What are Zoonoses?
Zoonoses are diseases that can be transmitted from animals to humans through bites, scratches, or consumption, resulting from bacterial, viral, parasitic, or fungal infections in animal hosts. These diseases have placed their mark on human history, and influenced the (re)development of societies, and governments. Technologies, and practices relating to human, animal and planetary issues have drastically changed to conform with infection prevention and control of zoonotic diseases.
Brief History of Zoonoses
Emergence of zoonotic diseases can be traced from the domestication of animals.
The first epidemic was the Justinian Plague, and this began in the middle of the 6th century in the Byzantine Empire. Over a 200-year period, it is thought that nearly 25 million people died of the plague.
The second epidemic, referred to as the Great Plague or the Black Death, occurred during the 14th century. The Great Plague began in China and traveled by established trade routes through-out Asia and Europe. It ultimately killed millions of people and wiped out 60% of Europe’s population.
The third plague, also known as the Modern Plague, began in China in the late 19th century and eventually killed 10 million people worldwide. Rat-infested shipping containers and merchant ships, along with rat fleas, are considered to be likely reasons for the spread of the plague.
These diseases were believed to have been caused by zoonotic bacteria, usually found in small mammals and their fleas. It was transmitted between animals through fleas.
Zoonoses have different transmission modes including:
- Direct zoonosis: The disease is directly transmitted from non-humans to humans through media such as air (influenza) or through bites and saliva (rabies).
- Indirect Zoonosis: In contrast to direct zoonosis, transmission can also occur via an intermediate species (referred to as a vector), which carry the disease pathogen without getting sick. Mosquitoes and Tsetse flies are vectors incriminated in the transmission of Dengue and Sleeping Sickness( African Trypanosomiasis)
- Reverse zoonosis (otherwise known as anthroponosis): This is what occurs when humans infect non-humans [spillbacks]. There have been some reports of pet owners transmitting diseases to their pets, especially cats and dogs.
Recently, there has been a rise in the incidence of zoonotic diseases which could be attributed to:
1. Climate Change: There is a strong link between climate change and the epidemic emergence in the last two decades. Climate change caused mass migration of species to new areas. This consequently brought about contact with native species that wouldn’t normally interact with these alien species. The significant change in climatic conditions has led to vector proliferation. A typical scenario is the growing cases of Neglected Tropical Diseases (NTDs) such as onchocerciasis and lymphatic filariasis in which vectors such as the black flies and mosquitoes are favored by the variabilities of climate.
2. Pets: The increasing rate of pet owners contribute to the rising cases of zoonotic diseases. Dogs and cats are transmitters of so many zoonotic diseases such as rabies and toxoplasmosis. Pets may also serve as reservoirs of viral diseases.
3. Animal attacks and wildlife market: The wildlife trade may increase the risk of contracting zoonosis. This is so because it directly increases the number of interspecies interactions seeing that most of these animals are carriers of disease agents.
4. Arthropods (Insect Vectors): Vectors such as those that belong to the family Culicidae, Simulidae, Muscidae, Glossinidae, etc., have been pointed to in the transmission of zoonotic diseases. The surge in the prevalence of the diseases they transmit is a reflection of how most of the aforementioned factors have favored the growth of the vectors.
5. Farming: Contact with farm animals can lead to disease in farmers or others that come into contact with infected farm animals. For example, farmers can contract the following diseases:
- Avian Influenza (poultry workers at risk of being infected)
- Glanders (those who work with Equine (horses and donkeys) are at risk of being infected)
- Listeriosis, Chlamydia and Q-Fever (sheep and goat farmers are at risk of being infected)
- Brucellosis, Anthrax etc. (cattle/dairy farmers at risk of being infected)
- African Swine Fever (swine farmers are at risk of being infected)
Note: Veterinarians and other animal health workers are exposed to unique occupational hazards when it comes to zoonotic diseases
6. Hunting: Hunting is the human practice of seeking, pursuing, capturing, or killing wildlife or feral animals. Hunting has long been a part of human culture and has been practiced for various reasons, including the procurement of food and trade. However, hunting can also increase the risk of zoonotic diseases. When humans hunt wild animals, they come into close contact with them and their bodily fluids, which can contain disease-causing pathogens. If the animal is infected with a zoonotic disease, there is a risk of transmission to the hunter or anyone who handles the animal’s body.
One Health’s Vantage Point on Zoonoses
As the name implies, One Health is an approach that recognizes that the health of people is closely connected to the health of animals and our shared environment. One health concept represents a more holistic approach to preventing disease for the benefit of humans and their domesticated animals by preventing outbreaks of zoonotic disease in animals and people, improving food safety and security, reducing antimicrobial resistant infections and improving human and animal health.
One of the main goals of One Health still remains reassessing the current animal disease information system, and adjusting it to prevailing surveillance requirements. Work being done saw that in July, 2017 the One Health Zoonotic Prioritization Workshop was initiated by the Nigeria Centre for Disease Control (NCDC) and the Federal Ministry of Agriculture and Rural Development’s Department of Veterinary and Pest Control Services. This workshop was supported by the Africa Field Epidemiology Network (AFENET), Global Implementation Solution (GIS), US Centers for Disease Control and Prevention (CDC) and the Zoonotic Disease Unit (ZDU) of Kenya.
The primary objectives of the prioritization process were: to identify priority zoonotic diseases in Nigeria, and to strengthen surveillance of communicable diseases systems in the human health sector in accordance with World Health Organization standards.
To sum it up, it is important to note that One Health serves as a link between animal health and public health agencies. At least 61% of all human pathogens are zoonotic, and have represented 75% of all emerging pathogens during the past decades. Prevention activities for pandemics have shown the possibility that a common interdisciplinary approach can and should be used. This is not only true for a particular disease, but also more widely on all zoonoses. Therefore, a One Health approach can achieve the best health outcomes for people, animals, and plants in a shared environment by protecting global health security, biodiversity and conservation and by promoting collaboration across all sectors.