Paratyphoid Fever

Paratyphoid fever is caused by three serotypes of Salmonella enterica subspecies enterica: Paratyphi A (most prevalent globally, especially South and Southeast Asia, parts of China), Paratyphi B (more common in Africa and historically in Europe), and Paratyphi C (rare, mostly Far East). Like typhoid, transmission is fecal-oral via contaminated water and food, with humans as the only reservoir for Paratyphi A and C, while Paratyphi B has occasional animal reservoirs. The infectious dose, pathogenesis, and tissue tropism (Peyer's patches, mesenteric lymph nodes, spleen, liver) are similar to S. Typhi.

Clinical features parallel typhoid but are generally milder, with shorter duration of fever (10-15 days vs 3-4 weeks for typhoid), less prominent rose spots, lower frequency of severe complications, and lower mortality. However, severe disease and complications—including intestinal perforation, hemorrhage, hepatitis, encephalopathy, and chronic carriage—do occur, particularly with Paratyphi A. Incubation is typically 6-30 days. Symptoms include rising fever, headache, malaise, abdominal pain, gastrointestinal symptoms (constipation more common than diarrhea, but variable), hepatosplenomegaly, and rose spots in some cases.

Diagnosis requires culture-based methods—blood culture (60-80% in first week), bone marrow culture (>90% sensitivity), and stool culture in later weeks. Widal test cannot reliably distinguish between typhoid and paratyphoid due to cross-reactivity, and lacks utility in endemic regions. Treatment: third-generation cephalosporins (ceftriaxone), azithromycin, or fluoroquinolones (when susceptible) for 10-14 days. Concerns about increasing fluoroquinolone resistance in Paratyphi A in South Asia have led to increased use of azithromycin and ceftriaxone. Importantly, current typhoid vaccines (Ty21a, Vi polysaccharide, Vi-conjugate) do not provide cross-protection against Paratyphi infections, leaving travelers and endemic populations vulnerable; promising bivalent and trivalent vaccines targeting both typhoid and paratyphoid are in development.