what hypothesis were made about typhoid a biological problem
Answers
Answer:
Typhoid fever is a life-threatening illness caused by Salmonella Typhi bacteria. Paratyphoid fever is a life-threatening illness caused by Salmonella Paratyphi bacteria.
Explanation:
The genus Salmonella contains a group of closely related organisms that are pathogenic for humans and other vertebrates. The human disease manifestations caused most frequently by Salmonella serotypes worldwide are typhoid fever and gastroenteritis (reviewed in reference 102). Both illnesses clearly differ with regard to their etiology. Typhoid fever is caused by Salmonella enterica serotype Typhi, a strictly human-adapted pathogen. In contrast, gastroenteritis is caused by zoonotic nontyphoidal Salmonella serotypes, with Salmonella enterica serotypes Typhimurium and Enteritidis being isolated most frequently (67).
A second difference between typhoid fever and gastroenteritis is the host response elicited at the site where both infections originate, the intestinal mucosa. Gastroenteritis is a typical diarrheal disease characterized by a massive neutrophil influx in the terminal ileum and colon and the predominance of neutrophils in stool samples of patients (16, 41, 66). In contrast, typhoid fever is not a typical diarrheal disease and the intestinal pathology is characterized by a predominantly mononuclear infiltrate (i.e., macrophages and dendritic cells) (41, 57, 77, 83, 110). Although a fraction (approximately one-third) of typhoid fever patients develop diarrhea, the fecal leukocyte populations in these patients are dominated by mononuclear cells, while neutrophils are scarce (41).
Serotype Typhi and nontyphoidal Salmonella serotypes further differ in their abilities to survive and persist in human tissue. Gastroenteritis is an infection that usually remains localized to the intestine and mesenteric lymph nodes. The incubation period is short (12 to 72 h) and is followed by a short episode of disease (<10 days), suggesting that the infection is efficiently cleared with the onset of adaptive immune responses. In contrast, typhoid fever is a systemic infection during which serotype Typhi colonizes the liver, spleen, and bone marrow in addition to the intestine (i.e., Peyer's patches where perforation may occur) and the mesenteric lymph nodes. Furthermore, typhoid fever is characterized by a considerably longer incubation period (median of 5 to 9 days) and longer duration of symptoms (fever persists for approximately 3 weeks) than that observed in patients infected with nontyphoidal Salmonella serotypes.
The differences in the host responses and disease manifestations of typhoid fever and gastroenteritis suggest that serotype Typhi and nontyphoidal Salmonella serotypes cause disease by different mechanisms. Recent advances in our understanding of the mechanisms by which nontyphoidal Salmonella serotypes cause gastroenteritis have helped in defining the unique properties that enable serotype Typhi to trigger host responses in humans that lead to the development of typhoid fever rather than gastroenteritis.