Researchers from Kenya and the USA investigated reinfection by Schistosoma mansoni in an adult population with high occupational exposure.
A total of 96 male car washers, working along the shores of Lake Victoria, Kenya, were included in the study. The frequency of water contact and infection with S. mansoni were evaluated.
Patients were treated with praziquantel upon study entry and after reinfection with S. mansoni.
The effects of water contact, previous infections, and HIV-1 on S. mansoni reinfection rates were all assessed.
Of the car washers, 13 did not get reinfected, or only became reinfected after an extended time (91 weeks).
However, 47 initially had a short time to reinfection (15 weeks) but on subsequent treatments showed increased time to reinfection (29-38 weeks).
| CD4 T cells may contribute to resistance to reinfection with S. mansoni.
A further 36 consistently displayed short times to reinfection (less than 15 weeks) despite multiple reinfection and treatment cycles.
The team found that decreased CD4 T-cell counts in HIV-1-positive individuals corresponded to increased susceptibility to S. mansoni reinfection.
Diana M. S. Karanja, of the Kenya Medical Research Institute, Kisumu, Kenya, said on behalf of her colleagues, "Adults similarly exposed to schistosomiasis are either resistant to reinfection; susceptible, but develop resistance to reinfection after multiple treatments; or remain susceptible to reinfection.
"Thus, immunological resistance to reinfection with S. mansoni exists or can develop independent of age effects."
"The consequence of HIV-1 co-infection suggests that CD4 T cells contribute to this resistance," she concluded.