Annex 6
Objective 6: Veterinary and HumanDisease Risks
Contents
1.Hazard Identification & Characterisation
/ 21.1 Livestock Diseases
/ 21.2 Bacteria
/ 21.3 Common Foodborne Bacteria
/ 21.4 Other Bacteria
/ 31.5 Viruses
/ 41.6 Parasites
/ 61.7 Prion Diseases
/ 71.8 Mycotoxins
/ 71.9Heat Treatment
/ 82.Disease Risk Assessment
/ 9References
/ 10Table 1. Potential Food waste-borne Infectious Disease Agents of Ruminants, Pigs and Poultry.
/ 16Table 2. Disease Risks from pathogens of Ruminants, Pigs and Poultry contaminating Food waste. / 22
1.Hazard Identification & Characterisation
Food waste containing meat or meat products can be a potential source of infection from a range of bacteria (including antimicrobial-resistant strains which may also be able to transfer resistance genes to new hosts) viruses, and parasites.Contaminated foods can also lead to exposure to various toxins. Whilst prion diseases would also pose a serious risk from food waste, there is stringent legislation in force requiring the removal and disposal of Specified Risk Material (SRM) at the abattoir prior to entering the food chain. The feeding of food waste to livestock has therefore been implicated as a means of international transmission of major exotic livestock diseases, and of the spread of these diseases within infected countries.
1.1Livestock Diseases
Bacterial, viral and parasitic disease agents of livestock considered in the risk assessment are listed in Table 1. As bacterial identification and classification are constantly changing, the terminology used in this report will follow the classification based on the International Code of Nomenclature of Bacteria system wherever possible. The system of virus classification referred to throughout is that used by the Foodborne Viruses in Europe network (FBVE) joint electronic database to ( (Koopmans et al., 2003). For parasites the system of classification is that used by standard parasitological texts (Taylor Coop and Wall 2007). Many of the listed agents are also zoonotic.
1.2Bacteria
Many bacteria can cause foodborne illness in humans and disease in animals. In the UK, Campylobacter, Salmonella, Escherichia coli and Clostridium are the commonest bacterial causes of foodborne infection in humans. In addition to disease caused by direct bacterial infection, some foodborne illnesses are caused by exotoxins which are excreted as the bacteria grow, and they can cause illness even when the microbes that produced them have been killed.
1.3Common Foodborne Bacteria
Campylobacter jejuni is recognized as one of the main causes of bacterial foodborne disease in humans in many countries, with poultry an important source of infection (Hermans et al 2012). WhileC. jejuni is the commonest species found in poultry it is not considered to be pathogenic in poultry, unless co-infections with other pathogenic organisms are present. C. coli frequently infects pigs (Thakur and Gebreyes, 2005), and can cause foodborne disease in humans (Humphrey et al., 2007). C. fetus is a cause of spontaneous abortions in cattle and sheep, as well as an opportunistic pathogen in humans. The common route of transmission is by the ingestion of contaminated food or water, and the eating of raw meat, particularly poultry in humans. Infection in calves produces diarrhoea, sometimes bloody, mainly in young animals.
Salmonella infections are zoonotic and can be transferred between humans and animals. Current nomenclature suggests that Salmonella consists of two species -S. enterica and S.bongori, with six subspecies; however, traditional nomenclature is still commonly used by specialists in microbiology. Many infections are due to ingestion of contaminated food. Thus food is an important infection route for enteriticSalmonella including those that are resistant to antimicrobials (European Food Safety Authority, 2006). Antimicrobial-resistant Salmonella causing foodborne human disease are well documented. Implicated foods are typically beef, pork, poultry, dairy products, but also eggs and fresh produce.
Virulent strains of Escherichia coli (enteropathogenic [EPEC], enterohaemorrhagic [EHEC] and enterotoxigenic [ETEC] strains) can cause gastroenteritis, urinary tract infections, and neonatal meningitis. Infections with multi-resistant E. coli are an important public health problem. Transmission of pathogenic E. coli often occurs via the faecal-oral route. Common routes of transmission include unhygienic food preparation, and a range of food products have been associated with E. coli outbreaks. Dairy and beef cattle are primary reservoirs of E. coli O157:H7 and can carry it asymptomatically and shed it in their faeces. Enteric colibacillosis is a common disease of young calves and piglets caused by colonisation of the small intestine by enterotoxigenic strains of E.coli.
Clostridia are a group of obligate anaerobic bacteria consisting of around 100 species that include common free-living bacteria as well as important pathogens in animals and humans. Clostridia are motile bacteria that are ubiquitous in nature and are especially prevalent in soil and decomposing plant material. Some species are normal inhabitants of the intestines and, after the death of the animal, rapidly invade the blood and tissues playing a major role in decomposition of the carcass. Pathogenic clostridia affecting cattle and sheep have been divided into three main groups. Neurotrophic clostridia include C. tetani and C. botulinum, which produce powerful neurotoxins giving rise to the diseases tetanus and botulism respectively. Histotoxic clostridia produce exotoxins that cause local tissue necrosis and systemic toxaemia. Examples include C. chauvoei, the major cause of blackleg; C. novyi type B, which causes black disease; C. septicum which causes malignant oedema and braxy; C. haemolyticum (C. novyi type D), which causes bacillary haemaglobinuria; and C.sordelli which causes gas gangrene. Enterotoxic clostridia include C. perfringens type D, which causes pulpy kidney disease; C. perfringens type C, which causes struck; and C.perfringens type B, which causes lamb dysentery.
C. difficile is a commensal bacterium of the human intestine but has become increasingly important as a cause of antibiotic-associated diarrhoea in humans. Foodborne transmission of C. difficile has been suggested as a possible source of human infections, but evidence to confirm this is incomplete.
Listeria are Gram-positive, non-spore forming bacteria, which can be often be found in the environment of farms (Nightingale et al., 2004) and food processing plants (Chasseignaux et al., 2002). There are several species, most of which cause opportunistic infections in humans. The most significant pathogen is L. monocytogenes. Infection by this agent can cause several symptoms including meningitis and endocarditis, and complications of pregnancy (Farber and Peterkin, 1991) L. monocytogenes has been isolated from cattle, sheep, goats and poultry (Gray and Killinger, 1961). A survey performed in the UK in 2003 of 2981 samples of modified-atmosphere-packed and vacuum-packed cooked ready-to-eat meats sold at retail found that 1 % contained L. monocytogenes at levels >102 cfu per gram (Sagoo et al., 2007), and a later UK survey of speciality meats sold at retail found several samples containing similar levels (Gormley et al., 2010).
1.4Other Bacteria
A range of other bacteria found in livestock have the potential for foodborne transmission and are summarised in Table 1.
The spore-forming bacterium Bacillus anthracis, the causative agent of anthrax,commonly infects wild and domesticated herbivorous mammals. The disease is endemic but sporadic in the UK and can be spread by consumption of contaminated meat and meat products. Anthrax spores can survive for very long periods of time in the environment.
Bacillus cereus is a facultative anaerobic bacterium associated with food poisoning in humans. The food poisoning is a result of ingesting heat-stable enterotoxins produced by the bacterium. B. cereus is widespread in the soil and can contaminate such foods as herbs, spices, milk and vegetables. Spores of this organism are heat-resistant and can survive cooking, and a broad range of cooked or processed foods have been associated with infection including vegetables and meats, boiled or fried rice, soups, ice cream, herbs and spices.
Methicillin-resistant S. aureus (MRSA) is recognised as a zoonotic agent following detection in various companion and food-producing animals, including horses, dogs, cats, pigs, cattle, chickens, rabbits and birds. A particular MRSA strain (NT “non-typeable”) has increasingly been isolated from pigs and pig farmers. A recent Dutch study showed that MRSA can be detected at very low concentrations (<10 cfu/g) in unheated meats from various domestic animals and poultry (de Boer et al., 2009). A UK study conducted between 2006 and 2007 (Food Standards Agency Report B18018) indicated that approximately 8 % of red meat produced and sold at retail in the UK was contaminated with S. aureus; no information is available on whether these harboured antibiotic resistance determinants however. Another UK study found MRSA in bulk milk (Garcia-Alvarez et al., 2011).
Mycobacterium bovis is a slow-growing, aerobic bacterium and the causative agent of tuberculosis in cattle (bovine TB). M. bovis may be transmitted to humans via infected milk, although it can also spread via aerosol droplets. Human infections are rare, mostly due to pasteurisation killing any bacteria in infected milk. Cattle are randomly tested for the disease and immediately culled if infected, and depending on the lesions found at meat inspection, the whole carcase is either condemned, or an infected organ or part of the carcase declared unfit for human consumption.
Mycobacterium avium subsp. paratuberculosis is the aetiological agent of ruminant paratuberculosis, commonly referred to as Johne’s disease. The disease is characterised by a chronic granulomatous ileocolitis that ultimately terminates in diarrhoea, weight loss, debilitation, and death. In recent years, there has been an interest in the possible association of paratuberculosis and human Crohn’s disease. M. avium subsp. paratuberculosis may also enter the milk by faecal contamination and is more thermo-tolerant than Mycobacterium bovis and may still remain viable following pasteurisation.
1.5Viruses
There are a number of viruses that are foodborne, or have the potential to be foodborne to humans and also be transmitted to animals. Viral infections are common causes of food poisoning in humans in developed countries. Several major economically important disease outbreaks in livestock, notably Foot and Mouth Disease and Classical Swine Fever, have occurred by feeding food waste containing meat or meat products. The UK operates strict controls over the import of meat and meat products primarily to guard against the introduction of animal diseases. A ban on swill feeding introduced in May 2001 (now included in the Animal By-Products Regulations) was also put into place following the outbreak of FMD in the UK in 2001.
Foot and Mouth Disease (FMD) is an acute infectious disease, causing fever, followed by the development of blisters, chiefly in the mouth and feet cloven-hoofed animals, in particular cattle, sheep, pigs, goats and deer, although other ruminants including deer and camelids can also be affected.
Swine Vesicular Disease, which first occurred in the UK in 1972, has identical symptoms to Foot and Mouth disease. SVD is an acute, contagious viral disease characterized by fever and vesicles with subsequent ulcers in the mouth and on the snout, feet, and teats. The pathogen is relatively resistant to heat, and can persist for a long time in salted, dried, and smoked meat products. The disease can be introduced into a pig herd by feeding food wastecontaining infected meat scraps, by bringing in infected animals, or by direct contact with infected faeces.
Classical swine fever (CSF) is a highly contagious disease of pigs and wild boar. CSF is primarily spread by direct contact or by contact with fomites contaminated with virus. CSF virus can survive in meat and pig products for many months.
African swine fever (ASF) is a serious viral disease of pigs, endemic in Africa. The African swine fever virus (ASFV) is highly contagious, and can spread very rapidly in pig populations by direct or indirect contact.
In poultry several economically important diseases have the potential for foodborne transmission. Newcastle disease (ND) is a contagious disease affecting many domestic and wild avian species. Its effects are most notable in domestic poultry due to their high susceptibility and the potential for severe impacts of an epizootic on the poultry industries. It is endemic to many countries but is absent from the UK. ND is spread primarily through direct contact between healthy birds and the bodily discharges of infected birds. NDV can survive for several weeks on birds' feathers, manure, and other materials and can survive indefinitely in frozen material.
Avian influenza (avian flu or bird flu) refers to influenza caused by viruses adapted to birds. Of the greatest concern is highly pathogenic avian influenza (HPAI). All known viruses that cause influenza in birds belong to the Influenzavirus A genus. All subtypes (but not all strains of all subtypes) of influenza A virus are adapted to birds, although some subtypes are adapted to multiple hosts such that subtypes H7N7 and H5N1 are able to infect humans (Koopmans et al., 2004; Yuen et al., 1998).
The highly pathogenic influenza A virus subtype H5N1 is an emerging avian influenza virus that has been causing global concern as a potential pandemic threat. H5N1 has killed millions of poultry in a growing number of countries throughout Asia, Europe and Africa. Most human infections with avian flu are a result of either handling dead infected birds or from contact with infected fluids. Infectious H5N1 avian influenza virus has been grown from duck meat and the consumption of duck blood has resulted in the infection of humans (Tumpe et al., 2002). This hasraised the question if foodborne introduction could be one of the routes by which new viral diseases can enter the human population, although to date there is no evidence that the AI viruses can be transmitted through poultry products or eggs (
There exists a range of endemic viruses that could potentially spread through the feeding of unprocessed food waste. These are also listed in Table 1, and associated risks are summarised in Table 2.
Rotaviruses infect a variety of animals, including cattle, pigs, sheep, horses, chickens, dogs and cats and there is evidence for zoonotic transmission (Cook et al., 2004). There are a number of various rotavirus antigenic groups (A-G) and serotypes. In calves for example, Group A rotaviruses are the most prevalent in many countries including the UK and are commonly associated with neonatal calf diarrhoea (Bezek 1994). There are few reported outbreaks of foodborne gastroenteritis due to rotaviruses, although it is likely that contamination of foodstuffs can occur.
Hepatitis E virus causes disease in humans and is widespread in Southeast Asia, northern and central Africa, India, and Central America.Reported symptomatic infection is uncommon in the UK and has generally been attributed to acquisition during foreign travel (Sadler et al. 2006), although it is likely that autochthonous infection does occur (Dalton et al., 2008). It is spread mainly through faecal contamination of water and by food. Domestic animals have been reported as a reservoir for the hepatitis E virus, with some surveys showing infection rates exceeding 95% among domestic pigs. Transmission after consumption of wild boar meat and uncooked deer meat has been reported. A link between human hepatitis E cases and hepatitis E virus (HEV) in pig livers, possibly through foodborne transmission of HEV has been suggested(Wichman et al., 2008). HEV has been found in pig populations and in commercial pig livers in several countries; other possible food sources include shellfish (bivalved molluscs). A recent study found HEV in pork sausages sold at retail in the UK (Berto et al., 2012). For taste and other sensory reasons, inadequately cooked pig livers are preferred by some consumers, but the heat treatment thus applied may not be sufficient to inactivate hepatitis E virus. To prevent hepatitis E, food trade and consumers need to cook food thoroughly. Thus for example, with sliced pig liver, depending on thickness and quantity, there is a need to boil at 100°C or stir-fry in hot skillet/wok for at least three to five minutes. Heating to an internal temperature of 90°C for 90 seconds is required for cooking of molluscan shellfish; hence, boil at 100°C until their shells open; boil for additional three to five minutes afterwards. In addition, food trade and consumers are also advised to observe good personal and food hygiene practices. Consumers could ask for thoroughly cooked food when eating out; this is particularly important for high risk populations such as the elderly or pregnant women.
1.6Parasites
Many types of parasites are foodborne, and humans can become infected following the ingestion of infected or contaminated meat, fish, molluscs, vegetables, fruit, or products derived from these foods. In most cases, parasitic infections are acquired by eating raw or incompletely cooked food, or food that is or poorly preserved. Most, if not all, infections are preventable if the food is cooked sufficiently to destroy the infective stages of the parasite.
Meat from many species of animals has been a recognized source of many zoonotic helminth infections but few are likely to pose a risk from recycled food as they will have been identified and removed during meat inspection. A number of foodborne helminth infections have been reported worldwide but have not been recorded in the UK.