of zoonosis is everyone’s task. Frontal and direct fight against the practices and behaviors that contribute to the genesis and maintenance of zoonosis as endemic. Community participation in decision-making regarding their health and quality of life is essential. Promote the idea that zoonosis is a problem for everyone, for countries with low, medium, and high economic income.

Table 6.

Recommendations for comprehensive surveillance and adequate response to zoonosis.

Source: Ministry of Health [42].

These recommendations seek to prevent, monitor, and control zoonosis to reduce its impact on health, but to achieve this, the joint participation of animal health, human health, and the environmental sector are required.

3. Conclusions

This writing constitutes a brief but concise compendium on zoonosis that starts from the meaning of the word, goes through its general aspects, through the epidemiological panorama, and finally through the theoretical and methodological interventions that it has been the object of, it can then serve as a tool for health professionals and for the community in general in acquiring knowledge about zoonosis or for updating them in the fight against these diseases because with the information it offers, the dynamics of the factors that condition or determine their emergence can be understood, re-emergence, prevalence, and distribution in the animal and human population.

However, in the field of health control of zoonosis and from what is stated in this paper, it is concluded that the approach to zoonosis requires cross-cutting, multidisciplinary, and inter-institutional health care, in addition to the incorporation of social, cultural, and economic concepts that define the animal-man relationship, as well as the consideration of the circumstances that imply the involuntary contact between both actors (often ignored) as a result of mutual coexistence and the incorporation in the epidemiological surveillance of diseases of this type that have a low frequency of appearance.