Live and Wet Markets (LWMs) : A continuing Source of Emerging Infectious Diseases

Live and Wet Markets (LWMs) : A continuing Source of Emerging Infectious Diseases

 

Wet markets in Southeast Asia have recently gained widespread attention because origins of the COVID-19 pandemic have been linked to a wet market in Wuhan, China as with the 2003 SARS pandemic.

Zoonotic diseases have potential to cause global pandemics; large-scale outbreaks of zoonoses, resulting in huge numbers of deaths, have caused significant disruption to economies, political order, and societies throughout history .These diseases can spread from animals to humans where there is an interface allowing pathogens to jump species, such as in a farm or a market.Live and wet markets (LWMs), markets selling live animals, and animal products (sometimes called traditional, as opposed to modern markets), are widespread in the growing cities in low- and middle-income countries (LMICs), including those in Asia and Africa. Many people depend on these markets for their livelihoods and food supply. The interaction of humans, both retailers and customers; live animals for sale; food products, including ready-to-eat food, as well as wild and peri-domestic animals, pose important risk factors for emerging infectious diseases. But LWMs also bring many benefits, for example, their cultural significance has brought numerous international tourists to visit local LWMs .The markets are accessible to local consumers; they often sell traditional and well-liked foods, and they foster personal relations between buyers and sellers. Yet, these markets, while providing customers with animals to consume, or animal-sourced foods, undoubtedly act as an interface for virus exchange with a high risk of cross-species transmission to humans . The recent history of outbreaks of coronaviruses (CoVs) and avian influenza viruses (AIVs) has well illustrated that these emerging zoonotic diseases, originating from animals in LWMs, can present threats to human health .The impact on health and economy in LMICs by zoonotic infections spread in LWMs is likely largely underestimated, but perhaps also the importance of these markets on livelihoods, nutrition and psychosocial wellbeing is also underestimated.

Figure 1Potential for Viral Emergence in Live and Wet Markets.

 

By categorizing known pathogens, one study found that over 60% of human emerging infectious diseases are zoonotic, and the majority of these (72%) originate in wildlife , while another estimate was that 75% of emerging pathogens were zoonotic . While estimates vary, there is overall consensus that most emerging viruses originate from animals. Many emerging epizootic and zoonotic virus infections involve single-stranded RNA viruses, such as coronaviruses, capable of causing infections that can be most severe in both animals and humans. Recently 1445 novel RNA viruses were discovered in invertebrates and more than 200 previously unknown viruses were found in vertebrates . The true extent of the ‘virosphere’, however, remains largely unknown and still needs to be explored in depth. Most RNA virus populations exist as complex mixtures of genetic and phenotypic variants, as a result of the high RNA polymerase error rate . However, these errors may also be lethal for the virus, which coronaviruses seem to avoid by having an increased proofreading capacity. The high rate of mutation creates diverse viral populations, which increases the likelihood that some variants can adapt to a new environment or a new host, and thus facilitate new emerging virus variants. Moreover, changes in natural conditions often drive genetic evolution, such as genetic reassortment and recombination, possibly resulting in the transition of microbes from nonpathogenic to pathogenic, from low virulence to high virulence, thus causing emergence of zoonotic diseases . Cross-species transmission and the ability to sustain many cycles in the new host, which is needed for human-to-human transmission, require that the virus has the ability to interact with receptors in the new host . It has been hypothesized that viral evolution in the new host depends on the trade-off between virulence and transmission . This is exemplified by the different human CoV epidemics, in which Middle East respiratory syndrome (MERS) CoV has a high case fatality, but transmits less frequently than severe acute respiratory syndrome (SARS)-CoV-2, which has lower case fatality .Factors that connect naïve hosts with pathogens, including crowding, urbanization, increasing human populations with immunosuppression and comorbidities, deforestation, fragmentation of natural habitats, agricultural intensification, and globalization, could be drivers for viral shifting . These factors are prominent in many LMICs today. The growing population has growing needs for food, particularly in large cities with substantial middle-income classes, with the demand for animal-source food increasing, driven by increasing population, urbanization, and wealth . Meeting this demand for perishable products is not without its challenges. In countries lacking infrastructure, it can be impossible to transport animal-source foods over long distances, especially in tropical temperatures. Lacking a cold chain, people prefer purchasing live animals or fresh meat, and often animals are trekked or transported across considerable distances from rural to urban areas or from urban and peri-urban farms. However, despite the increasing availability of affordable refrigeration, the demand for live animals or fresh meat in wet markets persists, as people believe that fresh meat is safer, tastier, and more natural . Moreover, even in urban areas, household cold storage may be lacking, and electricity ‘outages’ or failures are common. Also, in many cultures, households prefer to buy fresh food every day rather than buying in bulk and often value the social interactions experienced in LWMs.

One organism has baffled the entire world and every segment of life has undergone turmoil in terms of health, education and economy. Several families ruined and faced the heat of Covid 19 infection. People thought of only survivability rather than their achievements. It is due to a “zoonotic disease” that originated from animals and spread to humans. This is all due to the human errors creating wet markets.

Most people had not heard the term “wet market” before the COVID-19 pandemic. The term gained almost universal acknowledgement once it came to light that the source of the outbreak of the coronavirus was the Huanan Seafood Wholesale Market, a wet market in Wuhan city, China.

In these we markets close interactions with wild animals have caused numerous disease outbreaks in humans, even before the occurrence of coronavirus. Similar conditions, including Middle East respiratory syndrome (MERS) and Severe Acute Respiratory Syndrome (SARS), have been caused by virus strains with zoonotic origins, meaning that they originated in an animal host before spilling over to human populations.  Some of the viruses such as  HIV, Ebola, Nipah virus, Avian Influenza (bird flu) and H1N1 (swine flu) also have zoonotic origin .

Live and wet markets have been linked to the emergence of different epidemic/pandemic diseases, including coronavirus disease 2019 (COVID-19) and different subtypes of influenza ‘A’ viruses, and they are also an important source of foodborne pathogens.

A report on Zoonotic Diseases states that 75%of emerging diseases are of zoonotic origin. Centers for Disease Control and Prevention reported that every 3 out of 4 new emerging infectious diseases in people are traced back to animals.

What is a wet market?

Wet markets sell products that are perishable, such as animal products, fruits, and vegetables, as opposed to dry markets that sell non-perishable items including electronics and clothing. Some wet markets sell living animals who are slaughtered upon arrival or upon purchase from customers at the market. Though less uncommon, some wet markets sell wildlife and are connected to the wildlife trade, which is illegal in many countries and for certain endangered species.

These markets are called wet due to the state of the floors. They are generally located in the open air or in large vaulted buildings. Because of a lack of air conditioning, water is constantly sprayed over the produce to keep it cool and fresh. Meat, butcher blocks, and vendor stalls are also sprayed continually to keep areas as clean as possible and to wash away the blood from slaughtered animals.

Wet markets also use a lot of ice. The bodies of recently slaughtered animals must be kept cool to stave off bacterial or pathogenic growth. If a customer only wants a certain portion of the animal, the vendor will likely continue to process the body and keep it on ice until the next customer comes. This melting ice, along with spillage from seafood tanks, and the blood and entrails spilled during the slaughter process contribute to the soaked floors of these markets. Pieces of bodies that aren’t purchased pile up, attracting insects and bacteria. This combination of melting ice, blood, and body parts creates the wet floors these markets are known for.

A wet market typically has multiple open-air stalls, spread over a large area, where vegetables, fruits, meat and fresh seafood are sold. Some of these sell and slaughter live animals, including poultry and fish, on-site, while some even engage in illegal dealings of wild animals. A wet market is dubbed so because, in such a market, water and ice are used to keep the food and meat fresh.  On the contrary the dry market is a market selling clothing, electronics, etc. rather than fresh meat and other dry produce.

The wet markets are supplying meat from several animal species including wild animals and sea food to millions of people in the world, precisely the countries like China, Taiwan, Indonesia, Singapore is having live and wet markets (fig.,2,3,4&5). In these markets selling of variety of animals including, wild life such as wild ducks, peacocks, monkeys, pangolins, bats, foxes, rodents snakes and other reptiles etc.

The human greed has created the areas with thickly populated, less ventilation and contamination with substandard hygiene and sanitation has all created an unhygienic environment conducive for emergence of newer infections in such market areas.

 Indian meat market.

The Indian meat, poultry, and seafood are largely dependent on wet markets^[. According to Food & Beverage News, domestic consumers prefer freshly cut meat from wet markets over processed and frozen meats despite use of outdated and unhygienic facilities by the majority of Indian wet market abattoirs.

Indian wet markets as seen in  at Ghazipur Murga Mandi in Delhi slitting live chickens’ throats, skinning the birds, and sorting through their flesh, which was soaked in blood and guts, with their bare hands. There were bags of live, struggling crabs and eels at a fish market in Malancha, West Bengal. Captured dogs were killed and sold for meat at the Keera Bazaar in Dimapur, Nagaland, and near Mao Market in Kohima, Nagaland. (Nagaland has just decided to stop dog-meat sales, but the illegal trade continues in other states.) In Manipur, sellers at the Nute Bazaar handled the charred remains of wild animals – including monkeys, wild boars, porcupines, and deer – and at the Churachandpur market, meat from various wild animals was sold.

 

Wet Markets Around the World

Wet markets are common all over the world. Much like farmer’s markets, each wet market differs widely in terms of offerings, based on product availability, geographic location, and other factors like cultural and religious cuisines. Wet markets don’t exclusively sell animals and many only sell live animals such as fish. Some wet markets, including the Huanan Seafood Wholesale Market thought to be the site of the original transmission of the novel coronavirus, sell “exotic” or wild-caught animals. It is these so-called wildlife markets that pose the greatest risk of zoonotic transmission.

Wet markets can be the main source of both food and income for countless people all over the world, and they serve as places of community where customers and vendors develop relationships that last years. If wet markets were shut down today, it would have a catastrophic impact not just on the vendors who would lose needed revenue streams, but on all of the people that rely on the markets to buy the food meant to sustain their families. Not only this, but such a broad-strokes approach may be ineffective against zoonotic disease spread since this threat is most significant at markets that sell wild or exotic animals.

People everywhere deserve to have access to healthy, safe food. Yet in some ways, food systems fail everyone – humans, animals, and the environment. Industrial agriculture, which supplies countries including the United States, is rife with such failings at nearly every level. Wet markets too present difficult questions that need addressing. Beyond the glaring welfare issues regarding animals forced to live in squalor and fear leading up to their imminent slaughter, the lack of sanitary enforcement and extremely messy (for lack of a better word) conditions make the possibility of future zoonotic diseases and global pandemics a very real threat.

 

Advantages of wet market

• The growing trend of protein intake among health-conscious consumers has also amplified the consumption of meat products and is expected to drive the market revenue over the coming years.
• It Creates ample employment-and place to set small-scale meat and agro-industry.
• Ease of Access to Consumers- to buy vegetables from one stall and get meat from the one next to it.
• Where wet markets are beneficial for farmers to meet costumers easily, consumers also get the advantages of wet market by finding every needed item in one place.

Disadvantages of wet market

• Wet markets have all sorts of unhygienic practices unsanitary enclosures are a friendly source for Zoonotic diseases to mutate and evolve as a vending stall.
• Butchering endangered species of animals in return for substantial monetary benefits. Killing these animals for money or just for the sake of good taste doesn’t seem acceptable to animal lovers.
• Meat markets, Illegal Selling, of -Peacocks, lizards, wild bats, Pangolins, monkeys, and other trafficked species are potential source viruses and microorganisms responsible for the widespread of a pandemic and health concern.

Care of meat and stored meat: Safety is important when you are buying meat.

• Ground meat and offal like liver and kidneys should only be kept in the fridge for one to two days.
• Leftovers containing cooked meat should be kept for no longer than three to four days before tossing.
• When you buy packed and stored meat examine the expiry date
• Care need to be exercised to see any tampered packing or contaminated with other meat or food items in the deep freeze.
• Store the meat items in deep freeze or in its designated area in freeze.
• Use stored meat within 3- 5 days.
• Wash your hands before and after handling of meat.
• Cook the meat at 145 to 160o F.
• Put meat, poultry, and fish in separate plastic bags so that their juices don’t get on your other foods.
• Freeze raw meat, poultry, or fish if you won’t be eating for several days. Keep unopened packages of hot dogs and deli meats in the refrigerator for up to 2 weeks.

Food Safety and Standards (Food Products Standards and Food Additives) Regulations, 2011 also warrant that every product being sold in the Indian mark.et must meet/conform to legal standards of quality.

There are three principles of meat hygiene, which are crucial for meat processing operations.

• Prevention of microbial contamination during meat product manufacture by adopting proper cleaning and sanitation practices.
• Minimization of microbial growth in meat products by storing them at a low temperature
• Reduction or elimination of the risk of microbial contamination by applying suitable heat treatment and packaging systems at the final processing stage.

Pathogens

Poultry and poultry meat are often found contaminated with potentially pathogenic microorganisms such as Salmonella, Campylobacter, S. aureus, E. coli and Listeria. In some occasions also Yersinia enterocolitica, Aeromonas and Cl. perfringens have the potential to be important pathogens in poultry products. However, Salmonella, Campylobacter and to a lesser extent Listeria, are considered to be the major food-borne pathogens in the poultry industry. Besides these the emergence of Aeromonas from poultry meat products as a vector of human infection has also been reported. Among Aeromonas spp. detected on poultry carcasses, Aeromonas caviae, A. hydrophila, Aeromonas salmonicida-masoucida, and Aeromonas schuberti have been reported to survive after 14 days of product storage.

Regulations and Legislation in India

In India, only goat, sheep, pigs, bovine or cattle, poultry, and fish are allowed to be slaughtered. Animals such as sea turtle, porcupines, lizards, etc. are species that are protected by law, and slaughtering of these animals is illegal.

Food Safety and Standards Authority of India (FSSAI) was set up to provide the licenses and see that the guidelines and measures are met. The most important legislation is the Food Safety and Standards Act, 2006 (FSSA), that overrides all other food-related laws in operation prior to it. FSSA initiates harmonisation of India’s food regulations according to international standards.

The Food Safety and Standards (Licensing and Registration of Food Business) Regulations, 2011 govern the aspect of license and registration of food businesses, including meat and meat-based products. Under Regulation 2.1, all food business operators in the country are required to be registered. A valid license is needed for any food-related operation and to ensure safety, sanitary and hygienic conditions.

But according to a Down–To-Earth report, the organization is ill-equipped and underfunded to properly carry out the work

An Overview of Zoonotic Pathogens with High Potential for Spread through Live Animal and Wet Markets

Pathogens	Original animal/natural host	Potential for spread in markets	High-risk area
Crimean–Congo hemorrhagic fever virus	Ticks, ruminants	Live ruminants brought to markets could spread virus through body fluids, or through vectors	Africa, the Balkans, the Middle East and Asia
Ebola viruses	Bats and/or primates	Sale of live exotic animals or bush meat brings the pathogen close to humans	West and Central Africa
Hantaviruses	Rodents, shrews, moles, bats	Reservoir animals may be sold at markets, but scavenging rodents may also bring the pathogens close to the markets and contaminate products	Worldwide
Hepatitis E virus	Domestic pigs, wild boars and maybe other animal species	Spread through food products or contacts with live animals at market	Worldwide
Avian influenza virus	Wild birds, poultry	Infected birds can transmit the virus to humans	Worldwide (mainly in Southeast Asia and the Middle East)
Marburg virus	Fruit bats of the Pteropodidae family	Bats sold at markets, or products contaminated by bats	sub-Saharan Africa
Monkeypox virus	Monkey	Through bush meat or live animals sold at markets	West and Central Africa
Nipah virus	Fruit bats, pig	Contaminated food products or live animals sold	South and Southeast Asia
Rabies virus	Carnivores, bats, dogs	Not transmitted by food, but, by bringing carnivores or bats live to markets, there is a risk of bites. Similarly, markets may attract scavenging dogs, increasing risks for bites	Africa and Asia
Coronaviruses	Bats, mammals	Large variety of coronaviruses could be brought by live animals taken to the market; some of these viruses may have zoonotic potential	Worldwide
Vector-borne viral disease	Mosquitoes and ticks	Wet markets could provide breeding grounds for mosquitoes and ticks in urban settings	Worldwide
Leptospira spp.	Livestock, rodents	Could be brought to markets through infected animals for sale, but also risk of scavenging rodents spreading the pathogen in the environment	Worldwide, with a higher incidence in tropical climates

 

 Hygiene Of Wet Markets 

There have long been concerns with hygiene in wet markets. Stressed and frightened animals who may be infected with diseases can urinate, defecate, and excrete other biofluids in essentially the same areas where they are killed and their meat is taken by customers. This is a major factor in disease contamination. Further, fragments of animal bodies, such as gills, fins, and other discarded pieces are sprayed onto floors, which can pile up around the feet of both vendors and customers, providing further opportunities for the transmission of diseases.

The equipment used in wet markets can also be sub-optimal. The chopping blocks used to kill and process animals can be made out of wood. One study investigated wooden cutting boards in wet markets on Hong Kong Island, finding that most surfaces harbored micronisms associated with infections found in hospitals, as well as the presence of antibiotic-resistant genes.

Zoonotic transmission in wet markets can also come from animals considered to be pests that thrive in these environments. One study looked at rat populations in the wet markets of Thailand, finding that rats are a potential reservoir of zoonotic transmission of pathogens including Salmonella since they live within intimate contact of humans and their food.

The Risk of Transmitting Zoonotic Diseases

Wet markets that sell live animals have been linked to the emergence of past pandemics. In Hong Kong, a live poultry market transmitted 18 cases of bird-influenza, killing six people. In 2003, a wet market in Shenzen, China caused a SARS coronavirus outbreak due to selling Himalayan palm civets.

Zoonotic diseases are transmitted due to close contact between animals and human beings. The Center for Disease Control states that over half of all known infectious diseases are zoonotic in origin and that 3 out of every 4 new infectious diseases in people coming from animals. What makes wet markets an ideal breeding ground for zoonotic transmission is the diversity of species that can be brought into close contact with humans, especially wildlife. Under more controlled conditions, such as those on western-style factory farms, animals are fed antibiotics their entire lives, thereby limiting the spread of disease (although antibiotic use in factory farms causes other serious health problems in people, such as antibiotic resistance and diseases arising from environmental pollution).

Another key ingredient to zoonotic transmission is cortisol, which is produced in animals, including humans, who are experiencing fear or anxiety. Unfortunately, wet markets can be extremely stressful environments for animals. After enduring long and often painful journeys to the market, animals can be forced to witness the deaths of their companions. The stress this causes animals is likely quite significant.

Under normal circumstances, when an animal’s immune system is confronted with a pathogen, the body responds by generating inflammation to combat it. However, when cortisol is released into the body, the immune-inflammatory response can be repressed, allowing pathogens to proliferate. Human beings sharing close quarters with diseased animals, or eating their flesh recently after death, can create ideal conditions for zoonotic transmission.

Wet Markets After Coronavirus Outbreak

Wet markets will continue to be widely patronized around the world after the coronavirus pandemic. However, in recent years, trends have been observed that point towards decreasing popularity of these places, in favor of other retailing options such as grocery stores, supermarkets, or online retailers. Younger generations tend to be driving these trends.

Many experts agree that ending the wildlife trade is of paramount importance if future pandemics are to be avoided. The international wildlife trade is a multibillion-dollar industry, with one study estimating nearly 9,000 species will be at risk of extinction due to the international trade in animals for pets, food, and medicines.

In response to COVID-19, Beijing temporarily banned all trade in wild animals for food, and the Chinese government continues to explore laws that may stem the trade. The biggest problem, however, lies in the demand. As long as people continue to consume wild or “exotic” animals for food or medicine, the wildlife trade will continue, with some suggesting it may simply go underground if it is made illegal.

 Conclusion

Wet markets are unsanitary conditions and are ideal for spreading disease, and experts believe that the novel coronavirus – which has already killed over 500,000 people worldwide – first infected humans through wildlife in a wet market in Wuhan, China, although one theory links the disease to factory-farmed pigs. Similar situations may arise from our wet markets also and any food-related operation and to ensure safety, sanitary and hygienic conditions. We should also think to establish good market chain for selling  hygienic processed meat and poultry, without wet market contamination in near future.

Prof. K.Ravi,IVRI

Reference-on request

 (Source: Google Images)