COMMUNICABLE DISEASES : INFECTIONS THROUGH THE GASTRO-INTESTINAL TRACT

1. COMMUNICABLE DISEASES:INFECTIONS THROUGH THEGASTRO-INTESTINAL TRACT Dr. MayssaaEssam

2. HEAD LINES ■Infective agents ■ Control of the infections acquired through the gastro-intestinal tract ■ Diarrhoeal diseases ■ Viral infections ■ Bacterial infections ■ Protozoal infections ■ Helminthic infections

3. INFECTIVE AGENTS A number of important pathogens gain entry through the gastro-intestinal tract. Some of these cause diarrhoeal diseases (e.g. Salmonella and Shigella spp.) whilst others pass through the intestinal tract to cause disease in other organs (e.g. poliomyelitis, viral hepatitis). The pathogens include viruses, bacteria, protozoa and helminths. • Viral infections :Poliomyelitis (poliovirus) • Viral hepatitis (hepatitis A and E viruses) • Bacterial infections • Enteric fevers (Salmonella typhi, S. paratyphi) • Gastro-enteritis (Escherichia coli, Campylobacter spp.) • Protozoal infections • Amoebiasis (Entamoeba histolytica) • Giardiasis (Giardia lamblia) • Helminthic infections • Nematodes(roundworms) • Cestodes (tapeworms) • Trematodes (flukes)

4. PHYSICAL AND BIOLOGICAL CHARACTERISTICS The epidemiology of these infections, it is useful to note some of the physical and biological properties of each infective agent. The organisms vary in their ability to withstand physical conditions such as high or low temperatures and drying, and they also differ in their susceptibility to chemical agents, including chlorine. The vegetative form ?of Entamoeba histolytica is rapidly destroyed in the stomach but the cyst form? survives digestion by gastric juices. Differences in the sizes of the organisms are also of epidemiological importance. Thus, simple filtration through a clay filter will eliminate most of the large organisms – bacteria, protozoa, and the eggs or larvae of helminths – from polluted water, but the filtrate will contain the smaller organisms such as viruses.

5. TRANSMISSION Viruses, bacteria and cysts of protozoa are directly infectious to man as they are passed in the faeces, butin the case of helminths, the egg may become infectious only after maturation in the soil (e.g. Ascaris) or after passing through an intermediate host(e.g. Taeniasaginata). The most important pattern of transmission is the passage of infective material from human faeces into the mouth of a new host and this is known as ‘faeco-oral’ or ‘intestino-oral’ transmission,not all the pathogens which infect through the mouth are excreted in the faeces; for example guinea worm infection is acquired by mouth but the larvae escape through the skin. On the other hand, the ova of hookworm are passed in faeces but the route of infection is most frequently by direct penetration of the skin by the infective larvae.

6. The faeco-oral route Faeco-oral transmission occurs mostly through inapparent faecal contamination of food, water and hands – the three main items that regularly make contact with the mouth It should be noted that minute quantities of faeces can carry the infective dose of various pathogens. Thus, dangerously polluted water may appear sparkling clear, contaminated food may be free of objectionable odour or taste, and apparently clean hands may carry and transmit disease. The housefly mechanically transfers faecal pollution by: ■ Carrying faeces on its hairy limbs ■ Regurgitating the contents of its stomach on to solid food as a means of liquefying it (‘vomit drop’); ■ Defecating on the food: its faeces may contain surviving organisms derived from human faeces.

7. As shown in Figure below, food occupies a central and important position. Not only can it be contaminated directly by faeces but it can also be contaminated indirectly through polluted water, dirty hands, contaminated soil and filth flies. Water may be polluted directly by faeces but also indirectly from the polluted soil on the riverbank. There are many opportunities for the contamination of hands: the person may contaminate hands on cleaning after defaecation or in touching or handling contaminated objects, including soil. Contamination of the soil with faeces plays an essential role in the transmission of certain helminths which must undergo a period of maturation before becoming infectious (e.g. Ascaris). Pathways of faceo-oral transmission

8. Epidemic patterns in relation tothe mode of transmission Some of the infections that are acquired through the gastro-intestinal tract characteristically occur in epidemic form, for example typhoid. The pattern of an epidemic is affected by the route of transmission. A water-borne epidemic is typically explosive: it may affect people over a wide area who have no other traceable connection but the use of the same water supply. Food-borne outbreaks may be more localized, affecting persons from the same household or board in institution, those who feed communally at a hotel, restaurant, aeroplane or staff canteen, or those who have taken part in a festive dinner or picnic.

9. HOST FACTORS Non-specific factors in the host pay some part in preventing infection through the gastro-intestinal tract. The high acid content and the antibacterial lysozyme in the stomach, and the digestive juices in the upper part of the intestinal tract destroy potentially infective organisms but do not constitute an immune barrier to infection. More significant is the specific immunity which can be derived from previous infections or from artificial immunization? Immunity is in part related to specific antibodies in the sera of those previously infected or artificially immunized. It has also been demonstrated that the intestinal mucosa may acquire resistance to certain pathogens such as cholera or poliomyelitis:this local resistance is mediated through a fraction of immunoglobins(IgA) which are secreted by the mucosa.

10. CONTROL OF THE INFECTIONSACQUIRED THROUGH THEGASTRO-INTESTINAL TRACT Control can operate on each of the three components of infection: 1. The infective agent: ■ sanitary disposal of faeces; ■ elimination of human and animal reservoirs. 2 .The route of transmission: ■ provision of safe water supply; ■ protection of food from contamination; ■ control of flies; ■ improvement of personal hygiene. 3 .The host: ■ specific immunization; ■ chemoprophylaxis; ■ specific treatment

11. DIARRHOEAL DISEASES Diarrhoeal diseases, as a group, remain a major cause of death in developing countries, especially in preschool children. Children under 3 years of age may experience as many as 10 episodes of diarrhoea per year. The main agents are: ■ Enteroviruses, :rotavirus. ■ Escherichia coli:( bacteria) (a) Enterotoxigenic E. coli (ETEC) (b) Localized-adherent E. coli (LA-EC) (c) Diffuse-adherent E. coli (DA-EC) (d) Enteroinvasive E.coli (EIEC) (e) Enterohaemorrhagic E. coli (EHEC) ■ Campylobacter spp. ■ Shigella ■ Vibrio cholerae01 and 0139 ■ Salmonella (non-typhoid) ■ Entamoeba histolytica(an anaerobic parasitic amoebozoan) ■ Giardia lamblia ■ Cryptosporidium.

12. ACUTE DIARRHOEA Most episodes of diarrhoea last less than 7 days and can be effectively treated with oral rehydration, combined with an appropriate diet. Limited evidence suggests that vitamin A deficiency predisposes to increased risk of diarrhoeal illness and to increased risk of death in preschool children. Children with diarrhoea but no dehydration should receive extra fluids at home. If the child is severely dehydrated – swollen eyes, drinking poorly – take child to nearest hospital.

13. PERSISTENT DIARRHOEA Persistence of an acute diarrhoeal episode for at least 14 days occurs in 3–20% of cases. This leads to significantly increased mortality: 14% of persistent cases are fatal compared with 1% of acute cases. Risk factors in the development of persistent diarrhoea include: ■ age. ■ nutritional status. ■ immunological status. ■ previous infections. ■ concomitant or associated enteropathogenic bacteria (e.g. enteroadherent E. coli; enteropathogenic E. coli and cryptosporidia)

14. CONTROL Programmes for the reduction of morbidity and mortality include: ■ oral rehydration therapy – highly effective in preventing death from dehydration in acute episodes. ■ promotion of breast-feeding (exclusively for 4 months: continue for 2 years). ■ improving weaning practices (soft & small serving of vegetable oil). ■ improving water supply and sanitation (safe water: use of latrines: safe disposal of stools). ■ promoting personal and domestic hygiene (handwashing: prevent contamination of food). ■ immunization (measles). ■ specific chemotherapy for invasive bowel infections or presence of Helicobacter pylori. ■ zinc supplementation. Not all interventions are appropriate everywhere. Each country must decide which package of measures is likely to be most feasible and cost-effective. Rota viruses and cholera immunization must await the results of field trials of the new vaccines.

15. VIRAL INFECTIONS The most common viral infections transmitted through the gastro-intestinal tract are: ■ Rotaviruses. ■ Poliomyelitis. ■ Viral hepatitis A. ROTAVIRUSES Rotaviruses are the most common cause of diarrhoea worldwide, virtually all children have been infected by the age of 4 years. The incubation period is short – 24–48 hours – with vomiting, fever and a watery diarrhoea the presenting clinical features. Epidemiology Most infections are caused by group A viruses, The reservoir of infection is humans and transmission occurs by the faeco-oral route due to poor standards of personal and environmental hygieneVirusshedding continues for about 8 days. The peak age-specific prevalence is in children between 6 and 24 months.

16. Diagnosis Rotaviruses are identified in the stool by ELISA, electron microscopy, or passive particle agglutination techniques?. Control INDIVIDUAL Oral, subcutaneous or intravenous rehydration. COMMUNITY High standards of personal hygiene and sanitary practices should be employed, although these may not be entirely successful because the virus survives in contaminated water, on hands and is resistant to commonly used disinfectants. An effective vaccine was produced but has recently been withdrawn because of unexpected and serious adverse effects. Newer vaccines are being evaluated.

17. POLIOMYELITIS poliomyelitis was the most important enterovirus in the tropics but widespread immunization programmes have greatly reduced the incidence of the disease. the disease will be eradicated within the next 5 years .The incubation period varies from 3 to 21 days, with an average of about 10 days. Poliomyelitis is a notifiable disease. It is characterized by fever and a flaccid asymmetrical paralysis. Epidemiology The disease is now limited to a few countries in the tropics. All of the known types of poliomyelitis (1, 2 and 3) are prevalent although the virus strains responsible for paralytic illness in any area may vary, and at different periods in the same area one type or other may predominate. Large-scale epidemics may result if virulent wild-type virus (commonly type 1) is reintroduced into a community with breakdown in vaccine delivery and poor economic and environmental conditions. In the tropics, a seasonal peak occurs in the hot and rainy season.

18. RESERVOIR Humansare the reservoir of infection. The poliovirus is excreted in the stools of infected cases, convalescent patients and health carriers. TRANSMISSION Poliomyelitis is a highly infectious disease. The virus is transmitted from person to person by the faecal–oral route or pharyngeal secretions, rarely by foodstuffs contaminated by faeces. Virology There are three distinct types of poliovirus, that invade the central nervous system: type 1 ,type 2 and type 3 . The viruses grow well in tissue culture, they resist desiccation but are killed in half an hour by heat (60°C). Most outbreaks are due to type 1 poliovirus.

19. Laboratory diagnosis The virus is isolated from samples of faeces, throat swabs or from throat and nasopharyngeal washings. Clinically, the most important differential diagnosis is Guillain–Barée syndrome, in which the paralysis is usually symmetrical and progresses for longer periods – 10 days instead of 3–4 days as in poliomyelitis. Control High standards of hygiene and mass immunization are the two most important measures of control. IMMUNIZATION Immunization provides the most reliable method for the prevention of poliomyelitis and for controlling rapid spread during an epidemic. Two types of poliomyelitis vaccines are currently available: killed ‘Salk’ vaccine (IPV), which is given by injection, and the attenuated ‘Sabin’ vaccine, which is given by mouth (OPV).

20. ERADICATION In 1988 WHO declared the goal of eliminating poliomyelitis in the world due to wild-type virus by the year 2000. The strategy is four-pronged comprising: (i) high routine immunization coverage with OPV. (ii) supplementary immunization in the form of national immunization days (NIDs). (iii) effective surveillance. (iv) in the final stages, door-to-door immunization campaigns in areas where the virus persists.

21. VIRAL HEPATITIS There are six types of viral hepatitis – A and E, which are transmitted by the faeco-oral route, and B, C, D and G, which are blood-borne infections. Viral hepatitis A (HAV) The disease is characterized by loss of appetite, jaundice, enlargement of the liver and raised levels of liver enzymes. The incubation period varies from 15 to 40 days with an average of around 20 days. EPIDEMIOLOGY The disease is widespread but is more common in the tropics and subtropics; in these areas, most infections are acquired in childhood and many are subclinical. Reservoir Humans are the reservoir of infection, excreting the organism in the faeces and possibly urine, virus shed in the faeces continues until the onset of clinical symptoms.

22. Transmission Faeco-oral spread is the most important mode of transmission by direct or indirect contact. Sporadic cases are probably caused by person to person contact, but explosive epidemics from water and food occur. Food handlers can disseminate the infection. The ingestion of shellfish grown in polluted waters is attended by a risk of acquiring hepatitis A. Host factors ■ Age – children tolerate the infection and recover more rapidly than adults. ■ Sex – men take longer than women to recover from an equivalent degree of liver damage. ■ Pregnancy – exacerbates hepatitis. ■ Strenuous exercise – in the early stages of the disease. ■ Glucose-6-phospate deficiency – a high frequency of G6PD deficiency has been found among patients with hepatitis and those with this genetic enzyme defect have a longer and more severe course.

23. VIROLOGY AND LABORATORY DIAGNOSIS HAV is in the range of 25–28 nm?and is identified by electron microscopy. Elevation of serum levels of liver enzymes? is invariably found. The diagnosis is confirmed by the demonstration of IgM antibodies to the virus measured by solid phase, IgM capture immunoassays. CONTROL Control depends on high standards of personal and environmental hygiene, for example proper sewage disposal, safe drinking water. Immunizatio Inactivated HAV vaccine is now available. A double-dose vaccine has been licensed which, if followed by a booster dose 6–12 months later, is expected to provide at least 10 years’ protection. It induces antibodies in over 90% of individuals within 2 weeks and protects against infection. The vaccine should be given intramuscularly in the deltoid region. Unfortunately, HAV vaccines are at present too expensive for use on a population-wide basis in most tropical countries. Passive immunity may be conferred using human immunoglobulin (IG). Even when it does not prevent infection it does modify the severity of the disease. It is useful in protecting family contacts during epidemics (0.2 ml/kg intramuscularly). For those going to the tropics a 0.2–0.5 ml/kg gives passive protection for about 6 months. Recovery from a clinical attack creates a lasting active immunity.

24. Viral hepatitis E (HEV) Like HAV, HEV causes malaise, anorexia, jaundice and liver enzyme serum elevation. The incubation period is around 40 days, a case fatality rate of 20% occurred in pregnant women in India, while 60% of sporadic cases of fulminant hepatitis seen in the country are all due to HEV . EPIDEMIOLOGY Subsequent to the Indian epidemic, hepatitis E has been reported from a number of countries in the tropics ranging from China to Mexico. The source of infection has been contaminated drinking water. The peak age specific sero-prevalence in endemic countries is in the over-16 years group – unlike hepatitis A, which usually occurs before the age of 5 years. Clinical manifestations occur in persons 25–40 years of age. Autochthonous cases of hepatitis E are rare in Western Europe and the USA. CONTROL As for HAV, provision of safe drinking water and sanitary disposal of faeces is required to prevent the infection. No vaccine is as yet available.

25. Hepatitis B (HBV) Hepatitis B is not transmitted by the faeco-oral route but is a blood-borne agent, transmitted by inoculation. Hepatitis B virus causes long-incubation hepatitis. It also gives rise to one of the 10 most common cancers, heptocellular carcinoma. There is evidence that HBV is the aetiological agent in up to 80% of cases. EPIDEMIOLOGY The carrier state (defined as the presence of HbsAg for more than 6 months) rises from 0.1% in parts of Europe to 15% in several tropical countries, a large number of infections are acquired in the perinatal period, usually from a carrier mother. Transmission may occur by: ■ transfusion of blood or blood products. ■ accidental inoculation, e.g. repeated use of hypodermic needles without adequate sterilization. ■ insect bites. ■ perinatally – from a carrier mother. ■ sexual intercourse – hetero- and homosexual. ■ serous exudates of skin ulcers. ■ injury-associated sports or jobs.

26. VIROLOGY HBV possesses at least three separate antigens: surface antigen (HbsAg); core antigen (HbcAg) and enzyme antigen (HbeAg). The HbcAg is a valuable marker of potential infectivity of HbsAg positive serum. Subdeterminants of both surface antigen and c antigen occur. CONTROL Control is carried out by a combination of: (i) counselling; (ii) hygiene practices in high-risk areas; (iii)vaccination of at- risk individuals; and (iv) selective use of hepatitis B immunoglobin (HbIG). A recombinant HbsAgvaccine is now widely used. Three doses (at 0, 1 and 6 months) are required for complete protection. Vaccination is required for groups at high risk of infection (e.g. health-care staff in contact with blood or patients, homosexuals, drug users, etc.) WHO has recommended that all children should be vaccinated during the first year of life. In countries where perinatal transmission is frequent, vaccination should be done at or soon after birth.

27. Hepatitis C (HCV) Hepatitis C virus was discovered in 1989, and contains six different genotypes (1–6) which vary in their geographical destination. The incubation period from exposure to liver function abnormalities is usually 8 weeks. Chronic infection is generally asymptomatic at first, later a large proportion of cases progress to cirrhosis of the liver and some to hepatocellular carcinoma. EPIDEMIOLOGY HCV has a worldwide distribution. The route of infection is parenteral (e.g. intravenous drug users, blood transfusion). Donor HCV sero-prevalence is high in Egypt. Transplanted organs may also transmit the infection. Unsterile needles in medical and dental procedures, tattooing and other perisubcutaneous procedures are also responsible.

28. CONTROL ■ For the individual, interferon is now generally prescribed for the treatment of chronic hepatitis. ■ Screening of blood donors has proved effective in reducing transmission of HCV. ■ Education, greater availability of disposable needles. ■ No vaccine is currently available. Hepatitis delta (HDV) HDV is a small, incomplete virus incapable of independent replication, which can exist only in the presence of HBV. It gives rise to a more severe form of hepatitis. Two forms of infection have been recognized. Like HBV, HDV is a blood-borne pathogen. Delta hepatitis is endemic in the Eastern Mediterranean, the Middle East, North Africa, the Amazon but occurs worldwide. CONTROL ■ HBV vaccination also protects against HDV. ■ Screening of blood has reduced the risk of infection.

29. Hepatitis G (HGV) HGV has a similar role to HCV and should be sought in haemophilia, thalassaemia, dialysis patients, intravenous drug addicts and those handling blood. Co-infection with HCV is frequent. REFERENCES Rowitz, Louis. 2008. Public Health Leadership: Putting Principles into Practice.