Across the world today man has been awakened with a new trend in the spread of disease from animals to man. Man and animals are supposed to cohabit in their natural habitat as a means of balance in nature, however, today many modern diseases started out as zoonotic disease. But, what could have been responsible for this trend? Is it that animals are now transmitting diseases to humans or has man in its activities tampered with nature?
Zoonosis is an infection acquired by man from animals as a result of man’s interaction with these animals. Zoonotic diseases could range from minor short term illness to a major life threatening illness, some can even cause death. Recall the case of Ebola virus in July, 2014 which was also recorded in Nigeria and its origin traced to fruit bats.Other examples of zoonotic diseases are: bird flu, rabies, zika fever, lassa fever, tuberculosis etc.
It is estimated that about one billion illnesses and millions of deaths globally occur every year due to zoonoses (source; WHO). It has gained global attention owing to its ability to spread internationally due to global networks and rapid increase in trade amongst nations.
The recent covid-19 pandemic around the world has been suspiciously linked to bats and the world health stakeholders are still in the search for a vaccine to curb its spread and stop the daily rate of increasing cases.
PATHOGEN RESPONSIBLE FOR ZOONOSIS IN MAN
Pathogens are disease producing agents or you can refer to them as causative agents of diseases. The pathogens responsible for the spread of zoonoses are:
Virus: Viruses are the smallest of all the pathogens. They are special because they are only alive when they get inside the cell of a living organism.Examples of virus zoonotic diseases are Bird flu, Ebola virus disease, Influenza, Lassa fever, Coronaviruses such as Severe Acute Respiratory Syndrome (SARS-Cov), Middle East Respiratory Syndrome(MERS- Cov), etc.
Bacteria: Bacteria aremicroscopic, single celled organisms that can survive in diverse environments. Examples of bacteria zoonotic diseases are Tuberculosis, Anthrax, Bartonella (cat scratch fever), Lyme disease, Leptospirosis, etc.
Fungus: Fungal can be single celled or complex multicellular organisms. Fungal diseases can be found in any habitat but most of them are present on land. Examples of fungal zoonotic diseases are Dermatophytosis, Coccidioidomycosis, Histoplasmosis, etc.
Parasites: Parasites are living organisms that reside on or within another living organism, called its host. Zoonotic diseases that are caused by parasites have different symptoms depending on the parasite and the individual involved.Examples of parasitic zoonosis infections are African sleeping sickness, Echinococcosis, Toxocariasisetc.
Example of Some Selected Zoonotic Diseases and the Animal Associated With Its Spread
RABIES: Rabies is a disease caused by a virus called Rabies virus. It affects the nervous system of mammals. It is typically spread through bites and scratches from infected animals like dogs, bats, wolves and foxes etc. rabies infection can be prevented through vaccination.
HUMAN IMMUNODEFICIENCY VIRUS (HIV): HIV used to be a zoonotic disease transmitted to humans in the early part of the 20th century, though; it is now mutated to a separate human only disease. It is believed to have originated from non-human primates.
BIRD FLU: Bird flu disease is caused by Influenza A virus (H5N1), which is transmitted through closed contact with infected wild birds and domestic birds (chicken).
BARTONELLA (Cat Scratch Disease): Cat scratched disease is caused by a pathogen called Bartonellahenselae, it is transmitted through bites and scratches from infected cats.
EBOLA VIRUS DISEASE: Ebola disease is caused by a virus called Ebola virus spp, it is transmitted by fruits bats, chimpanzees, gorillas, monkeys etc. through contact with their body fluids and organs.
LASSA FEVER: Lassa fever is caused by Lassa fever virus, it is transmitted through exposure to infected rodents like rats, mice etc.
ECHINOCOCCOSIS: Echinococcosis disease is caused by Echinococcosis spp,it is transmitted by dogs, foxes, wolves etc. through ingestion of the infected eggs either through food or water.
MIDDLE EAST RESPIRATORY SYNDROME (MERS): Middle East Respiratory Syndrome (MERS) is caused by MERS coronavirus. Transmission is through close contact with infected bats and camels.
SEVERE ACUTE RESPIRATORY SYNDROME (SARS): Severe acute respiratory syndrome is caused by SARS coronavirus. SARS transmission is through close contact with the respiratory droplets of infected bats and civets.
TUBERCULOSIS: Tuberculosis is caused by Mycobacterium bovis. It is transmitted by infected cattle, pigs, domestic cats and wild carnivores through the milk, exhaled air, sputum, urine, faeces and pus from the infected animal.
ZIKA FEVER: Zika fever is caused by Zika virus which resides in chimpanzees, gorillas, monkeys and baboons. It is transmitted through mosquito’s bites, sexual intercourse, and blood transfusion and also through bites from infected animals.
NIPAH VIRUS INFECTION: Nipah virus infection is caused by Nipah virus; its transmission is through close contact with infected bats and pigs.
HANTAVIRUS: Hantavirus is caused by Hantavirus spp. It is transmitted through exposure to faeces, urine, saliva or bodily fluids of infected deers, mice, cotton rats etc.
ANTHRAX: Anthrax is a bacterial zoonotic infection caused by Bacillus anthracis. Animals associated with anthrax spread are herbivores such as cattle, goats, sheep, etc. it is transmitted through ingestion or inhalation of spores or through close contact with the spores.
LYME DISEASE: Lyme disease is a bacterial zoonotic infection caused by Borreliaburgdorferi. Animals such as wolves, dogs, birds, rodents, reptiles etc. have been associated with it. The transmission to humans is through a tick bite.
TOXOCARIASIS: Toxocariasis is caused by Toxocaracanis or Toxocaracati. Toxocariasis is transmitted from dogs, cats, foxes etc. to man when a man eats unwashed vegetables, under-cooked meat or ingestion of eggs in soil.
HISTOPLASMOSIS: Histoplasmosis is caused by a fungus Histoplasma Capsulatum. Animals such as birds and bats are associated with it. Transmission is through inhaling of the fungi.
LEPTOSPIROSIS: Leptospirosis is caused by a bacteria caused by Leptospirainterrogans. Rats, goats, cattles, buffallos, foxes, dogs etc. have been associated with it. The means of transmission to man is through direct or indirect contact with the urine of infected animals.
AFRICAN SLEEPING SICKNESS: African sleeping sickness is caused by a parasite called Trypanosoma brucei rhodesiense. It is transmitted by tsetse fly from wild animals or domestic animals to man through a blood suck process.
The list of zoonotic diseases goes on and on, the above diseases are just a few selected ones from the disease caused by animals.
Animals serve as companions, source of entertainment, security purpose and source of food to man among much other importance. Hence, man and its animals are inseparable. But, adequate care must be taken whenever we interact with these animals. Most of these zoonotic diseases have come to stay and man cannot deny its existence. But, we can always win the fight against zoonotic diseases by playing our part through safe hygiene practices around animals and ensure our pets are also properly vaccinated.
Watch out for the second series on zoonosis where we will consider how to prevent zoonotic disease, until then happy reading.
Oluwafemi Abidemi Amos is a graduate of Zoology with great passion for Public Health Entomology and Parasitology who find it interesting to enlighten the public with the right and correct health information and to contribute to the research and knowledge base of the society on a global state in areas such as Neglected Tropical Diseases (NTDs), Entomologically related diseases, and Parasitology. He is also the founder of Great Mind Tutors (GMT) whose focus is to bring out the genius in every child and a team member of Career Builder Network (CBN) with vision to help student achieve excellence in academics and life.