Genetic and household determinants of predisposition to human hookworm infection in a Brazilian community.
BACKGROUND
Predisposition to heavy or light human hookworm infection is consistently reported in treatment-reinfection studies. A significant role for host genetics in determining hookworm infection intensity has also been shown, but the relationship between host genetics and predisposition has not been investigated.


METHODS
A treatment-reinfection study was conducted among 1302 individuals in Brazil. Bivariate variance components analysis was used to estimate heritability for pretreatment and reinfection intensity and to estimate the contribution of genetic and household correlations between phenotypes to the overall phenotypic correlation (ie, predisposition).


RESULTS
Heritability for hookworm egg count was 17% before treatment and 25% after reinfection. Predisposition to heavy or light hookworm infection was observed, with a phenotypic correlation of 0.34 between pretreatment and reinfection intensity. This correlation was reduced to 0.23 after including household and environmental covariates. Genetic and household correlations were 0.41 and 1, respectively, and explained 88% of the adjusted phenotypic correlation.


CONCLUSIONS
Predisposition to human hookworm infection in this area results from a combination of host genetics and consistent differences in exposure, with the latter explained by household and environmental factors. Unmeasured individual-specific differences in exposure did not contribute to predisposition.
Quinnell
Rupert J
RJ
Institute of Integrative and Comparative Biology, University of Leeds, Leeds, United Kingdom. R.J.Quinnell@leeds.ac.uk
Pullan
Rachel L
RL
Breitling
Lutz Ph
LP
Geiger
Stefan M
SM
Cundill
Bonnie
B
Correa-Oliveira
Rodrigo
R
Brooker
Simon
S
Bethony
Jeffrey M
JM
D000293:Adolescent; D000328:Adult; D000368:Aged; D000818:Animals; D001938:Brazil; D002648:Child; D002675:Child, Preschool; D005192:Family Health; D020022:Genetic Predisposition to Disease; D006725:Hookworm Infections / Q000453:epidemiology* / Q000235:genetics* / Q000635:transmission; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D010270:Parasite Egg Count; D012307:Risk Factors; D055815:Young Adult