Alimentary Infections

These infectious agents enter the human body through the digestive tract. They are caused by the consumption of contaminated food with infectious agents, which leads to food poisoning. These infections lead to gastroenteritis that typically involves diarrhoea, vomiting, and abdominal cramps. These symptoms usually begin 12–72 hours after contracting the infectious agent and if due to viral agent usually lasts less than one week. Some viral causes may also be associated with fever, fatigue, headaches, and muscle pains. If the stool is bloody the cause is less likely to be viral and more likely to be bacterial. Some bacterial infections may be associated with severe abdominal pain and may last for weeks without treatment.

=Aetiology=

a) Typhoid fever
This is a systemic disease transmitted by the ingestion of food or water contaminated with the faeces of an infected person, the aetiological agents is Salmonella typhi, and man is the reservoir. The clinical features are characterized by a slowly progressive fever as high as 40 °C, profuse sweating and gastroenteritis. Less commonly, a rash of flat, rose-colored spots may appear. Its occurance is worldwide,and multi-drug resistant strains have been reported from asia, middle east and latin America. Sanitation and hygiene are the critical measures that can be taken to prevent typhoid. Typhoid does not affect animals and therefore transmission is only from human to human. Typhoid can only spread in environments where human feces or urine are able to come into contact with food or drinking water. Careful food preparation and washing of hands are crucial to preventing typhoid.

b) Salmonellosis
Aetiological agent is numerous serotypes of salmonella. In most countries which maintain salmonella surveillance. S.Typhimurium and S.Enteritidis are two most commonly reported. The reservoir is domestic and wild animals including poultry also humans ie patients, carriers. The mode of transmission is by ingestion of the organism in food derived from infected food animals or contaminated by faeces of infected animal or person. This includes raw and undercooked eggs and egg products, raw milk and raw milk products, meat and meat products,poultry andpoultry products. Its occurrence is worldwide and more extensively reported in north America and Europe.

c) Shigellosis
Aetiological agent is four species of genus shigella. S.dysenteriae, S.flexneri, S.bodii, S.sonnei, with man being the reservoir. These organisms invade the superficial colonic mucosa causing inflammation. Local multiplication and invasion is possible via a virulence factor, together with the production of a toxin. A cholera‐like presentation may occur if the disease is due to S. dysenteriae, which produces a cytotoxin, Shiga toxin. Some 50% of cases occur in children less than10 years old due to the fact that faecal‐oral route is needed.

d) Cholera
Cholera is an acute infectious disease endemic and epidemic in Asia. It is caused by Vibrio cholerae in two biotypes ‐ classic and El Tor. The latter is able to survive longer in nature, can cause sub-clinical cases. It has a longer faecal excretion of the organism, and can be transmitted from case to case or via food and water. El tor has caused outbreaks or epidemics in Portugal and Italy. Transmission of cholera has been linked to contaminated drinking water drawn from shallow unprotected wells and also bottled water with ice. Seafood has frequently been a source of cholera especially undercooked or raw shellfish. Most people infected with V. cholerae tend to have mild‐to‐moderate diarrhoea. However, if left untreated, cholera can be one of the most rapidly fatal infectious illnesses known. In endemic areas the incidence of cholera is highest in children, the incidence tends to decrease with age due to acquired immunity

e) Campylobacteriosis
Campylobacter jejuni food poisoning is characterised by a prodromal malaise, abdominal pain, diarrhoea, with vomiting being uncommon. The problems are due to multiplication of the organisms within the gut and the release of endotoxin, with symptoms occurring after 2 to 5 days. It was the most common cause of gastroenteritis in England and Wales in 1991. The organism comes from poultry and unpasteurised milk. Animal is the reservoir. Causes 5‐14% of diarrhoea worldwide.

f) others
Staphylococcal food poisoning, Clostridium perfringens food poisoning, Bacillus cereus food poisoning and Botulism are also infecting gastrointestinal tract and through their toxins cause gastroenteritis.

a) Rotaviral Enteritis
Rotavirus gastroenteritis is an important cause of diarrhoea and vomiting in children, affecting boys more often than girls. It is the most common cause of gastroenteritis in children, but is not a notifiable illness and therefore not recorded as frequently as bacterial gastroenteritis. There are winter and spring peaks, which fall off in the summer. Usually the patient is less than one year old, rotavirus is only seen in the under fives and in the elderly. Transmission is by faecal oral route, and the reservoir is man.

b) Norwalk type disease
Norwalk virus named after the city in Ohio where the first identified outbreak occurred. Virus is shed in vomitus and faeces. Transmission is via faecal‐oral route via contaminated food, waterand infected contacts. Reservoir is man.

c) Viral Hepatitis A
Hepatitis A virus hepatitis accounts for 20‐25% of clinical hepatitis worldwide. It is due to a small, single stranded RNA picornavirus. HAV hepatitis may be referred to as infectious hepatitis. The reservoir is man. HAV is spread by the faeco‐oral route. Parenteral spread may very rarely follow transfusion of blood from a donor who is in the incubation stage of the disease. Children of school age are most often affected. Adults are usually infected by spread from children. There are about 7000 cases of HAV per year in the UK, 15% of cases are associated with foreign travel of which 50% were associated with travel to the Indian subcontinent,3% implicate food contamination most commonly shellfish Epidemics may occur, usually associated with water or food contamination. Vaccination or passive immunisation with immune serum globulin is recommended for travellers to highly endemic areas and to close personal contacts of sufferers.

d) Hepatitis E
‐ Hepatitis E virus accounts for sporadic and major epidemics of viral hepatitis in developing countries, particularly, SE Asia, Nepal, Algeria, Japan, Siberia, Mongolia, and in traveller's returning from these areas. Transmission is by the faeco‐oral route, usually by contaminated sewage water and the reservoir is man.

e) Poliomyelitis
Poliomyelitis is a notifiable infectious viral illness affecting the central nervous system. Poliomyelitis is an acute illness that follows invasion through the gastrointestinal tract by one of the three serotypes of polio virus (serotypes 1, 2 and 3). The polio virus replicates in the gut and has a high affinity for nervous tissue. Most often the infection is clinically inapparent, or symptoms may range in severity from a fever to aseptic meningitis or paralysis. Headache, gastrointestinal disturbance, malaise and stiffness of the neck and back, with or without paralysis, may occur. Transmission is through contact with the faeces or pharyngeal secretions of an infected person. When the infection is endemic, the paralytic disease is caused by naturally occurring poliovirus wild virus and the reservoir is man.

3. Parasites
They populate the gastrointestinal tract in humans and other animals. They can live throughout the body, but most prefer the intestinal wall. The major groups of parasites include protozoans and parasitic worms (helminths). Of these, protozoans, including cryptosporidium, microsporidia, and isospora, are most common in HIV-infected persons. Each of these parasites can infect the digestive tract, and sometimes two or more can cause infection at the same time. Parasites can get into the intestine by going through the mouth from uncooked or unwashed food, contaminated water or hands, or by skin contact with larva infected soil. When the organisms are swallowed, they move into the intestine, where they can reproduce and cause symptoms. Children are particularly susceptible if they are not thoroughly sterilized after coming into contact with infected soil that is present in environments that they may frequently visit such as sandboxes and school playgrounds. People in developing countries are also at particular risk due to drinking water from sources that may be contaminated with parasites that colonise the gastrointestinal tract.