Epidemiology
It is estimated that between 576-740 million individuals are infected with hookworm today. Of these infected individuals, about 80 million are severely affected. The major etiology of hookworm infection is N. Americanus which is found the Americas, sub-Saharan Africa, and Asia. A. duodenale is found in more scattered focal environments, namely Europe and the Mediterranean. Most infected individuals are concentrated in sub-Saharan Africa and East Asia/the Pacific Islands with each region having estimates of 198 million and 149 million infected individuals, respectively. Other affected regions include: South Asia (50 million), Latin America and the Caribbean (50 million), South Asia (59 million), Middle East/North Africa (10 million). A majority of these infected individuals live in poverty-stricken areas with poor sanitation. Hookworm infection is most concentrated among the world’s poorest who live on less than $2 a day.
Many of the numbers regarding the prevalence of hookworm infection are estimates as there is no international surveillance mechanism currently in place to determine prevalence and global distribution. Some prevalence rates have been measured through survey data in endemic regions around the world. The following are some of the most recent findings on prevalence rates in regions endemic with hookworm.
Darjeeling, Hooghly District, West Bengal, India (Pal et al. 2007)
• 42.8% infection rate of predominantly N. Americanus although with some A. Duodenale infection
• Both hookworm infection load and degree of anemia in the mild range
Xiulongkan Village, Hainan Province, China (Gandhi et al. 2001)
• 60% infection rate of predominantly N. Americanus
• Important trends noted were that prevalence increased with age (plateau of about 41 years) and women had higher prevalence rates than men
Hoa Binh, Northwest Vietnam (Verle et al. 2003)
• 52% of a total of 526 tested households infected
• Could not identify species, but previous studies in North Vietnam reported N. Americanus in more than 95% of hookworm larvae
Minas Gerais, Brazil (Fleming et al. 2006)
• 62.8% infection rate of predominantly N. Americanus
KwaZulu-Natal, South Africa (Mabaso et al. 2004)
• Inland areas had a prevalence rate of 9.3% of N. Americanus
• Coastal plain areas had a prevalence rate of 62.5% of N. Americanus
There have also been recent technological developments that will hopefully facilitate more accurate mapping of hookworm prevalence. Some researchers have begun to use geographical information systems (GIS) and remote sensing (RS) to examine helminth ecology and epidemiology. Brooker et al. utilized this technology to create helminth distribution maps of sub-Saharan Africa. By relating satellite derived environmental data with prevalence data from school-based surveys, they were able to create detailed prevalence maps. The study focused on a wide range of helminths, but interesting conclusions about hookworm specifically were found. As compared to other helminths, hookworm is able to survive in much hotter conditions and was highly prevalent throughout the upper end of the thermal range. Hopefully this information along with more detailed prevalence maps can lead to more effective public health measures.
Improved molecular diagnostic tools are another technological advancement that could help improve existing prevalence statistics. Recent research has focused on the development of DNA-based tool that can be used for diagnosis of infection, specific identification of hookworm, and analysis of genetic variability in hookworm populations. Again this can serve as a major tool for different public health measures against hookworm infection. Most research regarding diagnostic tools is now focused on the creation of a rapid and cost-effective assay for the specific diagnosis of hookworm infection. Many are hopeful that its development can be achieved within the next 5 years.
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