Zoonotic Microorganisms and their Pathological Impact on Human Health

Ranno Sisto^*
*Correspondence: Ranno Sisto, Department of Microbiology and Parasitology, University of São Paulo, São Paulo, Brazil, Email:

Introduction

Zoonotic diseases-those that are transmitted from animals to humans-have shaped human history and continue to pose significant public health threats across the globe. The causative agents of these diseases, known as zoonotic microorganisms, encompass a wide array of pathogens including bacteria, viruses, fungi, protozoa, and helminths. As human interactions with wildlife, domestic animals, and natural ecosystems intensify due to urbanization, deforestation, globalization, and climate change, the likelihood of zoonotic spillover events has increased dramatically. Notable pandemics and epidemics-such as the 1918 influenza pandemic, HIV/AIDS, SARS, Ebola, avian influenza, MERS, and the recent COVID-19 pandemic-have all been linked to zoonotic origins. Beyond pandemics, endemic zoonotic infections like rabies, leptospirosis, brucellosis, and tuberculosis continue to exert a heavy burden, especially in low- and middle-income countries [1,2].

Description

Bacterial zoonoses are among the most widespread and impactful of all zoonotic infections. Many are vector-borne or transmitted through direct animal contact, contaminated food, water, or aerosols. These facultative intracellular pathogens cause brucellosis, a disease transmitted through unpasteurized dairy products or direct contact with infected livestock. Brucellosis is characterized by undulant fever, malaise, arthritis, and potential complications like endocarditis. The bacteria invade macrophages and evade immune responses via type IV secretion systems. A close relative of Mycobacterium tuberculosis, M. bovis causes zoonotic tuberculosis, primarily transmitted via inhalation or ingestion of contaminated dairy products. It can mimic pulmonary TB and also cause extrapulmonary disease, especially in immunocompromised individuals. This spirochete causes leptospirosis, a re-emerging disease transmitted through contact with water contaminated by urine from infected animals. The pathogen can lead to jaundice, renal failure, hemorrhage, and meningitis [3].

Avian and swine influenza strains can reassort in animal hosts and cross the species barrier to infect humans, sometimes with deadly consequences. The 2009 H1N1 pandemic and avian H5N1/H7N9 outbreaks underscore the importance of surveillance in animal populations. A neurotropic virus transmitted through the saliva of infected mammals (commonly dogs, bats, raccoons), rabies causes progressive encephalitis that is nearly always fatal once clinical signs appear. Prompt post-exposure prophylaxis is life-saving. Ebola virus and Marburg virus are highly lethal pathogens believed to originate from bats. These viruses cause hemorrhagic fever with high case fatality rates, multi-organ dysfunction, and widespread endothelial damage. Transmitted via rodent urine or droppings, hantaviruses can cause hantavirus pulmonary syndrome or hemorrhagic fever with renal syndrome. An emerging paramyxovirus from fruit bats, Nipah causes severe encephalitis and has zoonotic transmission through pigs or contaminated fruit [4]. Risk factors include agricultural occupations, bushmeat consumption, deforestation, exotic pet ownership, poor sanitation, climate change, and global travel. Urbanization brings humans closer to animal reservoirs, facilitating spillovers. Climate change also affects vector distributions and wildlife behavior, altering disease patterns [5].

Conclusion

Zoonotic microorganisms represent a profound and multifaceted threat to human health, capable of sparking global pandemics, overwhelming health systems, and destabilizing societies. They encompass a wide spectrum of pathogens-bacteria, viruses, fungi, protozoa, and helminths-with diverse routes of transmission and pathological consequences. Whether through respiratory failure, neurological compromise, chronic organ dysfunction, or systemic inflammation, zoonotic pathogens can cause significant morbidity and mortality. As human activities increasingly encroach upon natural ecosystems and disrupt animal populations, the risk of zoonotic spillovers grows. Addressing this challenge requires a holistic, interdisciplinary, and globally coordinated approach-the One Health framework. By integrating veterinary science, human medicine, ecology, and public health, we can better anticipate, prevent, and respond to zoonotic threats. Continued research, education, surveillance, and investment in infrastructure are essential to mitigate the impact of zoonotic diseases and safeguard the health of humans, animals, and the planet alike.

Acknowledgement

None.

Conflict of Interest

None.

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