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Salmonella Part 2: Typhoidal Salmonella

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The typhoidal Salmonella serotypes are Typhi and Paratyphi, which are responsible for causing typhoid and paratyphoid fever (collectively referred to as enteric fever). Unlike non-typhoidal salmonella, these serotypes are only found in humans and are typically acquired through the consumption of food or water contaminated with human feces. A small percentage of infected individuals may become chronic asymptomatic carriers. Typhoidal salmonella infections are commonly seen in developing countries with poor sanitation, particularly in areas of South, Central, and East Asia, as well as Southern Africa.

In order to cause systemic illness, typhoidal Salmonella crosses the intestinal barrier by penetrating enterocytes and M cells, then gets taken up by host macrophages and phagocytes, spreading throughout the body. It possesses a special polysaccharide antigen called the Vi (virulence) capsular antigen that resists the host's immune defenses. Enteric fever is characterized by a stepwise fever, relative bradycardia, a "rose spots" rash, and abdominal pain. Severe complications can develop if left untreated, including hepatosplenomegaly, intestinal bleeding, perforation, peritonitis, and sepsis. Treatment usually involves antibiotics like fluoroquinolones or azithromycin, and in some cases, prevention can be achieved with a vaccine.

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What are the main differences between typhoid fever and paratyphoid fever?

Both typhoid fever and paratyphoid fever are types of enteric fever caused by typhoidal Salmonella serotypes. Typhoid fever is caused by Salmonella enterica serovar Typhi, while paratyphoid fever is caused by Salmonella enterica serovars Paratyphi A, B, or C. Although the symptoms and severity of the two diseases are similar, paratyphoid fever is often milder and has a shorter duration than typhoid fever. Furthermore, the available vaccines against typhoid fever do not provide protection against paratyphoid fever.

How is typhoidal Salmonella transmitted, and what are the main prevention methods?

Typhoidal Salmonella is transmitted primarily via the fecal-oral route, either through direct contact with an infected person's fecal matter or by ingesting contaminated food or water. The main prevention methods include proper sanitation and hygiene practices, such as washing hands thoroughly, drinking clean water, and avoiding consumption of potentially contaminated food. In addition, vaccination against typhoid fever may provide some protection for those living in or traveling to high-risk areas.

What are the clinical manifestations of a Salmonella infection caused by typhoidal serotypes?

Salmonella infections caused by typhoidal serotypes typically result in enteric fever, which includes typhoid fever and paratyphoid fever. Symptoms may include high fever, headache, fatigue, abdominal pain, constipation or diarrhea, and a rash. In severe cases, intestinal bleeding or perforation, altered mental status, and even death may occur. These symptoms usually begin within 7-14 days after exposure to the bacteria and can last for several weeks if left untreated.

What is the role of antibiotics in treating typhoidal Salmonella infections, and what are some challenges in their use?

Antibiotics are crucial in the treatment of typhoidal Salmonella infections to reduce the severity and duration of the illness, prevent complications, and decrease mortality. Commonly used antibiotics include fluoroquinolones, third-generation cephalosporins, and azithromycin. However, the emergence of antibiotic-resistant strains of Salmonella poses a significant challenge to treatment. This necessitates proper antibiotic stewardship and constant monitoring of resistance patterns to guide appropriate antibiotic therapy.

How effective is the typhoid vaccine, and who should receive it?

The typhoid vaccine provides moderate protection against typhoid fever, with efficacy ranging from 50-80%, depending on the vaccine type (injectable Vi polysaccharide vaccine or oral live-attenuated vaccine). The vaccine is not effective against paratyphoid fever or non-typhoidal Salmonella infections. It is recommended for people living in or traveling to high-risk areas, individuals with certain medical conditions, and close contacts of chronic carriers. The vaccine should not replace proper hygiene practices and should be used in conjunction with other preventive measures, such as access to clean water and safe food handling.