ZOONOTIC INFECTIONS

The phrase Zoonosis’ is a Greek word that comes from zoon (which means animal) and osis (which means ill). Zoonoses (plural: zoonosis) therefore, are animal diseases transmissible to humans. Zoonotic infections which can also be called zoonosis are diseases/infections caused by pathogens that can be passed or shared between humans and animals (Table 1). They are diseases that are transmitted from wild or domestic animals to humans. Several human diseases including but not limited to Ebola, lassa fever, epidemic typhus, Lyme disease, severe acute respiratory syndrome (SARS) and anthrax have their origin from animals (that serves as reservoir hosts for the causative agents of these pathogens). And these zoonotic infections are mostly common amongst animal tenders, farmers and people who work with or live close to animal farms where these animals are reared. Infections transmitted from humans to animals are called anthroponotic disease or anthroponosis. Human invasion or encroachment into the wildlife areas and forests areas where humans rarely live have seen us experiencing more epidemic outbreaks of zoonotic infections around the world. The continued distribution of disease-causing microorganisms in the animal populations is a menace to the total wellbeing of the human population. Humans depend on these animals for meat, and they also use them as their pets. A constant attachment to these animals can serve as a route via which most zoonotic infections reach susceptible human hosts.

The long interaction of man with animals coupled with the domestication of these animals over time has increased the frequency of zoonosis in the human population. Animals produce respiratory secretions, sputum (or saliva) and exudates from wounds and these are highly contagious fluids that directly infect humans and cause a variety of diseases. The animals that are the likely source of transmitting zoonotic infections can either be farm animals (e.g. cow, birds, goats, swine, cats and dogs) or wild animals (e.g. monkeys, squirrels, raccoons, mice, and rats). It is noteworthy that animals play a critical responsibility in the continual maintenance of infectious diseases in the environment – as the pathogens causing these diseases are usually nurtured in animals until they infect a susceptible human being (who becomes infected by chance). Individuals that are usually at risks of contracting a zoonosis include infants, the elderly, AIDS patients, cancer patients and those who have continual unprotected contact with either wild or domestic animals. Zoonotic infections are different from anthroponosis – which are infectious diseases whose pathogen are usually maintained in a human reservoir and which can be contracted by susceptible human or animal hosts.

Table 1. Some common zoonotic infections and their animal reservoirs

MICROORGANISMINFECTIONANIMAL HOST
Bacterial zoonotic infectionsSalmonellosis Plague Cat scratch disease Encephalitis Lyme disease Campylobacteriosis Mycobacterium  Anthrax Psittacosis Tularemia Brucellosis          Rodents, Rat, and Birds
Viral zoonotic infectionsEbola virus disease (EVD) Lassa fever Severe acute respiratory syndrome (SARS) Rabies Hantavirus Avian influenza Cowpox West Nile fever Bovine Spongiform- Encephalopathy (BSE)      Rodents, Chimpanzees, Monkeys, Rats (Mastomys natalensis for Lassa fever), Dogs, and Birds
Parasitic (protozoan) zoonotic infectionsToxoplasmosis Giardiasis Malaria Balantidiasis  Tapeworms    Arthropods (insects)
Fungal (mycotic) zoonotic infectionsDermatophytosis Cryptococcosis Cryptosporidiosis Histoplasmosis Ringworm 
Helminthic zoonotic infectionsAscariasis Strongyloidiasis Trichinosis   

FURTHER READING

Aschengrau A and Seage G.R (2013). Essentials of Epidemiology in Public Health. Third edition. Jones and Bartleh Learning,

Gordis L (2013). Epidemiology. Fifth edition. Saunders Publishers, USA.

Nelson K.E and Williams C (2013). Infectious Disease Epidemiology: Theory and Practice. Third edition. Jones and Bartleh Learning. 

Riedel S (2004). Biological warfare and bioterrorism: a historical overview. BUMC Proceedings, 17:400-406. 

Rothman K.J, Greenland S and Lash T.L (2011). Modern Epidemiology. Third edition. Lippincott Williams and Wilkins, Philadelphia, PA, USA.

Schneider M.J (2011). Introduction to Public Health. Third edition. Jones and Bartlett Publishers, Sudbury, Massachusetts, USA.

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