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Dr. Dalia El-ShafeiLecturer, Community Medicine Department, Zagazig University

Food born infections

Parasitic infestation

Protozoal infections

Endemic in Egypt & many parts of the world.

Causative Agent: Entamoeba Histolytica, found in 2 phases: Large trophozoite (vegetative form): pathogenic form that invades wall of colon, causing ulcerative lesions. Small trophozoite: commensal in the lumen of large intestine, but potentially pathogenic, and changes under unknown circumstances into the pathogenic large trophozoite.

Infective Stage: Entamoeba cyst:While the vegetative form (large pathogenic trophozoite) is passing with intestinal content toward the rectum, it secretes a cyst wall & develops into a 4-nucleate cyst, the infective stage that passes out with faeces. The cyst is relatively resistant outside the body, but destroyed by heat, desiccation and UV.The vegetative form may pass to the outside with faeces during acute disease, but is delicate and perishes rapidly, and so has no infectious role.

Reservoirs of Infection:1. Man (mainly): chronic cases, or asymptomatic cyst-passers.a) Chronic cases: recovered from acute disease (manifestations disappeared), but infection persists.Acute cases have no infectious role fragile vegetative form perishes rapidly. Even if ingested, it is destroyed by gastric acidity & digestive enzymes of stomach & upper intestine.b) Cyst-passers: asymptomatic, apparently healthy.2. Rats: frequently infected & pass cysts in their excreta.

Modes of Transmission: 1. Food borne infection: ingestion of food or water contaminated with entamoeba cysts, from excreta of man, usually, or may be rats.2. Hand to mouth infection, when hand gets contaminated with cysts: Hand of contacts. From polluted dust, in underdeveloped areas.

Clinical Picture:Incubation Period: commonly 3-4 weeks.

Amoebiasis:clinical involvement of the case by E. histolytica. It may be limited to the colon, giving- intestinal manifestations (1ry amoebiasis), or extend from the colon to other parts of the body (2ry amoebiasis).

Complications:Intestinal amoebiasis: severe amoebic ulceration may cause perforation of colon (& intestinal hemorrhage), and may be peritonitis and appendicitis.Extra Intestinal amoebiasis: amoebic abscesses specially the liver (most frequently affected), amoebic hepatitis.

Diagnosis:Clinical picture may be suggestive. Stools examination: 4-nucleate E. histolytica cysts. Acute cases, however, are difficult to diagnose, as the vegetative form perishes rapidly outside the body.

GIARDIASIS

Causative Agent: Giardia Lamblia intestinal protozoon is found in 2 forms:Trophozoite: inhabits the duodenum and upper intestine, but not invading the tissues.Cyst: the infective stage passed with faeces that can remain viable in the environment for months.

Mode of Transmission:ingestion infection. Food borne infection: ingestion of cysts-contaminated food or water. Hand-to-mouth infection, when hand is contaminated with cysts.

Clinical Picture: A high percent of the infected is asymptomatic. Gastrointestinal manifestations:Giardia is an important causative agent of infective diarrhoeal disease (GE) of infants and young.Diagnosis:stools examined for giardia trophozoite and cysts.

LambliasisAmoebiasisSite Duodenum & upper intestineColonMain C/PEnteritisDysenteryExtra intestinal

Wall invasion

BALANTIDIASIS

Protozoal disease of colon, characterized by dysentery.Causative Agent: Balantidium coli ciliated protozoon. Similar to E.histolytica, 2 forms: trophozoite that inhabits the wall of colon & cyst.Reservoirs of Infection: man, swine.Modes of Infection:Ingestion infection food borne & hand-to-mouth infection

Clinical Picture: Asymptomatic infection. Mild colitis. Acute dysentery.

Untreated cases become chronic.

Helminthes

Prevalence: Worldwide distribution.Preschool & School children are frequently, and may be heavily, infected & may show prevalence of 25% or more in endemic areas.

Causative Agent: Ascaris Lumbricoides a nematode that lives in the lumen of small intestine, with male (15-25 cm) & female (20-40 cm) worms.Reservoir of Infection: infected person. Each female worm puts thousands of eggs every day, to find exit in faeces.Infective Stage: passed eggs are not infective. They develop outside the body in 2-3 weeks, to become embryonated. "Embryonated egg" in polluted environment is the infective stage. It is resistant to desiccation and disinfectants, and remains viable and infective, under favorable environmental conditions, for around 3 months.

Modes of Transmission:Food borne Infection: consuming embryonated egg in contaminated food (salad vegetables) & polluted water.Hand-to-mouth infection: when the hand is contaminated with eggs containing dust. Children are particularly affected, when hands get contaminated on playing in the road, and are infected through either: Putting contaminated fingers in the mouth. Taking food without hand washing.

Predisposing factors: Promiscuous defecation Fresh human fertilizer. Salad (fresh) vegetables without thorough washing. Neglecting care of children who play in the road, and get hands contaminated with Eggs-carrying dust, and not washed.

How Ascaris eggs reach food?Using fresh human fertilizer for vegetables.Contamination of food with eggs-containing dust.Flies may have potential.

Why there is no faeco-oral infection for ascariasis?Because eggs passed in faeces are not infective, except after developing into embryonated egg in 2-3 weeks. That is also why infected food handlers do not spread infection (not directly contaminating food with ascaris eggs).

Incubation Period: about 2 months, from ingestion of embryonated eggs, until eggs first appear in stools.

Clinical Picture:Mild infection may be in apparent.Manifest cases : Respiratory manifestations. Intestinal disorders: abdominal discomfort & colic. Nutritional deficiency: due to anorexia, impaired digestion & protein absorption, loss of nutrients. Others: restless sleep & grinding of teeth, commonly in children.

Diagnosis:C/P is not diagnostic, being not specific, except when adult worms pass & detected in stools. - Identifying the eggs in faeces.

Prevention of Ascariasis:1. Sanitation of environment: Safe water supply, food sanitation. Providing rural areas with sanitary convenient latrines, and sanitary disposal of wastes To be used for fertilization of vegetables, human excreta must be stored, in covered packed heaps, for at least 6 weeks. Fly control. 2. Health education of the public: Using water closet or latrine, and avoid promiscuous defecation. Thorough washing of uncooked (salad) vegetables. Hand washing on returning home, and before food. Supervision of children on playing outdoors, and advise them to avoid putting fingers in the mouth, and wash hands.

Control of Ascariasis:1. Case-finding, on health appraisal: smear of stools is examined for ascaris eggs.2. Cases: treatment, and reexamination to be retreated if necessary.

ENTEROBIASIS(Oxyuriasis pinworm Disease)

Prevalence: The most widespread helminthic infection. Preschool & school children show the highest prevalence

Causative Agent: Enterobius vermicularis, a small roundworm in the caecum & adjacent part of colon and small intestine, and the appendix. Males are few millimeters long, and females around 10 mm long.Reservoir of Infection: the infected person.Infective stage: the egg, almost once deposited by migrating gravid female worm in the perianal region (the worm dies after opposition). Eggs are relatively resistant outside the body.

Modes of Transmission:1. Hand-to-mouth infection: "faeco-oral infection". Autoinfection: fingers and nails of the case get contaminated by scratching the anal region. Hands of contacts may be contaminated with eggs:* Playing with the case.* Handling soiled fomites (e.g. under wears and bedding)* Touching soiled toilet fixtures.2. Ingestion infection: eggs may contaminate food, by either: Handling food by contaminated hand. Eggs-carrying dust in heavily contaminated households.

Clinical Picture: Perianal pruritus & scratching, on migration of gravid female worms and opposition, usually nocturnal, causing disturbed sleep and irritability.

Diagnosis: Worms in perianal region & stools. Perianal swab to demonstrate eggs (using adhesive tape) when necessary. Stool examination is not diagnostic, and so not used, as eggs not necessarily show in stools.

Prevention of Enterobiasis:1. Personal cleanliness: most preventive measure. Keeping hands & nails clean. Nails must also be regularly trimmed.2. Health education of the public, specially parents, for: Clean hands and habits. Supervision of children.3. Food sanitation: clean handling and protection of food.

Control of Cases: Proper antihelminthic therapy. Prevention of autoinfection during treatment, and follow clean habits. Boiling of under wears, clothing and bedding. Guiding cases (and mothers of young children) for: treatment, boiling of fomites, prevention of autoinfection, and protection of family contacts.

TAENIASIS

Taeniasis is an intestinal infection with the adult of large tapeworms.Infectious agent: T.solium (pork tapeworm) & T.saginata (beef tapeworm).Reservoir:Man is the definitive host of both species of taenia. He discharges detached gravid segments which rupture to liberate eggs in human faeces (remain viable for months). Egg is infective to the intermediate host (cattle for T.saginata & pig for T. Solium) where it hatches in the intestine of the animal & the embryo penetrates the intestinal wall & is carried by the circulation to various tissues (especially skeletal muscles where it becomes encysted).

Modes of transmission:Man is infected by ingestion of raw or under cooked infected beef or pork containing the infective stage (cysticercus bovis in beef & cysticercus cellulosa in pork). In the intestine the scolex (in the cysticercus) evaginates, attaches to the mucosa and develops into mature worm.

Occurrence: World wide.The prevalence is high wherever beef or pork are eaten raw or insufficiently cooked and the animal have access to human faeces. Man is usually infected with one worm only.

Period of communicability: so long the worm remains in the intestine sometimes more than 30 ys. T. saginata is not directly transmitted from person to person.

Incubation period:2-3 months from infection to the appearance of eggs in faeces.

Clinical picture:- Many infections are asymptomatic except for the annoyance from having segments of worms emerging from the anus.- Manifestations (if present) include nervousness, insomnia, anorexia, weight loss, however the disease is non fatal.Diagnosis: based on detection of gravid segment or eggs of the worm in faeces.

Methods of control:(1) Preventive measures:a- Health education of the public to:- avoid promiscus defecation to prevent contamination of soil, water and animal food.- cook the meat thoroughly (internal temperature must exceed 60 C) or freeze it below - 5 C for 5 days to kill the infective stage.b. Sanitary raising & feeding of cattle.c. Eliminate source of infection by case finding & treatment.(2) Control measures: Case finding. Specific treatment and reexamination of cases. Specific measures for cases of T. solium as its eggs are immediately infective to man causing cysticercosis to avoid auto &/or contact infection.

N.B: Cysticercosis is a tissue infection with the larval stage of T. solium, where man acts as a definitive and intermediate host. Infection occurs by direct transfer (ingestion) of eggs of T. solium from faeces of infected person to the mouth of the same person (auto infection) or another' s mouth or indirectly through ingestion of contaminated water or food.In the intestine the embryo escapes from the egg shell, penetrates the intestinal wall into lymphatic or blood vessel and is carried to various tissues to produce its manifestations which vary according to the site and intensity. Cerebral involvement is serious with high case fatality. Serologic tests and U.S are diagnostic.

HETEROPHYIASIS

Infectious agents: Heterophyes heterophyes, a minute intestinal trematode, less than 2 mm long that inhabits the small intestine, deeply embedded in the villi.

Infective stage: encysted metacercaria (0.3 mm in diameter), in muscles of infected fish.

Reservoirs of Infection: Man: the infected individuals pass eggs in faeces. Fishermen in endemic areas are particularly important for pollution of brackish water channels where intermediate hosts of the parasite are found. Fish-eating animals (cats & dogs): potential reservoirs.

Mode of Transmission:Ingestion of the infective stage with muscles of infected fish, when eaten raw, or insufficiently cooked or grilled. Ingested cysts excyst in the small intestine, and the liberated metacercariae develop into adult worms, which pass eggs infective to the 1st intermediate host brackish-water snail, pirenella conica, which ingests the eggs that develop into cercariae, and pass them in water. Cercaria found in water pierce the skin of the 2nd intermediate host, Some brackish-water fish (e.g. Mugil cephalus & Tilapia nilotica): to develop and encyst in muscles, forming the infective stage, the "encysted metacercaria".

Occurrence:Heterophyiasis is endemic in Egypt around Lakes Manzala & Borollos where the intermediate hosts of parasite are found, and exposure of the people to infection exists. Other areas may be affected on consuming infected fish. (Salted raw Mugil fish is a popular food, named in Arabic "fessikh". It may transmit infection when eaten before 10 days of pickling).

Clinical Picture: chronic intermittent diarrhea, with blood & mucus in stools, abdominal discomfort and colicky pain.Diagnosis: Examinations of faeces smear for ova. Differential diagnosis: Other causes of dysentery.

Methods of control:(1) Preventive measures:Health education of the public for:- Sufficient cooking or grilling of fish.- Not to consume salted raw fish before 10 days of pickling, to ensure that the metacercariae, if any, are destroyed.(2) Control of cases: -Case-finding and treatment.-Licensing of fishermen after proving to be free of infection & periodic examination. Avoid pollution of water with their excreta (may be practically difficult).

PARASITIC DISEASES TRANSMITTED BY EATING FISH

HYMENOLEPIASIS NANA

Causative Agent: hymenolepis nana (dwarf tapeworm), 25-40 mm long, which inhabits the small intestine. Infective Stage: eggs passed in faeces, are immediately infective.

Reservoirs of Infection: infected man, mainly, and rats, occasionally, where eggs are passed in faeces.

Modes of Transmission:1. Hand-to-mouth infection:- Contaminated hand of the case: may reinfect himself (auto-infection), or infect contacts.- Hand of any person (usually children) may occasionally be contaminated with eggs when playing in rat-execreta-contaminated dirt, and gets infected.2. Ingestion Infection: ingestion of contaminated food and water.3. Internal Autoinfection: ova may not pass in faeces, but invade the intestinal wall and complete their development.

C/P: varies & may be asymptomatic, mild, or vague abdominal disturbance. Heavy infection shows abdominal pain and diarrhea.Diagnosis: examine smear of faeces for ova.

Occurrence: High in underdeveloped communities, specially in preschool and school children, due to poor sanitation (contaminated food, water and soil) and unclean habits.

Methods of control:(A) Preventive measures:1- Sanitation of the Environment:- Sanitary disposal of human excreta.- Food and water sanitation, to prevent pollution with excreta of man and rats.- Rodent eradication or control.2- Health education of the public for clean habits. Children must be supervised during playing outdoors, for clean place & hands.(B) Control of cases and contacts:1- Case-finding: examination of stools on health appraisal, and treatment and re-examination of diagnosed cases.2- Examination of contacts for case -finding.

FASCIOLIASIS

A liver disease caused by a large trematode that is a natural parasite of sheep, cattle and related animals throughout the world.Infectious agents: fasciola hepatica & less commonly F. gigantica. The infective stage is the encysted metacercaria on aquatic plants.Reservoir: sheep (f. hepatica), cattle (f. Gigantica), and other large herbivorous animals. The infection is maintained in a cycle between animals, water, snails and aquatic plants. Man is an accidental host.

Mode of transmission: Infection acquired by eating uncooked aquatic plants such as water cress bearing encysted metacercaria.

Occurrence: world wide especially in sheep or cattle raising areas. F. hepatica is more prevalent in Europe, America, Australia & Middle east. F. gigantica (common in Egypt) has restricted distribution in Africa.

Life cycle:The adult worm lives in liver & bile ducts, eggs pass in the stool, develop in water where it hatch into miracidium snail (lymenoid) where it develops to produce large number of cercaria which attach to and encyst on aquatic plants and when eaten and reach the intestine larva migrate through the wall into peritoneal cavity liver and bile duct. Where it grows and lays eggs.

Period of communicability:Infection is not transmitted directly from person to person.Incubation period: variable.

Clinical picture:Many cases are asymptomatic, right upper quadrant pain & hepatomegally, liver function abnormalities & aesinophilia during liver invasion. D.D other causes of hepatomegally.After migration to biliary ducts the worm may cause biliary colic or obstructive jaundice.

Diagnosis:Based on finding characteristic eggs in faeces or in bile aspirated from the duodenum.

N.B: detection of non viable eggs in the faeces occurs after eating liver from infected animal.

Methods of control:A-preventive measures:- Educate the public in endemic areas to abstain from eating aquatic plants.- Avoid use of sheep or cattle faeces for fertilizing water plants.- snail control when feasible.- Mass treatment of infected animals.B -Control of patient: by early diagnosis and treatment.

HYDATID (Hydatidosis)

Causative Agent: Hydatid cyst, which is the larval (intermediate) stage of Echinococcus granulosus of dog. The cyst affects different organs of man.

Reservoir of Infection:The dog is the definitive host of Echinococcus granulosus, 3 small tapeworm, some millimeters long, in the small intestine. Eggs pass in the faeces of dog.

Intermediate Host:Sheep, cattle and other herbivorous animals. They ingest Echinococcus egg-contaminated food, to form hydatid cysts in different animal organs, specially the lung & liver. The dog gets infected with the worm on ingesting hydatid cyst in animal organs, and the cycle of dog-animal-dog infection continues.

Infection of Man: Man may occasionally be infected with Echinococcus eggs from dogs, and gets affected with hydatid cyst.

How man gets infected with eggs: Hand-to-mouth infection: the usual method of infection, when the hand gets contaminated with eggs, from contact and playing with infected dogs. Food-borne infection: ingestion of food or water which has been accidentally contaminated with excreta of infected dogs.

C/P: no specific picture, but manifestations of slowly growing tumor, according to location of hydatid cyst.

Diagnosis: Clinical examination: cystic tumor, which is nonspecific & not diagnostic, but suggestive. X-ray: supports suspected disease, but not conclusive. Biopsy or aspiration of cyst: is avoided, for the risk of anaphylaxis and 2ry infection. Casoni test: ID hypersensitivity test. +ve reaction is diagnostic.

Prevention:1- Measures for Dogs:. Prevention of infection: abattoirs must be free of dogs & affected part(s) of slaughtered animals must be burnt. . Elimination of stray dogs, and licensing of the others after examination for Echinococcus and treatment of the infected. 2- Protection of Man:. Personal cleanliness: avoiding contact with suspected dogs, and keeping the hands clean.. Supervision of children, as they usually like to play with dogs. . Food and water sanitation.