In a study published in Nature Genetics (10 November), it found that a certain type of allele of the HLA-DRB1 gene is associated with the natural resistance of an individual against typhoid fever, also called enteric fever. Blood samples taken in Vietnam and Nepal, showed that five and four per cent of their population, respectively, were resistant to the bacterial disease.
The study analysed 432 individuals infected with typhoid fever and 2,011 healthy individuals in Vietnam and 595 individuals with typhoid fever and 386 healthy individuals in Nepal.
Globally, there are 26.9 million new cases every year of typhoid fever caused by Salmonella typhi and paratyphoid fever caused by Salmonella paratyphi due to the consumption of food or water contaminated with faeces.
“We found that carrying a particular form of the HLA-DRB1 gene provides natural resistance against typhoid fever. This gene code for a receptor is important in the immune response by recognising proteins from invading bacteria,” says Sarah Dunstan, the lead author of the study and a senior researcher at the Oxford University Clinical Research Unit in Vietnam.
“This is the first time a human gene has been shown to provide resistance against typhoid. If we can understand the mechanisms behind this natural resistance to typhoid, we can try and mimic this effect when developing new, improved vaccines against typhoid fever,” Dunstan tells SciDev.Net.
Dunstan says the current licensed vaccine for typhoid is only moderately effective and does not protect against paratyphoid fever, which is now increasing across Asia.
Sri Budiarti, a medical microbiologist from the biology department of Bogor Agricultural University, Indonesia, adds that the current vaccines are not effective in suppressing typhoid cases in Asia because there are too many strains of Salmonella bacteria that can infect a human.
“The current vaccines are only effective for a few types of typhoid bacteria so it is really difficult to cope with typhoid cases. The discovery of this gene is promising as it provides a natural mechanism against typhoid fever from the human side,” says Budiarti.
But she reminds that aside from vaccine development, suppression of typhoid fever should also be accompanied by improved sanitation in developing countries.
Link to citation results in Nature Genetics.
This article has been produced by SciDev.Net's South-East Asia & Pacific desk.