BIOLOGY Volume 2 - A Guide to General Biology - 2004

15. HEALTH AND DISEASE

15.3. Infectious Diseases

15.3.5. Typhoid and Paratyphoid Fevers (Salmonella typhi and S. paratyphi)

Until recently, typhoid fever was one of the scourges of humanity. This infection goes hand in hand with poverty and overcrowding, and outbreaks typically occurred during times of war and devastation. Typhoid was widespread in the UK until 1875, when the Public Health Act passed that year turned the tide. Improvements in sanitation—most importantly, the more rigorous purification of drinking Water—dramatically reduced the risk of epidemics.

In recent years, around 200 cases of typhoid fever have been recorded in England and Wales, though the majority of those infected contracted the disease while on holiday abroad. Unfortunately, no country has yet managed to completely eradicate the causative agents of the disease. Asymptomatic carriers serve as a constant reservoir for these Bacteria.

Typhoid and paratyphoid fever (a salmonella infection with typhoid-like symptoms) are caused by members of the genus Salmonella—Salmonella typhi and S. paratyphi, respectively. The symptoms of these diseases are similar, but paratyphoid is usually milder.

Modes of Transmission and Symptoms

Pathogenic bacteria are present in the feces of infected individuals or asymptomatic carriers. The infection is typically transmitted via contaminated water or food. Because a very small number of microorganisms is enough to cause typhoid fever, the disease is classified as highly infectious. Unlike typhoid fever, paratyphoid and other salmonella infections (see below) have a low infectivity, meaning that a much larger number of pathogens is required for symptoms to manifest. The most Common sources of infection are outlined below.

1. Drinking water. Drinking water becomes contaminated with feces As a result of direct sewage discharge into water bodies, leaking cesspools, or damaged pipes. Salmonella can survive in liquid feces for about a week, and even longer when diluted with clean water.

2. Dairy and meat products. Salmonella can enter milk via the unwashed hands of an asymptomatic carrier or through equipment washed with untreated water. Contaminated milk has caused several typhoid outbreaks in England, such as those in Epping in 1931 (260 cases, 8 fatalities) and Bournemouth in 1938 (718 cases, 70 fatalities). An outbreak of the disease in Aberdeen in 1964 was linked to contaminated beef.

3. Seafood. Edible bivalve Mollusks, such as oysters and mussels, feed by filter-feeding. As a result, they accumulate pathogens present in the water within their Tissues.

Once ingested by a human, Salmonella bacteria migrate to the Lymph Nodes, where they multiply during an incubation period lasting approximately 10 days. The bacteria then enter the bloodstream, causing the patient to experience fever, headache, and Muscle aches. A faint rash that fades upon pressure sometimes appears. During the second week of the disease, diarrhea and confusion set in. The third week is considered critical—the patient's condition is very severe, complications develop (Bronchitis, Pneumonia, meningitis), and a fatal outcome is possible.

Because typhoid fever is relatively rare in the UK, it is usually not diagnosed immediately. A recent travel history to a developing country, followed by a fever accompanied by the other symptoms listed above, should raise suspicion of the disease. The Diagnosis is confirmed by a Blood test demonstrating the presence of S. typhi (via culture) or Antibodies against the pathogen.

Treatment and Prevention

Before the advent of Antibiotics, the mortality rate from typhoid fever reached as high as 20%. The Introduction of chloramphenicol and ampicillin helped reduce this figure to 1–5%.

Patients should be isolated, and their feces handled with extreme care. Key preventive measures include adequate sewage and drinking water treatment, personal hygiene, and sanitary conditions in food Processing and retail facilities. A mandatory element of typhoid prevention is controlling flies, which act as mechanical vectors for fecal material (see also Section 15.3.1).

An effective vaccination method exists using a suspension of bacterial capsule Polysaccharides. The vaccine is administered subcutaneously and often causes a strong reaction—the injection site becomes painful and swollen, and a fever sometimes develops. Vaccination is essential before traveling to regions with a high risk of infection.