Spatial and Genetic Epidemiology of Hookworm in a Rural Community in Uganda

1. Spatial and Genetic Epidemiology of Hookworm in a Rural Community in Uganda Holly Dorchak Bio 4800 Symbiotic Interactions March 17, 2011

2. Hookworms • 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

3. Why are some hosts more heavily infected than others? • Differences in exposure to parasites? • Genetic predisposition/immunity? • Age? • Sex? • Size? • Diet? • Intraspecific interactions of parasites? • Interspecific interactions of parasites? • This study looked at whether genetics or exposure related factors had a larger effect on the intensity of hookworm infection

4. The 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

5. The 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

6. Results • 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 vsold • Gender: male vs female • Anthelmintic treatment vsno treatment • Socio-economic/exposure factors: • barefeetvs shoes • household head with education vsno education • latrine vs no latrine • earth floor vs cement • formal income vsno formal income

7. Prevalence of infection (%) • closed circles=males • open circles-=females Mean infection intensity (epg)

8. Why are some hosts more heavily infected than others? • Differences in exposure to parasites • Genetic predisposition/immunity • Age • Sex? • Size??? • Diet??? • Intraspecific interactions of parasites??? • Interspecific interactions of parasites? • This study looked at whether genetics or exposure related factors had a larger effect on the intensity of hookworm infection

9. Conclusions • 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

10. References Pullan, 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.