FOOD BORNE ZOONOSES -CONTROL STRATEGIES
by-DR. RAJESH KUMAR SINGH, (LIVESTOCK & POULTRY CONSULTANT), JAMSHEDPUR, JHARKHAND,INDIA 9431309542, rajeshsinghvet@gmail.com
Any infectious disease which animals can transmit to human beings is called a “zoonosis”
Research indicates that between one third and one half of all human infectious diseases have a zoonotic origin, that is, are transmitted from animals. About 75% of the new diseases that have affected humans over the past 10 years (such as the West Nile Virus) have originated from animals or products of animal origin. Food-borne zoonoses are a significant and widespread public health threat.
Food-borne zoonotic diseases are caused by consuming food or drinking water contaminated by pathogenic (disease-causing) micro-organisms such as bacteria and their toxins, viruses and parasites.
Estimates suggest that almost half of the population of the world is affected by water-
borne and food-borne infections. Food-borne zoonoses are defined as ‘those diseases
contracted from eating foods of animal origin’ such as milk, meat and eggs. This is a broad definition and covers a wide spectrum of pathogens such as bacteria, viruses, and parasites, although the most important on a day-to-day basis are mainly bacteria. Food-borne zoonoses are an important food safety issue worldwide and have also become an important cause of decreased economic productivity in both developed as well as developing countries. Rapid industrialization, change in food preferences and food habits, mass food processing and lack of effective food quality control system has led to the emergence of many food-borne pathogens. More than 250 known diseases are transmitted to humans through food.
Food producing animals (cattle, sheep, goats, pigs, chickens and turkeys) and their products are the major sources for many of zoonotic organisms, which include Salmonella spp., Campylobacter spp., Listeria monocytogenes, Escherichia coli, Yersinia enterocolitica, Clostridium spp., Brucella spp., Staphylococcus aureus, Vibrio spp., Aeromonas spp., etc. as well as food-borne viruses namely Norwalk and rotaviruses along with some food-borne
parasites such as Toxoplasma, Sarcocystis, Cryptosporidium, Trichinella, Taenia, Diphylobothrium etc. These organisms can contaminate animal/poultry carcasses at slaughter or cross-contaminate other food items, leading to human illness and cause huge economic losses.
Typical transmission pathway
An animal suffering from a disease, which may not be apparent, creates a product of
either milk or body tissue in which the causative organism is present. This product is either further processed or directly passed to a final consumer who then either with or without cooking eats the contaminated item, and in susceptible cases develops the disease after a variable
incubation period.
Some of the important food-borne bacterial zoonoses
In many countries of the world, bacterial food-borne zoonotic infections are the most common cause of human intestinal disease. Salmonella and Campylobacter account for over 90 % of all reported cases of bacteria-related food poisoning world-wide. Poultry and poultry products have been incriminated in the majority of traceable food-borne illnesses caused by these bacteria, although all domestic livestock are reservoirs of infection. Other important bacterial zoonoses are cause by Listeria monocytogenes, Escherichia coli, Yersinia enterocolitica, Clostridium spp., Brucella spp., Myocobactreium spp., etc. Some of these important food-borne bacterial zoonoses are described as follows:
Salmonella
Salmonella infections are prevalent all over the world among various species of domestic
as well as wild animals besides poultry, ducks, birds, amphibians, reptiles and rodents. More than 2541 serovars of Salmonella are identified so far. Salmonellosis caused by non-typhoidal species is not only more prevalent but has also shown an increasing trend world over with majority of cases being caused by S. Enteritidis and S. Typhimurium. In India, human
salmonellosis is endemic and one of the most widespread zoonosis. Salmonella organism has been isolated from a variety of foods including pork and pork products, beef, chevon, mutton, fish, milk and its products, fruit juice, fruits and vegetables and egg shells. Animals may be asymptomatic carriers of Salmonella. They may also suffer clinical disease with intestinal
disturbance, septicaemia and death. Transmission usually follows ingestion of infected food, or direct or indirect contact with animal faecal material. In humans symptoms include sickness, diarrhoea, abdominal pain and fever. The most significant serotype in terms of mortality is S.
typhimurium DT104, which shows a 3% mortality rate, being multi-drug resistant to many of the antibiotics.
Campylobacter
Campylobacter are a major cause of gastroenteritis throughout the world. This particular
pathogen is widespread and present in many farm animals. In particular, poultry are very susceptible to heavy bacterial loading. Under normal circumstances, the animals show no sign of
disease, although there have been cases of abortion in sheep being linked to C. jejuni. The bacterium has been isolated from pigs, birds, cattle, dogs, cats, unpasteurized milk and water
supplies. Infection occurs mainly following consumption of faecal contaminated undercooked carcasses especially poultry, or of milk. The organism is capable of surviving freezing and has
been shown to survive for several months in frozen poultry, minced meat and certain chilled foods. The most common symptoms of Campylobacter infection include diarrhoea, abdominal pain, fever, headache, nausea and vomiting. Symptoms usually start 2-5 days after infection, and
last for 3-6 days. Severe complications, such as Guillain-Barre syndrome, may follow Campylobacter infection.
Listeria
- monocytogenes is considered emerging because the role of food in its transmission has
only recently been recognized. The disease is most often associated with consumption of foods such as soft cheese and processed meat products that are kept refrigerated for a long time because Listeria can grow at low temperatures. Outbreaks of listeriosis have been reported from many countries. Several outbreaks of listeriosis associated with consumption of milk and dairy
products have occurred in India. It has been isolated from the milk of cow, buffalo and goat in India. It has also been reported from Seafood, beef, raw milk, vegetables and fresh raw fish. Animals can carry the bacterium without appearing ill and can contaminate foods of animal
origin, such as meats and dairy products. Unpasteurised (raw) milk or milk products made from unpasteurized milk may contain the bacterium. In most cases, infection occurs following ingestion of contaminated foodstuffs. Clinical onset usually follows fever, headache, nausea and
vomiting, and symptoms similar to a severe chill. Abdominal cramps, stiffness of the neck and photophobia may also be present. The condition may progress with organ involvement, including endocarditis, internal lesions, metritis, septicaemia and meningitis. Focal necrosis in the placenta
may occur with spontaneous abortion, premature birth or infective transfer to the baby at birth. A
fatality rate of higher than 20% of clinical cases has been seen when treatment is not made, or is not started quickly.
Escherichia coli
- coli forms a part of most mammalian bacterial gut flora. It has a vast array of
serotypes: some are benign, whereas others are dramatically pathogenic. This can vary from
species to species; a benign form in one animal may be a deadly organism in another. The
particular serotype of major concern is O157:H7, which was first identified as a major cause of serious outbreaks of food poisoning. This serotype is variously known as entero-haemorrhagic E. coli (EHEC), shiga toxin-producing E. coli (STEC) or verocytotoxin-producing E. coli (VTEC) O157. Many outbreaks and sporadic cases have been reported due to STEC in developed as well
as developing countries. It is transmitted to humans primarily through consumption of
contaminated foods, such as raw or undercooked ground meat products and raw milk.
Symptoms of the diseases caused by EHEC include abdominal cramps, haemorrhagic colitis, haemolytic uraemic syndrome etc. The National Salmonella and Escherichia Centre, Kasauli conducted an epidemiological survey of E. coli O157 in different regions of India during the 10-year period (Seghal et al., 2008), in which a significantly high percentage of E. coli O157 was isolated from meat, milk and milk products, seafood and water.
Yersinia enterocolitica
Of the same bacterial genus as plague, it is transmitted to humans by ingestion of foods as diverse as meat (pork, beef and lamb), oysters, fish and raw milk. It causes acute-onset of gastroenteritis with diarrhoea and vomiting, marked fever and abdominal pain. The pain can be
so severe that it mimics appendicitis and has also led to misdiagnosis of Crohn’s disease. It is capable of producing clinical complications which include septic arthritis, colonisation of
existing wounds, bacteraemia and urinary tract infections. Luckily it is rarely fatal.
Clostridium spp.
Clostridium perfringens, the causative anaerobic bacterium of many cases of gas gangrene, may also cause a food-borne disease. Widespread in the environment, and an inhabitant of the gastrointestinal tracts of humans and animals, it is often found in foodstuffs as a
result of faecal contamination. As with other forms of clostridial diseases, it is the production of
exotoxins by the pathogen that causes the main damage, especially where the ingested food carries a large inoculum, or heavy toxin load. The usual pattern of disease is linked to the
ingestion of a number of viable C. perfringens organisms that may produce clinical symptoms of
abdominal cramps, diarrhoea and fever.
Botulism as a complex of disease state arises from contact with C. botulinum or its associated neurotoxin. There are seven types of botulism toxin associated with the bacteria, designated by the letters A-G. Only the A, B, E and F toxins are known to cause illness in humans. Often associated with ducks, geese and some other types of poultry, it can also be found in cattle and horses, which can act as hosts and amplifiers for some strains. The disease usually begins 18-36 hours after the ingestion of the toxin. Early signs include gait difficulties, dysphagia and impaired vision. Respiratory distress, muscle weakness, and abdominal distension and constipation may appear progressively.
Brucella
Brucellosis is a widely prevalent and economically very important bacterial disease caused by Brucella species, of which B. abortus and B. melitensis are the main causes of occupational zoonosis in farmers, veterinarians and workers in meat industry. It is common in
organized herds and in areas with high rainfall and humidity. Source of infection in human is through the drinking of infected raw milk or unpasteurized milk, handling of aborted foetus, fluids and foetal membranes, slaughter house workers and butchers contract infection while handling foetuses, after births or by contact with vaginal secretions, veterinarian gets infection
during rectal examination without wearing gloves and while conducting post mortem examination, through skin abrasions and conjunctiva. There are losses due to abortion in the
affected animal population, loss of progeny and reduced milk production. In humans disease is clinically characterized by chills, profuse sweating, weakness and fatigue, insomnia, sexual impotence, headache, arthralgia and generalized malaise, which last for weeks and months;
commonly shows remissions (hence also known as undulant fever).
Mycobacterium
Tuberculosis caused by Mycobacterium bovis needs no introduction. Human-to-human spread of resistant serotypes of M. tuberculosisis now more significant than the bovine form
acquired from dairy products. Ingestion and inhalation are the most common mode of transmission. Consumption of infected milk and milk products is the mode by which food borne zoonoses occur. It is a chronic disease of man and animals causing development of tubercle in vital organs. The pulmonary tuberculosis is the most common form, characterized by cough, fever, fatigue, weight loss, chest pain and night sweat in human beings.
Some of the important food-borne viral zoonoses
Numerous viruses can be found in the nature, but only a few are commonly recognised as important food borne pathogens. These can be classified into three main groups, according to the type of illness they produce:
Viruses that cause gastroenteritis such as Norovirus, Enteric adenovirus (types 40/41),
Rotavirus (group A – C), Sapovirus, Astrovirus, Coronavirus.
Enterically transmitted hepatitis viruses (Hepatitis A and E); and
A third group of viruses that replicate in the human intestine but cause illness after they migrate to other organs, such as the central nervous system or the liver such as Enteroviruses.
Food borne illness has been documented for most of these viruses, but recent studies show that the Noroviruses (NoV) and hepatitis A virus (HAV) are by far the most common cause of illness
by this mode of transmission. Some large food borne outbreaks have occurred with group B and C, rotaviruses, and waterborne outbreaks have occurred with hepatitis E virus. These viruses are
spread by the faecal-oral route, cross-contamination and infected food handlers. Rotaviruses, classified in the reoviridae family, are ubiquitous and have been isolated from a variety of
mammalian species. Rotavirus has been recognized as one of the most common cause of severe gastroenteritis in a wide variety of animal species including children, calves and piglets
worldwide.
Outbreaks of rotaviral gastroenteritis are frequently observed in institutional settings such as hospitals, nursing homes, day-care centers, and schools. The incidence is higher during winter season in temperate climate whereas, no seasonal variations for tropical countries. However, certain studies reported higher incidence during rainy season. In developing countries, Norwalk
viruses are so common that a very high percentage of children develop immunity at an early age. Generally the illness that results from Norwalk viruses is mild and brief. Foods are contaminated with Norwalk viruses via the faecal-oral route and contaminated water. Salads, insufficiently
cooked clams and oysters, ice and water are the most commonly implicated foods. Common symptoms in viral food borne zoonoses include nausea, vomiting, diarrhea, abdominal cramps,
headache, fever/chills, muscle aches. Symptoms usually last 1 or 2 days. However, during that brief period, people can feel very ill and vomit, often violently and without warning, many times
a day.
Some of the important food-borne parasitic zoonoses
Food-borne parasitic zoonoses cause death and serious diseases in humans and animals worldwide, and are of both public health significance and socioeconomic importance. Food
borne parasitic infections have been recently identified as an important public health problem having considerable economic impact in terms of morbidity, loss of productivity and health care
costs. Poor sanitation and traditional methods of food preparation accelerated the spread of food borne parasitic infections. Some of the important food-borne parasitic zoonoses are described as
follows:
Toxoplasmosis
Toxoplasma gondii is possibly the most wide spread and prevalent protozoan parasite on
earth, infecting approximately half a billion people. Toxoplasma gondii is a parasite of domestic and wild cats that potentially is capable of infecting all vertebrates. Toxoplasmosis can be
transmitted to humans via several routes. Although a major source of infection is thought to result from contamination of the environment with oocysts shed in cat faeces. Transmission of
T.gondii by ingestion of tissue cysts in raw or under cooked meat from a variety of livestock and game animals has been documented as another major source of human infection. It is characterized by retinochoroiditis and encephalitis, and abortion in pregnant women (especially at first trimester). In animals, it causes abortion especially in sheep.
Sarcocystosis
Sarcocystis spp., like T .gondii, is coccidian protozoan which have a global distribution. Humans acquire S. hominis by consumption of uncooked beef containing zoitocysts. Sarcocystis
hominis is only mildly pathogenic in humans, causing stomach pains, nausea and diarrhoea; Sporocysts begin to be passed in the faeces after 14 to 18 days (11 to 13 days after infection with S. suihominis). Sarcocystis suihominis is acquired by eating zoitocysts in under cooked pork. Sarcocystis suihominis is more pathogenic than S. hominis, causing stomach pains, nausea, diarrhoea and dyspnoea within 24 hours of infection.
Cryptosporidiosis
Cryptosporidium spp. are spore-forming parasitic protozoans found widely in the
environment in an extensive variety of foodstuffs, including salad and vegetables, raw meat and
meat products, offal and milk, usually associated with contamination arising from animal faecal matter. Cryptosporidium parvum is considered to be a particularly significant pathogen. Calves, lambs and deer have been identified as asymptomatic animal reservoirs, capable of shedding viable organisms in their faeces. Human infection follows either direct contact with animal faeces or consumption of inadequately cleaned or cooked products. Following a pre-patent period of between 2 and 14 days and in individuals with no underlying risk factors, there is profuse self-limiting watery diarrhoea, with abdominal pain and cramps, and a low fever that may last up to 7 days.
Taeniosis or Cysticercosis
Taenia solium (tapeworm of pigs) and T. Saginata (tapeworm of cattle) have cosmopolitan distributions with the former being more widespread in the rural areas of Latin America, Africa
and Asia. Cysticercisis is caused by the intermediate stages of the tape worms Taenia solium and Taenia saginata. It is clinically characterized by abdominal pain, anorexia, nausea,
diarrhoea and constipation, loss of body weight and debility. Nervousness and insomnia may also occur. Human beings are universally susceptible to taeniosis. Infection is more common in
low socio-economic group of the people. Larvae (Cysticercus cellulosae – measly pork) and (Cysticercus bovis – measly beef) fully develop in the different predilection sites, such as heart,
diaphragm, internal masseter, tongue, neck, intercostals and abdominal muscles, less commonly brain, liver, lung, kidney and eye after reaching to the blood by penetrating the intestinal wall
when infected eggs are consumed. This is the infective stage for human beings. Man gets infection by ingesting measly beef or pork undercooked. Cysticercosis is more serious than
taeniosis in humans. It recognized as:
Myocysticercosis: Muscular cramps, pain and muscle fatigue.
Ocular cysticercosis: Presence of cysticerci in vitreous humor and anterior chamber of eyes leads to uveitis, iritis, retinitis and palbebral conjunctivitis.
Neurocysticercosis: Signs depend on the location of the cyst found on the brain. Usually it found in the meninges, cerebral cortex and ventricles. So, symptoms of meningitis, epileptic encephalitis, headache, ataxia, nausea, vomiting and visual disturbances may be observed.
Trichinellosis
It is a type of food-borne helminthosis, caused by Trichinella spiralis. Trichinellosis can occur where humans eat raw or improperly cooked meat or meat products from infected pigs,
wild boars, horses, walruses, dogs and many other domestic or wild mammals. Number of larvae ingested by humans determines the clinical disease. Usually 10 to 100 parasites per gram of muscle cause clinical signs. It is clinically characterized muscle soreness and pain due to irritation, enteritis, edema of upper eyelids, thirst, profuse sweating, chills and eosinophilia, and eventually, death due to myocardial and respiratory failure may occur.
Control strategies
Control of food borne disease is a multifaceted process, as there are no vaccines available
for most food borne pathogens. The prevention of infection requires control measures at all
stages of the food chain, from agricultural production on the farm to processing, manufacturing and preparation of foods in both commercial establishments and the domestic environment. The general strategy of control is to understand the mechanisms by which contamination and disease transmission can occur well enough to interrupt them. Increasing liberalization of trade, and increasing competition in the international market place, have meant that live animals, animal feed, food ingredients and products are now sourced on a global stage, affording the opportunity for zoonotic pathogens to be disseminated widely. The public health veterinarian needs to be proficient in setting up surveillance systems to monitor trends, establish priorities, inform policy-makers and control interventions. Understanding the likely routes of infection and the life cycle of the pathogen allows selective measures to be applied in a focused way, breaking the transmission route at its weakest point. Different basic steps to prevent the occurrence of these
food borne infections are discussed below.
Step 1: Control the disease in the animals
The effective control in the food chain requires the incidence of infection in animals to be
reduced. The health of consumers is inextricably linked to the health of food producing animals and the importance of herd and flock health cannot be underestimated. The incidence of zoonotic
disease in animals may be reduced by the use of vaccination, clean foodstuffs and water, and good housing and husbandry practices. Overcrowded or unsanitary conditions can often lead to
overt disease or unthrifty animals, requiring more therapeutic support for them to maintain sufficient health to attain slaughter weight or to continue to be productive. A reduction in
infection rates has a dramatic effect on the incidence of infection further down the food or product chain. The associated lower levels of contamination produce a lower likelihood of illness.
Step 2: Reduce contamination at harvesting
When eggs are picked out, or cows milked, the application of sensible hygiene precautions is essential. Eggs should be free of droppings and cleaned and date marked. In
dairies, the udder of the cow and the milking machinery should be as clean and hygienic as possible, with subsequent disinfection after each milking. Pipe work and items such as clusters should be maintained and replaced as necessary to maintain adequate operating parameters. Milk
should pass to a bulk tank and be subsequently chilled rapidly for later transport and pasteurization. At abattoirs, tight veterinary inspection both pre- and post-slaughter must be
practiced. Animals that display heavy faecal contamination should be cleaned or rejected.
Slaughterhouse controls should prevent or reduce onward transmission into the food chain, with rejection of suspect carcasses. Prompt refrigeration of meat and careful cleaning of the carcass
can reduce bacterial contamination drastically.
Step 3: Retailing controls
Disinfection of working tools and areas, along with personal and premises hygiene
procedures protect consumers and workers from zoonotic infection. Sourcing products from
assured suppliers, temperature and environmental monitoring, and the separation of cooked and raw products reduce the possibility of amplification and transmission of infection. The tight control of ‘use-by’ and ‘sell-by’ dates is mandatory, as is periodic inspection by public health officials, and the implementation of monitoring of refrigeration and freezer plants.
Step 4: Domestic precautions
In the home, consumers should use common-sense measures, including disinfection of surfaces and equipment, personal hygiene procedures and thorough appropriate cooking techniques. Using a refrigerator correctly and observing sell-by dates would prevent many cases
of food poisoning.
There are several factors that continually contribute to the occurrence of outbreaks of food-borne disease and often several of these occur simultaneously, thus amplifying outbreaks. These factors
include: contaminated raw ingredients (including water), inadequate refrigeration or storage, insufficient cooking, cross-contamination between raw and cooked food, poor personal hygiene
of staff, poor general hygiene on premises, and untrained staff. Robust food safety management systems with adequate process controls are essential with good manufacturing practice and
hazard analysis and critical control points (HACCP). Prior to establishing HACCP, good food hygiene standards must already be in place, particularly in the following areas:
Infrastructural and equipment requirements.
Food safety specifications for raw materials.
The safe handling of food (including packaging and transport).
Sanitation (cleaning and disinfection).
Water quality.
Maintenance of the cold chain.
The health of staff.
Personal hygiene.
Training.
Food waste handling.
Pest control.
These standards are designed to control hazards in a general way and they are clearly prescribed in the Codex Alimentarius.
Conclusions
Food-borne zoonotic diseases are caused by consuming food or drinking water contaminated by pathogenic (disease-causing) micro-organisms such as bacteria and their toxins,
viruses and parasites. They enter the body through the gastrointestinal tract where the first symptoms often occur. The risks of contamination are present from farm to fork and require prevention and control throughout the food chain. To protect consumers from these food-borne zoonoses, an integrated approach to food safety from the farm to the fork is needed to be
adopted.
