食品安全监管食品安全 (4).pdf

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1、Food hazards from emerging pathogens What are emerging pathogens?What actions can be taken to stop risks to food from emerging pathogens?Professor Nimal Pathiraja,PhD-U of Edinburgh What are emerging pathogens 2 Emerging,or in some cases re-emerging,food-borne problems are commonly considered to be

2、those problems that have recently appeared in a population;have extended to new vehicles of transmission;have started to increase rapidly,in incidence or geographic range;have various causes(e.g.ecological,environmental,food production or demographic factors);and have been widespread for many years

3、but only recently identified because of new or increased knowledge or methods of identification and analysis of the disease agent.What are emerging pathogens 3 They can be newly-discovered,linked for the first time to disease in humans or to a particular food.A pathogen may also be defined as emergi

4、ng when significant new strains emerge from an existing pathogen,or if the incidence of a pathogen increases dramatically What factors affect their emergence Changes in the pathogens.Microbial adaptation through natural selection is a key process in the emergence of pathogens.The therapeutic use of

5、an antimicrobial agent in human or animal populations creates a selective pressure that favours survival of bacterial strains resistant to the agent.Economic and technical developments have introduced new foods.New production systems or environmental changes increase access to certain foods.The food

6、 chain has become longer and more complex,thus increasing opportunities for contamination.Poverty and pollution.Dietary habits.Travel and migration Trade in food,animal feed and animals.Globalization,New food vehicles of transmission 4 Emerging bacteria Escherichia coli O157.Referred to as enterohae

7、morrhagic E.coli(EHEC),this pathogen produces toxins known as verotoxins.Cattle appear to be the main reservoir.Transmission to humans is principally through the consumption of contaminated foods,such as raw or undercooked meat products and raw milk.Fresh-pressed apple juice or cider,yoghurt,cheese,

8、salad vegetables and cooked maize have also been implicated.Faecal contamination of water and foods,as well as cross-contamination during food preparation,can lead to infection,as can person-to-person contact.It is a major cause of bloody and non-bloody diarrhoea and often leads to long-term complic

9、ations such as haemolytic uraemic syndrome.5 Enteroaggregative E.coli(EAEC)6 Enteroaggregative E.coli(EAEC)has increasingly been recognized as an agent of a watery mucoid diarrhoea especially in children.It is particularly associated with persistent diarrhoea(lasting for more than 14 days),a major c

10、ause of illness and death.It is thought that EAEC adheres to the intestinal mucosa and elaborates enterotoxins and cytotoxins,which result in secretory diarrhoea and mucosal damage.Recent studies support the association of EAEC with malnutrition and growth retardation in the absence of diarrhoea.Lis

11、teria monocytogenese 7 This ubiquitous microorganism has been isolated from various environments,including decaying vegetation,soil,animal feed,sewage and water.It is resistant to diverse environmental conditions and can grow at temperatures as low as 3C.It is found in a wide variety of raw and proc

12、essed foods such as milk and cheeses,meat(including poultry)and meat products,and seafood and fish products where it can survive and multiply rapidly during storage.L.monocytogenes is responsible for opportunistic infections,preferentially affecting individuals whose immune system is weak,including

13、pregnant women,newborn babies and the elderly.It primarily causes meningitis,encephalitis or septicaemia and,when pregnant women are infected,it can lead to abortion,stillbirth or premature birth.Multidrug-resistant Salmonella typhimurium DT 104.8 This microorganism has been isolated from cattle,pou

14、ltry,sheep,pigs and horses.Antimicrobial therapy is used extensively to combat S.typhimurium infection in animals,and the evolution of a strain resistant to the commonly used antibiotics has made infections with S.typhimurium in food animals difficult to control.The primary route by which humans acq

15、uire infection is through the consumption of a large range of contaminated foods of animal origin.Salmonella enteritidis This bacterium is the dominant cause of human salmonellosis in many parts of the world.Poultry,eggs and egg products,in particular,are contaminated,but the microorganism has also

16、been found in other foodstuffs such as ice cream.Cross-contamination,undercooking and inadequate cooling procedures promote the spread and growth of salmonella during processing and handling.One important characteristic of S.enteritidis is its ability to contaminate the contents of intact egg shells

17、.Manifestation of illness includes invasive disease and reactive arthritis.9 Campylobacter jejuni 10.Most sporadic infections with this pathogen are associated with improper preparation or consumption of mishandled poultry products.Most C.jejuni outbreaks,which are far less common than sporadic illn

18、esses,are associated with the consumption of raw milk or unchlorinated water.The reservoirs of this organism include poultry,cattle,swine,sheep,rodents and birds.Vibrio vulnificus The consumption of raw molluscan shellfish that are contaminated with this microorganism,which is a normal inhabitant of

19、 some marine environments,often leads to primary septicemia and death.Individuals most susceptible to infection with this agent include those with chronic liver disease or chronic alcoholism,or those who are immunosuppressed in some way.11 BSE-Prions mad cow disease 12 Transmissible spongiform encep

20、halopathies in animals and humans are caused by an unconventional virus or prion.These conditions include scrapie in sheep,bovine spongiform encephalopathy(BSE or mad cow disease)in cattle and Creutzfeldt Jacob disease(CJD)in humans.It is commonly accepted that BSE was first caused in the United Kin

21、gdom when cattle were fed carcass meal from scrapie-infected sheep.It is also accepted that humans contracted the non-classic form of CJD after consuming cattle meat,in particular nerve tissue 13 Severe acute respiratory syndrome(SARS)1.SARS is a viral respiratory disease of zoonotic origin caused b

22、y the SARS coronavirus(SARS-CoV).2.Between November 2002 and July 2003,an outbreak of SARS led to 8,096 cases and 774 deaths reported in multiple countries with the majority of cases in Hong Kong(9.6%fatality rate)according to the World Health Organization(WHO).3.Within weeks,SARS spread from Hong K

23、ong to infect individuals in 37 countries in early 2003 Viral diseases Many new virus that can be associated with food 1.MERS 2.Avian flu 3.Hepatitis E etc.14 15 Middle East Respiratory Syndrome(MERS)1.MERS is a viral respiratory illness that is new to humans.It was first reported in Saudi Arabia in

24、 2012 and has since spread to several other countries,including the United States.Most people infected with MERS-CoV developed severe acute respiratory illness,including fever,cough,and shortness of breath.Many of them have died.2.Scientists have described the isolation and sequencing of Middle East

25、 respiratory syndrome coronavirus obtained from a dromedary camel and from a patient who died of laboratory-confirmed MERS.16 Camel meat and milk 17 Hepatitis E virus infection(HEV)1.Hepatitis E virus is one of a number of viruses that can cause viral hepatitis in humans 2.Hepatitis E is the inflamm

26、ation of liver caused by HEV.3.The disease is generally self-limiting and resolves within two weeks;4.The virus usually causes only relatively mild symptoms such as sickness,a temperature and muscle pain,malaise,anorexia,nausea,abdominal pain,dark urine and jaundice which clear up within a month.18

27、Hepatitis E virus(HEV)in pigs It remains endemic in pigs in many parts of the Far East and Africa.It is also common in some part of Southeast Asia.In some countries,around 80 85%of pigs carry the virus 19 Hepatitis E virus infection(HEV)1.However,in some countries there has been an increase in the n

28、umber of human cases not related to travel to endemic countries.2.It is not known whether these cases were caused by inadequately cooked food such as shellfish and pig offal which are documented as possible food sources 3.Bivalve shellfish,which feeds by filtering out the seawater,tends to concentra

29、te viruses,including HEV,present in the polluted waters 20 Hepatitis E virus(HEV)Hepatitis E is commonly associated with contaminated drinking water but is increasingly becoming linked with pork in many countries.HEV has been found in pig populations across the world and in commercial pig livers in

30、Japan,United States,Hong Kong and Netherlands.Genetic homology,i.e.same gene partial sequences,was identified between some HEV isolates from pigs and human cases.21 Pig liver can be a source HEV 1.Pig liver should be cooked well,including the deeper areas 2.Lightly cooked pig livers are preferred by

31、 some consumers 3.Slice raw meat and offal into thin strips to allow thorough cooking in special food types How to control emerging pathogens The key to manage the risks from them are:1.Understand the characteristics of the pathogens 2.Understand the their occurrence and epidemiology 3.Use risk assessment with available data 4.Use science-based methods to control the hazards such as HACCP 22