FOOD BORNE DISEASES
Foodborne diseases are illnesses that result from ingestion of contaminated food. More than 250 different foodborne hazards have been recognized including infectious bacteria, viruses and parasites, and noninfectious chemicals and toxins. Many of these agents commonly cause diarrhea and vomiting, but there is no single clinical syndrome for all foodborne diseases. The sources of these agents range from being an inherent constituent of the food to inadvertent (or intentional) addition during food production, processing, or preparation. Moreover, most foodborne agents can be transmitted via routes other than food, including through water or through contact with infected farm animals, pets, and humans. The proportion of disease associated with being foodborne will differ depending on the agent and food handling, with only a few foodborne diseases being transmitted exclusively via foods eg Listeria monocytogenes whereas Escherichia coli O157:H7 infections can be acquired by ingesting contaminated food or water or by direct contact with infected animals or persons.
Determining whether an illness is foodborne can be difficult because the illness may not develop for days or even weeks after exposure to a pathogen, and the most recently eaten meal may incorrectly get the blame. One way to determine that a disease is foodborne is to find the agent that caused the disease in a sample of the food that the ill person has eaten. This is not always possible because leftover food may not be available or no analytical technique may exist to detect the agent. Another way to determine that a disease is foodborne is when a cluster of cases of an illness occur among persons who had nothing else in common other than having eaten the same food; such clusters are sometimes defined, in recent years, by “molecular fingerprinting” of agents isolated from cases spread over a wide geographic area.
Food poisoning, also called food intoxication, is disease that results from ingestion of foods containing preformed microbial toxins. The microorganisms that produced the toxins do not have to grow in the host and are often not alive at the time the contaminated food is consumed. The illness results from the ingestion and action of a bioactive toxin.
By contrast to food poisoning, food infection is a microbial infection resulting from the ingestion of pathogen- contaminated food followed by growth of the pathogen in the host.
MICROBIAL SAMPLING FOR FOODBORN DISEASE
In addition to non pathogenic microorganisms, pathogenic micro organisms may be present in fresh foods. Rapid diagnostic methods that do not require pathogen growth or culture have been developed to detect impt food pathogens such as Escherichia coli O157:H7, Salmonella, Staphylococcus and Clostridium botulinum. Molecular and immunology based tests are used to identify both toxin and pathogen contamination of foods and other products such as drugs & consmetics. The presence of a foodborne pathogen or toxin, however, may not be sufficient to link particular foods or pathogens to specific foodborne disease outbreak. The causal organism should be isolated and identified to complete investigation of foodborne illness outbreaks. Isolation & growth of pathogens from non-liquid foods usually requires preliminary treatment to suspend micro organisms embedded or entrapped within the food (using–blender- stomacher).
Examination within 1 hour of sampling or refrigerated if analysis will not be done immediately.
Food samples can be inoculated onto enriched media, followed by transfer to differential or selective media for isolation & identification. Final identification of food borne pathogens by growth characteristics as well as the use of molecular and genetic methods such as PCR, nucleic acid probes, nucleic acid sequencing, and ribotyping may be used to link specific organisms to foodborne diseases.
Tracking the characteristics of foodborne illnesses and identifying the causative agents often allow epidemiologists to pinpoint the common source of contaminated food.
STAPHYLOCOCCAL FOOD POISONING
Food poisoning is often caused by toxins produced by the bacterium Staphylococcus aureus. Staph spp. is small gram +ve cocci. They are normal members of the local flora of the skin & upper respiratory tract of nearly all humans and often opportunistic pathogens. S. aureus is frequently associated with food poisoning because it can grow in many common foods, and some stains produce several heat stable enterotoxins produce. If the toxin is consumed in food, gastroenteristis xterized by nausea, vomiting, and diarrhea, occurs within 1-6 hours.
Epidermiology
The foods most commonly involved are custard and cream filled baked goods, poultry, meat and meat products, egg & meat salads, puddings & creamy salad dressings.
Diagnosis-
detection of enterotoxin (ELISA) or S. aureus exonuclase to determine metabolite in foods immediately after preparation, they remain safe because S.aureus grows poorly at low temps. However, foods of this type are often kept at room temp in kitchens or outdoors at picnics
Infected food handlers may harbor live S. aureus and infect foods causing illness,
the illness is solely due to the preformed toxin
The symptoms of S aureus food poisoning can be quite severe but are typically self-limiting usually resolving within 48hrs as the toxin is shed from the body. Severe cases may req treatment for dehydration. Treatment with antibiotic is not useful.
Prevention
Is by proper sanitation &hygiene in food production, food preparation & food storage. As a rule, food susceptible to colonization by S aureus and kept for several hours at temp above 40c should be discarded rather than eaten
CLOSTRIDIAL FOOD POISONING
Clostridium perfringers and Clostridium botulinum cause serious food poisoning. Member of the genus Clostridium are anaerobic endospore forming rods. Under appropriate anaerobic conditions, the endorspores can then germinate and toxin is produced.
C.perfringes is an anaerobic, gram-ve endospore forming rods. canning and cooking procedures kill living organisms but do not necessarily kill endospores. Under appropriate anaerobic conditions, the endospores can then germinate and toxin is produced.
Clostridium perfringens food poisoining. is an anaerobic gram-+ve endospore forming rod commonly found in soil. It also lives in small nos in the intestinal tract of many animals and humans and is therefore found in sewage.
Perfrigens food poisoning req the ingestion of a large dose of C.perfrigens in contaminated cooked or uncooked foods, esp high protein foods such as meat, poultry and fish. After consumption of the contaminated foods, the living c
C. perfrigens begin to sporulate in the intestine, which concedes with the products of the perfrigens enterotoxin. When ingested, perfrigens enterotoxin alters the permeability of the intestinal epithelium, leading to nausea, diarrhea and intestinal gramps usually with no fever. Onset begins about 7-15hrs after consumption of the contamninated food but usually resolves within 24hrs and fatalities are rear.
Diagnosis ,treatment and prevention.
Diagnosis of perfrigens food poisoning is made by isolation of C. perf from the feces or more reliably by a direct enzymes linked immunosorbent assay (ELISA) to detect C. perf enterotoxinin feces. Because the disease is self limiting, antibiotic treatment is not indicated. Prevention of perf food poisoning requires measures to prevent contamination of raw and cooked foods and control of cooking and canning procedures to ensure proper heat treatment of all foods. Cooked foods should be refrigerated as soon as possible to rapidly lower temp and inhibit c. perf growth.
BOTULISM
This is a severe, often fatal, food poisoning that occurs following the consumption of food containing the exotoxin produced by C. botulinum. The bacterium normally inhabits soil or water, but its endospores may contaminate raw foods before harvest or slaughter. If the foods are properly processed so that the C botulinum endospores are removed or killed, no problem arises, but if viable endospores are present, they may germinate & produce toxin. Even a small amount of the resultant neurotoxin can be dangerous. Botulinum toxin is a neutotoxin that causes flaccid paralysis, usually affecting the autonomic nerves that control body functions such as respiration and heartbeat. Because the toxins are destroyed by heat (80oC for 10 mins), thoroughly cooked food, even if contaminated with toxin, can be totally harmless. Eg canned vegetables (Corn & beans)
Infant botulism occurs when neomates ingest endospores of C botulinum. (Raw honey is the vehicle) 1 st week- 2 months old. Don't give honey to children under 2 years
Wound botulism is most commonly associated with illicit injectable drug use. Diagnosis, treatment & prevention
Diagnosis of botulium is by demonstrating botulinum toxin in patient serum or by finding toxin or live C. botulinum in suspected food products. Clinical observation including neurological signs of logicalized paralysis (impaired vision & speech) beginning 18-29hrs after ingestion of contaminated food.
Treatment involves administration of botulinum antitoxin if the diagnosis is early, mechanical ventilation for flaccid respiratory paralysis.
Prevention of botulism reqs maintaining careful controls over canning & preservation methods. "Food can be heated to destroy endospores, boiling for 20 min destroy the toxin.
FOOD INFECTION
Food infection results from ingestion of food containing sufficient nos. of viable pathogens to cause infection and disease in the host.
SALMONETHOSIS
Salmonellosis is a gastrointestinal disease typically caused by food borne salmonella infection. Symptoms begin after the pathogen colonizes the intestinal epithelium. Salmonella are gram- negative facultatively aerobic motile rods related to Esherichia coli and other enteric bacteria. It normally inhabits the animal intestine and is thus found in sewage Salmonella typhimurium and Salmonella enteritidis serotypes most commonly cause of foodborne salmonellosis in humans.
EPIDERMIOLOGY
The organism may reach food by fecal contamination form food handlers, food production animals such as chicken, pigs & cattle may also harbor salmonella serotypes that are pathogenic to humans & may pass the bacteria to finished fresh foods such as eggs, meat & dairy products, cream cakes, pies, custards made with uncooked eggs. Meat, meat products eg meat pie, cured by cooked sausages and poultry, milk & milk products are also commonly implicated. Incubation period is 1-2 weeks/ between 8 - 48 hours after ingestion. Symptoms include the sudden onset of headache, chills, vomiting & diarrhea, followed by a fever that lasts a few days. Few serotypes of salmonella may cause septicemia (blood infection) and enteric or typhoid fever, disease xterized by systemic infection and high fever lasting several weeks ( 3-4 weeks).
Diagnosis, treatment, & prevention
Diagnosis of food borne salmonellosis is made by observation of clinical symptoms, history of recent food consumption, and by culture of the organism from feces.
For enterocolitis, treatment is usually unnecessary and antibiotic treatment does not shorten the course of the disease or eliminate the carrier state. Antibiotic treatment, however significantly reduces the length & severity of septicemia and typhoid fever. Properly cooked foods heated to at least 70oC for 10 min are generally safe if consumed immediately held at 50oC, or stored immediately at 4oC. Salmonella infections are more common in summer than in winter, probably because warm environmental conditions generally favor the growth for microorganisms in foods.
The pathogenesis of salmonella infections starts with uptake of the organisms from the gut. salmonella ingested in food or water invades phagocytes and grows as an intracellular pathogen, spreading to adjacent cells while host cell die. After invasion, pathogenic salmonella uses a combination of endotoxin, enterotoxin & cytotoxin to damage and kill host cells, leading to the classic symptoms of salmonellosis
PATHOGENIC ESCHERICHIA COLI
Most stains of E. coli are not pathogenic .They are common members of the enteric microflora in the human colon. A few strains, however, are potential food borne pathogens. All pathogenic strains are intestinal pathogens and several are characterized by their ability to produce potent enterotoxins. Several cause life- threatening diarrheal disease and UTIs. The pathogenic strains are divided into categories based on the type of toxin they produce & the specific disease the cause.
ENTEROHEMORRHAGIC ESCHERICHIA COLI (EHEC)
EHEC produce verotoxin, and enterotoxin similar to one produced by shigella dysenterieae the shiga toxin. After a person ingests food or water containing one well-known EHC strain.
E coli 0157:H7, the organisms grows in the small intestine & produces verotoxin. This pathogen is the leading cause of hemolytic uremic syndrome and kidney failure. The most common cause of this infection is the consumption of contaminated cooked or under cooked meat, particularly mass-processed ground meat.E coli 0157:H7 has also been implicated in food infection outbreaks from dairy products, fresh fruit foods by fecal material/ typically from cattle carrying the E coli 0157 ; H7 strain has been implicated in several cases .
Other pathogenic Escherichia coli common in children in developing countries often contract diarrheal disease caused by E. coli. It can also be the cause of "traveler's diarrhea", an extremely common enteric infection causing watery diarrhea in travelers to developing watery diarrhea in travelers to developing countries.
The causal agents are the enterotoxigenic E. coli (Etec). The strains usually produce one of two heat-laible diarrhea producing enterotoxins. The prime vehicles are foods such as fresh vegetables and water.
Enteropathagenic E coli (Epec) strains cause diarrheal diseases in infants and small children .
invasive E.coli (EIEC) stains cause invasive disease in the colon, producing watery sometimes bloody diarrhea.
Diagnosis treatment & prevention
lab diagnosis reqs culture from the feces and identification of the O (Lipoplysacchande) and H (flagellar) antigens and toxins by serology.
Treatment involves supportive therapy, antimicrobial drugs to shorten & eliminate infection. Proper food handling, water purification, and appropriate hygiene prevent the spread of pathogenic E coli. Make sure meat is thoroughly cooked.
OTHER FOOD BORN INFECTIOUS DISEASES
Yersinia enterocolitica is commonly found in the intestines of domestic animals and causes foodborne infections due to contaminated meat and dairy products. The most serious consequence of Y. enterocolitica infection is enteric fever, a severe life- threatening infection.
Bacillus cereus produces two enterotoxins that cause diarrhea and vomiting. The organism grows in foods that are cooked and left to cool slowly at room temp. such as rice, pasta, meats or sauces.
Shigella spp cause nearly 100,000 cases of severe foodborne invasive gastroenteritis called shigellosis each year.
Several members of the vibrio genus cause food poisoning in persons who consume contaminated shellfish.
Viral foodborne illness consists of gastroenteritis characterized by diarrhea, often accompanied by nausea & vomiting. Recovery is rapid and spontaneous, usually within 24-48hrs. Rotavirus, and hepatitis A collectively cause 100,000 cases of foodborne disease each year.These viruses inhabit the gut and are often transmitted to food or water with fecal matter. Proper food handling, handwashing and a source of clean water to prepare fresh foods are essential to prevent infection. Protists including Giardia lamblia, Cryptosporidium parvum and Cyclospora cayetanen can spread in foods contaminated by fecal matter in untreated water used to wash, irrigate, or spray crops. Fresh foods such as fruits are often implicated as the source of these protists.
Cyclosporiasis is an acute gastroenteritis and is an important emerging disease. In the United States, most cases are acquired by eating fresh produce imported from other countries.
Toxoplasma gondii is a protest spread through cat feces, but is also found in raw or under cooked meat. In most individuals it is a mild, self-limiting gastroenteritis. However, prenatal infection can lead to serious acute toxoplasmosis resulting in tissue involvement, cyst formation and complications such as myocarditis, blindness and still birth in the fetus. Immunocompromised individual such as AIDs patients may develop acute toxoplasmosis. Toxoplasma infections in compromised hosts can be treated with the antiprotist drug.