Did you know?
- There are over 200 known types of zoonoses in the world.
- Zoonoses comprise an enormous percentage of new and existing diseases in animals and humans.
- Zoonoses, like rabies, are 100% preventable through vaccination and other methods
- Diseases such as HIV, began as a zoonosis but later mutated into human-only strains
- Zoonoses can cause recurring disease outbreaks, such as Ebola virus disease, salmonellosis and the novel coronavirus that causes Covid-19.
What are Zoonoses?
Zoonoses (singular; Zoonosis) or zoonotic diseases are the “diseases and infections that are naturally transmitted between vertebrate animals and man”. This is as defined in 1951 by the World Health Organization (WHO) Expert Committee on Zoonoses.
The term ‘zoonosis’ is considered to be shorter and more convenient than ‘anthropozoonosis’ (animals to humans) and ‘zooanthroponosis’ (humans to animals), which are terms based on the prevailing direction of transmission between humans and other vertebrates.
Zoonosis can be caused by bacteria, viruses, fungi and parasites. Some examples of each include:
- Bacteria: salmonellosis, bovine tuberculosis, anthrax, psittacosis, brucellosis etc.
- Viruses: rabies, Ebola, covid-19, avian influenza, West Nile virus etc.
- Fungi: dermatophytosis, sporotrichosis, histoplasmosis etc.
- Parasites: include cryptosporidiosis, trichinellosis etc.
Animals play an essential role in maintaining zoonotic infections in nature.
A brief review of some cases of zoonotic disease outbreak
Ebola is an uncommon, however extremely fatal, disease caused by infection with one of five strains of Ebola virus. It is highly infectious and exposure to the virus most frequently occur through direct contact with the blood or bodily fluids of an infected patient, direct contact with bats or by handling contaminated meat from wild animals. It can also occur through indirect contact with an infected patient’s items, such as bed sheets, syringes, or clothes.
The first outbreak of Ebola was in 1976 near the Ebola River in the Democratic Republic of the Congo. Since then, episodic outbreaks continued to transpire all over Africa.
On March 23, 2014, the World Health Organization (WHO) reported the first cases of EVD in West Africa in what would become the largest Ebola virus epidemic in history. Over two years, a total of 28,616 cases of EVD and 11,310 deaths were reported in Guinea, Liberia, and Sierra Leone. An additional 36 cases and 15 deaths occurred when the outbreak spread outside these three countries.
H5N1 is a vastly pathogenic strain of avian influenza virus and it originated among domestic poultry stocks in Asia and the Middle East. Outbreaks of H5N1 began in the 1990s, and the H5N1 strain was isolated in 1996 from a goose in China. H5N1 avian flu is highly contagious and deadly in birds, the virus spread rapidly throughout Asia.
Even though human infection with H5N1 is erratic, people can contact avian flu after direct contact with infected birds. The first human cases were reported in Hong Kong in 1997. Since 2003, over 650 cases of human infection with H5N1 have been reported in over 15 countries.
Scientists’ fear that a mutated form of H5N1 may arise that is contagious in humans and can be spread through sneezing or coughing, leading to the possibility of a worldwide epidemic.
The first case of Lassa fever globally was identified in Lassa, a settlement in Borno State, North East Nigeria in 1969. It has emerged as a severe outbreak of public health threat and burden in Nigeria in the recent past. As revealed in a publication titled Re-emerging Lassa fever outbreaks in Nigeria: Re-enforcing One health community surveillance and emergency response practice, “Nigeria is currently experiencing a smoldering Lassa fever outbreak in almost 20 states. 175 confirmed and suspected cases and 101 deaths since August 2015 have been reported”.
The Lassa virus is transmitted by rodents and poses potential disease ecology and public health impact. It is spread by contact with infected rodent’s feces, urine, inhaling contaminated dust, eating contaminated food, or by contact with the fluids of an infected person dead or alive.
How do Zoonoses spread?
There is often close contact between people and animals. Hence, it is important to be aware of the common ways people can get infected with germs that can cause zoonotic diseases.
Zoonotic diseases can be transferred from animals to humans in several different ways, including:
- Direct contact
Direct contact is one potent means by which zoonotic diseases spread. It involves contact with the bodily fluids of an infected animal, such as saliva, blood, urine, mucus, or feces etc. This can happen as a result of bite or scratch by an infected animal or by merely touching or petting one.
- Indirect contact
Indirect contact involves coming in contact with an area where infected animals live or roam, or by touching surfaces or objects (fomites) that have been contaminated with germs. Such areas include; aquarium tanks, chicken coops, cages, or kennels.
A vector is a living organism that actively transmits a disease-causing organism. Examples are; mosquitoes, ticks, fleas, lice. The vector will bite the infected animal and then bite a human, thereby passing on the zoonotic disease.
- Food-borne and water-borne
Zoonosis can come from contaminated water sources, animal food products, improper food handling, or inadequate cooking. Sources of infection include; unpasteurized milk, undercooked meat or eggs, raw fruits, vegetables or water contaminated with infected faeces.
Who is at a higher risk of zoonotic diseases?
Farmers, abattoir workers, zoo or pet shop workers, and veterinarians have an increased risk of being bare to zoonotic diseases. They can also become carriers and pass those diseases on to other people.
Prevention and control
People come into contact with animals all the time, but there are several steps each person can take to help prevent infection. These include:
- Keeping hands clean: Washing hands with clean soap and running water after being around animals, even if not touching them, can stop germs spreading.
- Choosing a pet wisely: Thoroughly researching types of pets and taking steps to be safe around them can help prevent disease.
- Making sure pets are under care of veterinarians to help protect pets and families from possible zoonotic infections
- Handling food safely: A person can prevent infections, such as salmonella, by ensuring food is cooked properly, that food preparation areas are clean, and by washing dishes and pots after use
- Researching diseases before travel: Being aware of the different types of zoonotic diseases when traveling and taking precautionary steps with vaccines are essential.
Collaborations across sectors relevant to zoonotic diseases, particularly among animal and human health disciplines, are essential for mitigating the impact of endemic and emerging zoonotic diseases of public health importance. Appropriate structures must be in place before an outbreak, epidemic or pandemic occurs to have an effective, coordinated public- and animal-health response.
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- B.B.Chomel;Encyclopedia of Microbiology https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7149995/
- Centers for Disease Control and Prevention (CDC); https://www.cdc.gov/onehealth/basics/zoonotic-diseases.html
- Healthline; https://www.healthline.com/health/zoonosis
- Seymour on January 15, 2018; https://www.medicalnewstoday.com/articles/320618#prevention
- World Health Organization (WHO); https://www.who.int/news-room/fact-sheets/detail/zoonoses
- Nationwide Children’s Hospital HH-I-372 https://www.nationwidechildrens.org/conditions/zoonoses
- World Health Organization (WHO); avian influenza update20141204.pdf
- L.-F. Wang, G. Crameri “Emerging zoonotic viral diseases” Rev. sci. tech. Off. int. Epiz., 2014