Zoonotic diseases are very common, both in the United States and around the world. Scientists estimate that more than 6 out of every 10 known infectious diseases in people can be spread from animals, and 3 out of every 4 new or emerging infectious diseases in people come from animals. Because of this, CDC works 24/7 to protect people from zoonotic diseases in the United States and around the world.
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Anyone can get sick from a zoonotic disease, including healthy people. However, some people are more at risk than others and should take steps to protect themselves or family members. These people are more likely than others to get really sick, and even die, from infection with certain diseases. These groups of people include:
People can come in contact with animals in many places. This includes at home and away from home, in places like petting zoos, fairs, schools, stores, and parks. Insects, like mosquitoes and fleas, and ticks bite people and animals day and night. Thankfully, there are things you can do to protect yourself and your family from zoonotic diseases.
Prevention methods for zoonotic diseases differ for each pathogen; however, several practices are recognized as effective in reducing risk at the community and personal levels. Safe and appropriate guidelines for animal care in the agricultural sector help to reduce the potential for foodborne zoonotic disease outbreaks through foods such as meat, eggs, dairy or even some vegetables. Standards for clean drinking water and waste removal, as well as protections for surface water in the natural environment, are also important and effective. Education campaigns to promote handwashing after contact with animals and other behavioural adjustments can reduce community spread of zoonotic diseases when they occur.
Both Gram-negative and Gram-positive bacteria are capable of inducing zoonoses. Based on etiology, bacteria account for most zoonotic diseases. It has been estimated that among the zoonotic pathogens originating from bovine origins, about 42% are of bacterial origin, 22% viral, 29% parasitic, 5% fungal, and 2% prion origin [9]. Similarly, both DNA and RNA viruses are known to be responsible for zoonoses; however, compared to DNA, the RNA viruses are more frequently linked with zoonoses [10].
Pathogens can be transmitted to humans directly or indirectly from animals. Diseases that are transmitted directly to humans from animals through media such as air are known as direct zoonoses [11]. One classical example of direct zoonoses is avian influenza, which is a viral disease that spreads from animals to humans through droplets or fomites. Infected animals can also directly transfer pathogens to susceptible humans by bites such as in the case of rabies, which is one of the deadliest zoonotic diseases. It is caused by a rabies virus that belongs to Rhabdoviridae. When a rabid animal (dog, bat, monkey, skunk, raccoon, or fox) bites a human, the virus directly enters the human body through saliva. Similarly, pathogens can be transmitted to human via vectors (Dengue fever). Arthropods like mosquitoes and ticks are often considered to be the only vectors; however, any animal that has the potential to transmit pathogens to human can be considered a vector [12].
Depending on the ecosystem in which pathogens circulate, zoonotic diseases are classified into several categories. For example, some zoonoses are classified into synanthropic zoonoses and exoanthropic zoonoses. Synanthropic zoonoses have an urban (domestic) cycle in domestic and synanthropic animals such as with urban rabies and zoonotic ringworm. Exoanthropic zoonoses are usually accompanied by a sylvatic (feral and wild) cycle in natural foci outside human habitats such as with arboviroses, wildlife rabies, and Lyme disease [13]. However, some zoonoses can also circulate in both urban and natural cycles such as yellow fever, Chagas disease, and dengue fever. In addition, there are some other zoonotic diseases that can be transmitted by arthropods, food, rodents, and some are waterborne [14].
Cattle, sheep, goats, dogs, cats, horses, pigs, and other domestic animals act as reservoirs of pathogens of domestic zoonoses and can transmit the diseases to humans [26]. Pathogens can be transmitted through direct contact or animal origin foods. Examples of zoonotic diseases that can be transmitted to humans from domestic animals include anthrax, rabies, tuberculosis, brucellosis, campylobacteriosis, leptospirosis, toxoplasmosis, balantidiasis, ancylostomiasis, toxocariasis, listeriosis, bovine pustular stomatitis, rotavirus infection, and Q fever [10,26,27].
A variety of infectious diseases (viral, bacterial, parasitic, and fungal) are associated with pets and companion animals [50]. The zoonotic diseases frequently associated with pets and companion animal include brucellosis, campylobacteriosis, chlamydiosis, catch scratch fever (Bartonella henselae), ehrlichiosis, giardiasis, hantavirus, hookworms, influenza, rabies, Lyme disease, rocky mountain spotted fever, leptospirosis, monkey pox, pasteurellosis, Q fever, plague, roundworms, salmonellosis, staphylococcosis (MRSA), streptococcosis, toxoplasmosis, and tularemia [50,51,52]. Many types of zoonoses such as salmonellosis, staphylococcosis, and rabies are found in a wide range of pets and companion animals.
Nowadays, birds like canaries, finches, sparrows, parrots, parakeets, budgerigars are very common in the developed and developing countries [53]. Like pet animals, these game and ornamental birds are also potential transmitters of zoonotic diseases like Coxiella burnetii, Coxiella psittaci, Salmonella spp., Listeria monocytogenes, Erysipelothrix rhusiopathiae, Mycobacterium spp., Lyme disease, and transmitters of different viruses like fowl pox virus and Newcastle disease virus [54]. Many of these pathogens are potentially enough to cause serious diseases in human such as salmonellosis, chlamydiosis, and avian influenza A H5N1 [53]. In addition, there are wide varieties of other bacterial zoonoses in game and ornamental birds including Pasteurella spp., Klebsiella spp., Yersinia spp., Pseudomonas spp., Staphylococcus aureus and E. coli [55,56,57]. In fact, there is evidence of Escherichia coli O157:H7 (enterohaemorrhagic) transmission to human through food of animals that originally came from wild passerines (such as European starlings) [58].
Increased human-animal contact or interaction resulting from changes in human and animal behavior, habitat, ecology, vector biology, pathogen adaptability, change in farm practices, livestock production systems, food safety, urbanization, deforestation, and climate change are among the triggering factors for emergence of zoonotic diseases [121]. Wildlife can act as a source or a reservoir for emerging and remerging zoonotic disease-pathogens [122].
Emerging and re-emerging diseases have significant impacts, not only on public health, but also on socio-economic issues around the globe [123,124,125,126]. Among 175 reported emerging diseases, 132 diseases are considered to be emerging zoonotic diseases [5]. Another report estimated that about 60.3% of the emerging diseases can be categorized under zoonoses. Among them, 71.8% originated from wildlife [127].
Wild animals such as mammals, reptiles, birds, fish, and amphibians act as a reservoir of zoonotic pathogens with the potential of transmission to humans or other animal hosts. The involvement of wild animals in the epidemiology and transmission of zoonotic diseases is alarming. The transmission patterns of wildlife zoonoses are influenced by the nature of pathogen involved and climatic parameters such as temperature, humidity, and rain fall [122]. The emergence and re-emergence of these pathogens is dependent on their transmission patterns among wild animals, domestic animals, and humans. Factors impacting these processes include (1) rapid increase of the human population; (2) ease of local and global travel; (3) increased human exposure to animals and animal products; (4) wildlife farming; (5) hunting, handling, and transporting wildlife (including carcasses) with limited precautions; (6) consumption of wild meat (such as bush meat); and (7) differences in agricultural practices [123,148,149].
Animal deaths caused by zoonotic diseases can impose massive economic losses on the livestock sector of any country. Even if animals do not die, animal health and productivity can still be negatively impacted. This can lead to a significant loss of animal products such as meat, milk, and eggs, which can be more than 70%. Human health and nutrition are also affected due to the reduced supply of high-protein food of animal origin such as milk, meat, and eggs [208]. Zoonotic diseases, such as brucellosis, toxoplasmosis, can lead to infertility, abortion, and weak offspring. This can cause great economic losses to farmers and to the whole country.
Zoonotic diseases such as BSE, avian influenza, and anthrax can hamper the international trade of animals and animal products (meat, milk, and eggs) and byproducts across the globe. The economy is also tremendously affected due to measures required for zoonoses control and eradication such as zoonoses surveillance, diagnosis, isolation and quarantine, restriction on animal transportation, treatment and vaccination programs, inspection of meat and milk, and biosecurity. From 1995 to 2008, the global economic impact of zoonotic outbreaks has exceeded 120 billion USD [209]. In the UK, the economic losses due to zoonotic diseases were significant [210]. In 2007, the UK faced drastic food-borne pathogen problem by Campylobacter spp., Salmonella (non-typhoidal), E. coli VTEC O157, Listeria monocytogenes, and norovirus, which caused serious economic losses [211]. In addition, other countries also faced drastic economic losses due to outbreaks of zoonotic food-borne pathogens. For example, Ireland has also suffered a severe economic loss due to Salmonella contamination in its pork products [211]. According to the World Bank [212], Australia has lost 16% of the value of its livestock sector due to outbreaks that impacted beef and sheep. [213]. 2ff7e9595c
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