Introduction
Salmonella typhi is a rod-shaped, motile, gram-negative bacterium which causes typhoid fever in human beings. This pathogen is an issue of public health concern worldwide. It affects about 26 million people globally every year and contributes to economic burdens in terms of the cost of prevention, surveillance, and treatment (Tanmoy et al., 2018). The disease is most prevalent in underdeveloped countries and industrialized regions such as Africa, India, South America, and Southeast Asia.
Salmonella typhi is transmitted through water, food and contact with an infected person. Animals used as food such as poultry, cattle, and swine are the main Salmonella infection sources. This pathogen is disseminated through traded food and the transportation of uncooked animal products. Mortality rate of patients infected with this bacterium has been increasing due to the development of more infectious antimicrobial resistant strains.
Pathology and Symptomatology
Salmonella infections severity depends on the involved serotype, strain, and the health status of an individual. Children under 5 years old, people with immunosuppression, and elderly people are more susceptible to the pathogen relative to young adults (Gibani et al., 2019). In the host, pathogenicity is achieved after the bacteria invade the host and replicates to enhance survival in the human cells. Bacteria penetrate the intestinal wall epithelium after entering the digestive tract through contaminated food or water. To gain access into human cells the organism induces phagocytosis.
The engulfed Salmonella typhi is then encased in a host vacuole, immune response against the foreign bacteria will not be activated in the human body because the pathogen injects effector proteins into the vacuole by using a type III secretion system. The proteins cause changes in vacuole compartment structure, which allows the new microbe to survive and replicate. Thereafter, the pathogen moves to the reticuloendothelial system where they settle and multiply.
Salmonella typhi causes typhoid fever also referred to as enteric fever, after infection, the pathogen enters at least one-week incubation period, which is characterized by symptoms such as abdominal pain, constipation, headache, and diarrhea. Elderly patients with immunosuppression are likely to experience constipation while diarrhea occurs in children. The illness phase then follows, at this stage fever patterns alternate from low-grade, which is below 37.5°C to high-grade ranging from 38.2°C to 41.5°C (Karkey et al., 2018). Other symptoms associated with this disease include bradycardia, myalgia, hepatomegaly, rose spots on the abdomen and chest, and splenomegaly. In endemic areas, infected patients develop complications such as hepatitis, pancreatitis, and cholecystitis.
Human beings and animals are the reservoir of S. typhi, they shed the bacteria through their stools, which contaminates water and food. In endemic regions, some patients become chronic typhoid carriers, and they pass salmonella in their feces for several years post-acute infection phase. High mortality rate and morbidity are associated with the disease in underdeveloped regions such as Africa, Central and South America, and the Middle East.
Prevention and Treatment
The main S. typhi transmission is through the oral-fecal path, it is generally spread by eating or drinking contaminated water and food. Since the incidence of typhoid fever is high in South America, India, Southeast Asia, and Africa (Karkey et al., 2018), people should be cautious about what they ingest when visiting these regions. Thus, to avoid being infected, one should not drink well or tap water unless it is boiled, it is only safe to drink hot tea, pasteurized milk, hot coffee, bottled water, and carbonated drinks.
In terms of food, one should avoid raw meat, fruits, vegetables, and fish when in endemic areas, also eating should be restricted to inspected hotels rather than street vendors. Good hygiene is critical in controlling typhoid spread, thus, washing of hands before eating and after visiting washrooms is highly recommended. Avoiding contact with sick people and washing hands after visiting them and before preparing meals helps in curbing the disease spread.
A blood test or stool cultures are used to confirm S. typhi presence in the body, one is treated with antibiotics such as fluoroquinolones, ceftriaxone, and azithromycin if the test turns positive. Vaccinations are also effective in preventing infection; there are two types of typhoid vaccine, the inactivated one for children and the live typhoid vaccine for individuals above 6 years (Gibani et al., 2019). However, it is only given to people with risk factors such as those traveling to endemic areas, those in contact with a sick person, laboratory staff working with S. typhi, and carriers.
Why I Choose to Study Salmonella Typhi
Salmonella typhi is a bacterium of great concern in public health globally. It is estimated that between 11 and 21 million people in the world are diagnosed with typhoid infections annually and about 5,700 people are hospitalized yearly in the United States (Gibani et al., 2019). Antibiotic drugs such as ampicillin, arechloramphenicol, cephalosporins trimethoprim-sulphamethoxazole, which have been the main treatment drugs against typhoid fever. However, these medications are not very effective anymore due to emergent of drug resistance bacterium strain.
The progressive emergence of resistant Salmonella typhi strains against antimicrobial drugs makes the pathogen an interesting organism for study. The mechanism of resistance in the pathogen includes change of target sites, active efflux, and inactivation of drugs. Initially, pills such as trimethoprim-sulfamethoxazole, ampicillin, and chloramphenicol were first-line treatment effective against typhoid. However, by the 1990s amoxicillin, chloramphenicol, and co-trimoxazole had already been rendered inactive.
Antibacterials with fluoroquinolones as the active agent such as ciproflaxin is currently used in most part of the world. However, there is an emergent strain resistant to the drug in South Asia, which is threatening to spread globally. For this reason, third-generation medicines such as azithromycin and cephalosporins were adopted widely to prevent typhoid outbreak. However, resistance to cephalosporins has been reported in Pakistan (Alikhan et al., 2018). Thus, there is a need for the development of alternative drugs for the treatment of S. typhi infections to avoid massive loss of lives in the future. In addition, rational use of antibiotics in society is necessary to reduce multidrug resistance.
Conclusion
Typhoid fever is a current global health problem due to the diminishing treatment option attributed to antimicrobial resistance. Since it accounts for a massive disease burden each year, alternative drugs such as tigecycline and carbapenems which were not used as first-line treatment need to be utilized to curb the disease. Additionally, research resources should focus on the development of new drugs effective against specific serotypes. This will be achievable only through researching and documenting emergent strains and their susceptibility to medication.
Availability of clean drinking water, improvement of sanitation especially in public facilities, adoption of hygiene measures when handling food, and creating public health awareness and education are efficient in controlling the infection. Only individuals with risk factors are eligible for the typhoid vaccine at the present. It will be prudent to undertake mass immunization in endemic regions using injectable unconjugated Vi typhoid vaccine or live attenuated Typhi 21a to reduce disease burden.
References
Alikhan, N. F., Zhou, Z., Sergeant, M. J., & Achtman, M. (2018). A genomic overview of the population structure of Salmonella. PLoS Genetics, 14(4), e1007261.
Gibani, M. M., Voysey, M., Jin, C., Jones, C., Thomaides-Brears, H., Jones, E., & Pollard, A. J. (2019). The impact of vaccination and prior exposure on stool shedding of Salmonella Typhi and Salmonella Paratyphi in 6 controlled human infection studies. Clinical Infectious Diseases, 68(8), 1265-1273.
Karkey, A., Thwaites, G. E., & Baker, S. (2018). The evolution of antimicrobial resistance in Salmonella Typhi. Current Opinion in Gastroenterology, 34(1), 25-30.
Tanmoy, A. M., Westeel, E., De Bruyne, K., Goris, J., Rajoharison, A., Sajib, M. S., & Endtz, H. P. (2018). Salmonella enterica serovar Typhi in Bangladesh: exploration of genomic diversity and antimicrobial resistance. MBio, 9(6).