TYPHOID FEVER

Typhoid fever is an enteric form of (fever) caused by Salmonella typhi, the typhoid bacillus. It is characterized by prolonged fever and multi-system involvement, including lymph nodes, liver, and spleen. The sudden onset of sustained fever, severe headache, and nausea, loss of appetite, constipation or sometimes diarrhea can be life threatening. Severe forms have been described with mental dullness and meningitis. The paratyphoid fever can be caused by any of three serotypes of Salmonella paratyphi A, B and C. It is similar in its symptoms to typhoid fever, but tends to be milder, with a lower fatality rate. In endemic areas, the incidence of typhoid fever is highest in children and young adults from 5-19 years old.

Transmission:

Upon ingestion, typhoid bacilli rapidly penetrate the small intestinal mucosa by transcytosis through M cells and enterocytes, and are taken up by macrophages or diffuse into mesenteric lymph nodes. A primary bacteraemia follows and the pathogen rapidly attains intracellular haven throughout the reticuloendothelial system. This is followed by a sustained secondary bacteraemia associated with clinical illness. S. typhi also shows remarkable predilection for the gall-bladder, where infection tends to become chronic especially in individuals with a pathologic gall-bladder condition.

The disease is almost exclusively transmitted by food and water contaminated by the faeces and urine of infected people and those that are carriers. Polluted water is the most common source of typhoid transmission. In addition, shellfish taken from sewage-contaminated beds, vegetables fertilized with night-soil and eaten raw, contaminated milk and milk products also have been shown to be a source of infection. People can transmit the disease as long as the bacteria remain in their body; most people are infectious prior to and during the first week of convalescence, but 10% of untreated patients will discharge bacteria for up to 3 months. In addition, 2–5% of untreated patients will become permanent, lifelong carriers of the bacteria in their gall-bladder. Usually 10% of the cases can be reduced to less than 1% with appropriate antibiotic therapy. However, strains resistant to chloramphenicol and other recommended antibiotics (ampicillin, cotrimoxazole and even ciprofloxacin) have become prevalent in recent years.

Vaccine:

The two most commonly used are: - oral typhoid vaccine and a single-dose injectable vaccine. These two produces fewer side effects than the older two-dose injectable vaccines. Both vaccines are equally effective and offer 65% to 75% protection against the disease. It is also important to note that, at present no vaccine offers 100% immunity.

The oral vaccine (Vivotif) contains a live but weakened strain of the Salmonella bacteria that causes typhoid fever. The vaccine consists of four capsules that are taken every other day over a one-week period. The capsule protects the vaccine against stomach acid so it remains active when it reaches the intestine where the immunity develops. The oral vaccine can be given either as a first-time dose or as a booster dose. The protection should last about 5 years, at which time another booster dose may be needed. The oral vaccine is not recommended for children under 6 years old.

The single-dose injectable vaccine, (Typhim VI) contains capsular polysaccharide antigen given as a single 0.5 cc/ml intramuscular injection. Immunity is conferred seven days after vaccination and should last for 2 years. Subsequent booster doses are recommended at 2-year intervals. Adverse reactions, which are uncommon, may include discomfort at the injection site, fever and headache. Side effects, while greater than those of the oral vaccine, are much less than those experienced with the old 2-dose injectable vaccine.

The safety of typhoid vaccine during pregnancy is unknown. If typhoid immunization is necessary during pregnancy, the injectable polysaccharide vaccine (Typhim Vi) is probably preferable, because it does not contain live bacteria. Oral typhoid vaccine is safe in HIV-infected individuals as long as their CD4 lymphocyte counts remain above 200.

Breastfeeding is probably protective against typhoid fever in infants.

Due to limited efficacy of the typhoid vaccine, and the fact that many other infections can be acquired from contaminated food and beverages, immunization against typhoid should not in any way limit the importance of following food and water precautions.