Spatial and Genetic Spatial and Genetic EpidemiologyEpidemiology

of Hookworm in a Rural of Hookworm in a Rural Community in UgandaCommunity in Uganda

Holly DorchakBio 4800

Symbiotic InteractionsMarch 17, 2011

HookwormsHookworms•Nematode

•Geohelminth

•L3 larvae penetrate skin (active transmission)

•‘Bronchiole-tracheal escalator’

•Can cause anemia

•Affects 600 million people worldwide

•2 main hookworms: Necator americanus and Ancylostoma duodenale

•Differences in exposure to parasites?•Genetic predisposition/immunity?•Age? •Sex?•Size?•Diet?•Intraspecific interactions of parasites?•Interspecific interactions of parasites?

Why are some hosts more Why are some hosts more heavily infected than others?heavily infected than others?

•This study looked at whether genetics or exposure related factors had a larger effect on the intensity of hookworm infection

The StudyThe Study•School based de-worming exists but there is still a need for refinement, by doing epidemiological studies high risk individuals can be determined and treated•1803 individuals from rural community in Uganda•Individuals were 6 months-85 years old•Census, questionnaires and mapping to determine household demographics, socio-economic status, distance from health care, previous anthelmintic treatment, relatedness within villages

The StudyThe Study•Fecal samples were microscopically analyzed for eggs

-This is a way to indirectly look at worm count-Problems: intraspecific competition-lightly infected hosts tend

to have parasites that produce more eggs than in heavily infected hosts

:egg production can also change through out the day

•Used negative binomial spatial modelling and genetic variance component analysis to determine the contribution of genetics and exposure related factors to intensity variation

ResultsResults•39.3% of individuals were infected•87.7% of individuals had light infections (less than 1000 epg) •Hookworm infection was over-dispersed-light infection in many individuals and high infection in only a few individuals •Rarely found other helminths (no interspecific interactions)

•Age: young vs old•Gender: male vs female•Anthelmintic treatment vs no treatment•Socio-economic/exposure factors:•barefeet vs shoes•household head with education vs no education•latrine vs no latrine•earth floor vs cement•formal income vs no formal income

•closed circles=males•open circles-=females

Prevalence of infection (%)

Mean infection intensity (epg)

Why are some hosts more Why are some hosts more heavily infected than others?heavily infected than others?

•This study looked at whether genetics or exposure related factors had a larger effect on the intensity of hookworm infection

ConclusionsConclusions•Heritability accounted for only 11% of variability in egg counts•Spatial clustering of infection suggests that exposure occurs within or near households •Despite school based deworming parasite infection is still high, particularly in adults•Exposure related factors have a greater effect on infection intensity than host genetics

ReferencesReferencesPullan, R. L., Kabatereine, N. B., Quinnell, R. J., Brooker, S. (2010). Spatial and genetic epidemiology of hookworm in a rural

community in uganda. Plos Negl Trop Dis. 4(6):e713.

Anderson, R. M., May, R. M. (1978). Regulation and stability of host- parasite population interactions: I. Regulatory processes. J. Animal Ecology. 47(1): 219-247.