Identification and Genotyping of Patients Living With Typhoid Fever Using Molecular Markers

Identification and Genotyping of Patients Living With Typhoid Fever Using Molecular Markers

Typhoid or enteric fever is an ancient disease, which has afflicted mankind since human populations grew large enough to contaminate their water and food supplies. It is caused by Salmonella enterica serovar typhi (previously known as salmonella typhi), a pathogen specific only to humans, as well as by certain non-typhoid salmonella (NTS), particularly Paratyphoid strains A, B, C. These waterborne gram negative aerobes are associated with poor sanitation and fecal contamination of water and food supplies. The syndrome needs to be distinguished from that caused by many other organisms. Today there are as many as 16-30 million cases per year, almost exclusively in the developing world, with a mortality rate of 10%. Recent developments in the mapping of the Salmonella genome have provided in sights into its pathogenicity and how antibiotic resistance and human immunity develop. Typhoid fever is important surgically because abdominal complications such as intestinal perforation, bleeding, cholecystitis and pancreatitis represent the most serious complications of the illness. Typhoid perforation of the ileum is one of the most common causes of bowel perforation in the developing world. Typhoid fever is caused by Salmonella typhi , a Gram-negative bacterium. A very similar but often less severe disease is caused by Salmonella serotype Paratyphi A. The nomenclature for these bacteria is confused because the criteria for designating bacteria as individual species are not clear. Two main views on the nomenclature of the genus Salmonella have been discussed. S. enteric included six subspecies, of which subspecies I (one) contained all the pathogens of warm-blooded animals. S. typhi was a serotype within subspecies I: Salmonella enteric subspecies I serotype typhi. Typhoid fever, also known as enteric fever, is a potentially fatal multisystemic illness caused primarily by Salmonella enterica, subspecies enterica serovar typhi and, to a lesser extent, related serovars paratyphi A, B,and C.The protean manifestations of typhoid fever make this disease a true diagnostic challenge. The classic presentation includes fever, malaria, diffuse abdominal pain, and constipation. Untreated, typhoid fever is an illness that may progress to delirium, obtundation, intestinal hemorrhage, bowel perforation, and death within 1 month of onset. Survivors may be left with long-term or permanent neuropsychiatric complications. S typhi has been a major human pathogen for thousands of years, thriving in conditions of poor sanitation, crowding, and social chaos. The name S typhi is derived from the ancient Greek ‘ typhos’ an ethereal smoke or cloud that was believed to cause disease and madness. In the advanced stages of typhoid fever, the patient’s level of consciousness is truly clouded. Although antibiotics have markedly reduced the frequency of typhoid fever in the developed world, it remains endemic in developing countries (Mc Conkey, 2009).

Typhoid fever was not well understood in the ancient world, probably because its symptoms are not primarily diarrhea, but rather systemic and non-specific. Typhoid fever was frequently associated with military campaigns and was a significant cause of death in the American Civil War and Boer War where death from typhoid exceeded those from combat. With recognition that fecal contamination of food and water supplies was the main mode of transmission of the illness and measures taken to prevent these typhoid fever has been restricted, in industrialized countries, to localized epidemics and infections in travelers returning from endemic areas.
OBJECTIVES: To control of the dissemination of the causative agent.

AIM: To determine the genotype of typhoid fever affected patients using mol


The genus Salmonella of family Enterobacteriaceae containing more than 2540 serotypes is now considered to comprise of two species: Salmonella enterica and Salmonella bongori. There are six subspecies of Salmonella enterica: S. enterica subsp. enterica, S. enterica subsp. salamae, S. enterica subsp. arizonae, S. enterica subsp. diarizonae, S. enterica subsp. houtenae, and S. enterica subsp. indica. The most important Salmonella subspecies is S. enterica subsp. enterica, which contains more than 1500 serotypes including the typhoid and paratyphoid bacilli. Salmonellae are Gram negative, motile, facultative anaerobe, non-spore forming flagellated bacilli which are 2-3 μm long and 0.4-0.6 μm in diameter. Salmonella infections in humans include mainly typhoid fever, caused by S. enterica subsp. Enterica serovar Typhi (S. Typhi) and paratyphoid fever which is caused by S. enterica subsp.enterica serovar Paratyphi A (S. Paratyphi A). These infections are commonly called as enteric fever which continues to be one of the most serious public health problemsworldwide S. Paratyphi B and C have also been reported to cause human infections. (Parry et al, 2012)

Salmonella infection is a major cause of bacterial enteric illness in both humans and animals. It ranges clinically from the common simple gastroenteritis (diarrhea, abdominal cramps and fever) to the complicated enteric fevers (including typhoid fever), which are fatal and cause bacteremia and inflammatory destruction of intestine and other organs requiring an appropriate antibiotic therapy. Salmonella bacilli are frequently found in sewage, river and other waters and soil. Typhoid fever, besides affecting school age children and young adults, is also an important cause of morbidity among infants and toddlers in whom high rates of complications and hospitalization have been documented. The Salmonella that cause typhoid fever spread mainly from person-to-person via fecal-oral route and have no significant animal reservoir. The World Health Organization (WHO) estimates that the annual approximate global burden of typhoid is 22 million new cases and 200,000 deaths. More than 90% of these enteric fever episodes are thought to occur in Asia. In contrast to that seen in the rich countries, typhoid fever remains an important cause of illness in the developing world where annual incidences in Papua New Guinea and Indonesia may reach 1200/100,000 population. A recent epidemiologic study showed that south-east and south-central Asia are the regions of highest endemicity with rates greater than 100/100,000 cases per year; the rest of Asia, Africa, Latin America, the Caribbean and Oceania (except Australia and New Zealand) are the next highest with incidence rates of 10-100/100,000 and Europe, North America and the rest of the developed world have low rates of disease. Typhoid fever represents the 4th most common cause of death in Pakistan. .The majority of patients, 60-90%, are treated as outpatients and, therefore, hospital based studies will underestimate true incidence. Two hospital based case-control studies from Vietnam found that risk of infection was related to recent contact with an infected person, lack of education and drinking untreated water. S. paratyphi A, which normally causes about 15-20% of cases of typhoid fever in Asia, increasingly is becoming a pathogen in India and China, possibly due to vaccination against S. typhi. Recent epidemiologic studies also show the rise of multi-drug resistant (MDR) organisms. In a study of 1100 hospitalized children in Pakistan, the mortality rate of 1.6% was found to be related to younger age and MDR infection. Traditionally the age range considered to be at greatest risk was 5-25 years. However this has been questioned in a study from a private laboratory in Bangladesh, which found that the 57% of S. typhi isolates were in children less than 5 years of age and 27% less than 2 years. This has significant implications for vaccination policies. In 2001 the entire genome of a MDR isolate of S. typhi was sequenced. This showed that Salmonella share more than 70-80% of genes with other enteric bacteria, like E. coli. Another feature of S. typhi genome is the presence of over 200 inactivated genes which are felt to be related to the adaptation of the bacteria to the human host and possibly its ability to invade human tissue. Drug resistance is encoded in a transmissible plasmid. The development of additional horizontal genes in the salmonella pathogenicity islands (SPI) represented the separation of the E. Coli and Salmonella lineages and allows for the targeting of intestinal epithelial cells by Salmonella. (Casner, 2011)

Typhoid fever differs from other gastroenteritis as it is mainly an infection of blood stream, although the onset of the disease requires the oral ingestion of the causative bacteria via contaminated food and water. Salmonella must survive the gastric acid barrier to reach the small intestine and to be fully pathogenic the Salmonellae must have different characters called virulence factors. These include a complete lipopolysaccharide coat, ability to invade cells, ability to replicate within the cells and possibly the elaboration of toxins. In the small intestine, the bacteria adhere to mucosal cells and then invade the mucosa of the distal small intestine by Type III secretion system; destroying specialized epithelial M cells. After penetration, the bacteria translocate to the intestinal lymphoid follicles and the draining mesenteric lymph nodes while a few pass on to the reticulo-endothelial cells of the liver and spleen. Then bacteria are released into the bloodstream and many of the bacilli are lysed by the combined action of antibodies and complement system. The endotoxins liberated from these lysed bacteria cause the patient to develop a high fever. Typhoid bacilli are not annihilated when engulfed by macrophages; instead, they survive and protected from the attack of antibodies. Only cell-mediated immunity may eventually be able to kill these bacilli. This can happen if some of the normal macrophages are converted, through the action of lymphokines, to activated macrophages, which have an increased microcidal activity. (Katz et al, 2010).


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