Academic journal article Bulletin of the World Health Organization

Vaccination against Typhoid Fever: Present Status

Academic journal article Bulletin of the World Health Organization

Vaccination against Typhoid Fever: Present Status

Article excerpt

Historical overview

Typhoid fever (TF) remains an important public health problem in many developing countries. It has been estimated that about 16 millions cases occur annually in the world, with more than 600 000 deaths. Human beings are the only reservoir and host for this enteric fever which is caused by Salmonella typhi, formerly called Bacillus typhosus, Eberthella typhosa and Salmonella typhosa. Paratyphoid fever is different from TF and is due to S. paratyphi A or S. paratyphi B.

In 1829 C. A. Louis[25] in Paris described typhoid, clearly separating it from other fevers, and related the clinical features to lesions in the intestines, mesenteric lymph nodes and spleen. Bretonneau in France and Smith in the USA recognized the spread of the disease by contagion and the immunity conferred by illness. In 1873 Budd[2] in England provided evidence that bowel discharges were the main, waterborne, mechanism of infection, and in 1880 Eberth[5] discovered the etiologic agent in tissues from a patient infected with TF.

In 1884 Gaffky[10] first cultivated and isolated S. typhi in pure culture from the spleens of infected patients. In 1896, Pfeiffer & Kolle[33] in Germany and Wright[49] in England prepared the first vaccine for human use with heat-killed organisms, and demonstrated that antibodies could passively protect guinea pigs against experimental infection. That same year Widal[46] reported that convalescent-phase serum mixed with S. typhi led to the sticking together of organisms in clumps and losing their motility. Thus was born the term "agglutinins" and the classic serological test for diagnosis of infection by S. typhi.

Epidemiology and clinical aspects

Epidemiology

Typhoid fever continues to be a global health problem. It is difficult to estimate its worldwide impact because the clinical picture resembles many other febrile infections, and because of the limited capacity for bacteriological diagnosis in most areas of the developing countries owing to lack of funds. However, it has been possible to estimate the prevalence of TF in the world (Table 1)[6, 16]. For example, in Indonesia there were a mean of 900 000 cases per year and more than 20 000 deaths; 3-19-year-olds accounted for 91% of typhoid cases, with an attack rate of blood-culture positive TF of 1026 per 100 000 per year.

[TABULAR DATA OMITTED]

In the endemic areas of South America the age-specific incidence was:

- low in under-3-year-olds. However, an epidemiological study in Chile[7], based on the systematic collection of a single blood culture from all children younger than 24 months of age who were presented to health centres with fever, regardless of their other clinical symptoms, showed that 3.5% had an unrecognized bacteraemic infection due to S. typhi or S. pal-atyphi (in none was enteric fever suspected on clinical grounds); - high, with a peak among schoolchildren aged 5 to 19 years; - low in adults over 35 years of age.

Humans are the only natural hosts and reservoir. The infection is transmitted by ingestion of faecally contaminated food, vegetables or water, the highest incidence occurring where contaminated water supplies serve a large population. Epidemiological data suggest that waterborne transmission of S. typhi is usually a result of small inocula, whereas foodborne transmission is associated with large inocula and high attack rates.

The hypothesis that vegetables (irrigated with untreated waste waters) and fruit (freshened with contaminated river water) represent important vehicles of transmission in Chile explains the following epidemiological observations:

- the seasonal appearance of TF (in the summer when there is no rain and irrigation is used); - the low reported incidence of TF in young children (since raw vegetables are not an important food for them); - the high incidence of TF in high socioeconomic neighbourhoods (where salads are eaten in restaurants and at home); - the low incidence of TF in areas (e. …

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