Resistance to reinfection with Schistosoma mansoni in occupationally exposed adults and effect of HIV-1 co-infection on susceptibility to schistosomiasis: a longitudinal study.
BACKGROUND
Previous studies have reported age-dependent development of resistance to reinfection by schistosomes and identified immunological correlates of this resistance. However, whether resistance exists that is independent of age effects has been questioned. We did a longitudinal investigation of reinfection by Schistosoma mansoni in an adult population with high occupational exposure.


METHODS
We monitored a cohort of 96 male car washers working along the shores of Lake Victoria, Kenya during 349.7 person-years for frequency of water contact and infection with S mansoni. Patients were treated with praziquantel upon study entry and after reinfection with S mansoni. Bivariate analyses and a multivariate proportional hazards model were used to assess the effects of water contact, previous infections, and HIV-1 on S mansoni reinfection rates.


RESULTS
13 car washers did not get reinfected or only became reinfected after an extended time (91 weeks). 47 initially had a short time to reinfection (15 weeks) but on subsequent treatments showed increased time to reinfection (29-38 weeks). 36 consistently displayed short times to reinfection (<15 weeks) despite multiple reinfection and treatment cycles. Decreased CD4 T-cell counts in HIV-1-positive individuals corresponded to increased susceptibility to S mansoni reinfection.


CONCLUSIONS
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.
Karanja
Diana M S
DM
Centre for Vector Biology and Control Research, Kenya Medical Research Institute, Kisumu, Kenya.
Hightower
Allen W
AW
Colley
Daniel G
DG
Mwinzi
Pauline N M
PN
Galil
Karin
K
Andove
Julius
J
Secor
W Evan
WE
D000328:Adult; D000367:Age Factors; D000818:Animals; D018791:CD4 Lymphocyte Count; D004198:Disease Susceptibility / Q000276:immunology; D015658:HIV Infections / Q000150:complications* / Q000276:immunology; D015497:HIV-1; D006801:Humans; D007109:Immunity / Q000276:immunology; D007113:Immunity, Innate; D008137:Longitudinal Studies; D008297:Male; D015999:Multivariate Analysis; D016273:Occupational Exposure; D016016:Proportional Hazards Models; D012550:Schistosoma mansoni / Q000276:immunology*; D012555:Schistosomiasis mansoni / Q000150:complications* / Q000276:immunology*; D014867:Water / Q000469:parasitology*
D014867:Water