Hookworm infection is caused by the nematode parasites Necator americanus and organisms within the genus Ancylostoma. Soil-transmitted helminths (STHs) include:

- N. americanus (primary organism that causes hookworm infection)
- A. duodenale
- Roundworm
- Ascaris lumbricoides
- Trichuris trichiura 


Etiology of Hookworm

The global disease burden, as analyzed through disability-adjusted life years, overwhelmingly exceeds other tropical diseases other than malaria, leishmaniasis and lymphatic filariasis. Hookworm infections are correlated with increased school absences and, as a result, a decreased future socioeconomic productivity. This research reflects that hookworm, similar to other NTDs, promotes long-term disability and increases the likelihood that a marginalized population will remain in impoverished conditions. 

Global Disease Burden of Hookworm

This parasitic infection results from the exposure of infective larval stages through the skin. Following entry of the pathogen, the larvae travel through the body to the lungs before ending in the gastrointestinal tract. The worms reproduce to form more than 30,000 eggs per day, which exit the host through the expulsion of feces. 

Clinical Features of Hookworm

Despite a lack of surveillance mechanisms, extensive review of literature places the number of global cases as approximately 740 million people since 1990. The highest prevalence occurs in sub-Saharan Africa and eastern Asia. Higher transmission rates are correlated with impoverished areas in southern China, the Indian subcontinent and the Americas. The neglected status of hookworm is associated with high hookworm prevalence rates among the world’s poorest populations. 

Global Distribution of Hookworm

Hookworm morbidity is proportional to the number of adult parasites inhabiting the patient. The severity of infection is determined through quantitative fecal egg counts and ranges from modern infections to heavily intense infections. 
- Moderate-intensity infections: 2,000-3,999 eggs per gram of feces
- Heavy-intensity infections: 4,000 or more eggs per gram of feces

Unlike other STH infections, hookworm infections portray an age-intensity profile where the severity of disease rises with age or plateaus in adulthood. Although this is largely observed in patients, the biological basis for this phenomenon is unknown. 


Epidemiology of Hookworm

Current control strategies target the reduction of morbidity rates through mass treatments (deworming) of populations afflicted with the parasite. These mass drug campaigns include the distribution of anthelmintic drugs, benzimidazoles (BZAs), levamisole and pyrantel. Continued investment in deworming should be complemented by sanitation and access to safe drinking water. The World Health Organization has led campaigns to distribute doses of these drugs to schools with the highest rates of STH infections. The deworming of students has many health benefits including: 
- Improved iron and hemoglobin levels
- Physical growth and fitness
- Cognition

There are also a number of societal benefits including 
- Advancements in education
- Reduced community transmission of ascaris and trichuris infections


Hookworm Control Strategies

The Human Hookworm Vaccine Initiative (HHVI) is in the process of developing a functional and safe vaccine. HHVI is a non-profit collaboration at the George Washington University, London School of Hygiene and Tropical Medicine and the Oswaldo Cruz Foundation (vaccine development has been sponsored by the Sabin Vaccine Institute). Hookworm vaccine development involves research, process development, vaccine manufacturing and control and pre-clinical/clinical testing. 

Na-ASP-2 Hookworm Vaccine

Adult hookworms may destroy the host through intestinal hemorrhage. These parasites ingest the blood rupturing erythrocytes and degrading hemoglobin in the process. Hookworm infections cause the disease silent blood loss, which leads to anemia and malnutrition. Generally, there is a positive correlation between parasite population and destruction of RBCs in the host (women of reproductive age, children and other populations with low iron). In children, chronic infections may lead to growth retardation and cognitive impairments. Infections in pregnant women may lead to negative maternal-fetal outcomes. 

Progression of Hookworm Infection

Hookworms are parasitic worms that infect the small intestine, with the highest prevalence in sub-Saharan Africa and eastern Asia. 

Georgetown University

- *Ascaris lumbricoides*
- *Necator americanus*
- *Enterobius vermicularis*
- *Toxocara canis* and *T. cati*
- *Trichinella spiralis*
- *Dirofilaria immitis*

Parasitic species of Roundworms (Nematodes)

Centers for Disease Control and Prevention. (n.d.). Centers for Disease control and Prevention. Centers for Disease Control and Prevention. https://www.cdc.gov/. 

Centers for Disease Control and Prevention

Hookworm: “The Great Infection of Mankind”
Hotez PJ, Bethony J, Bottazzi ME, Brooker S, Buss P (2005) Hookworm: “The Great Infection of Mankind”. PLOS Medicine 2(3): e67. https://doi.org/10.1371/journal.pmed.0020067

Hookworm: "The Great Infection of Mankind"

Hookworm

*Ascaris lumbricoides* is the largest intestinal roundworm and is a widespread parasite across the world.

*Ascaris lumbricoides*

*Enterobius vermicularis*, more commonly known as pinworm, is the most common nematode parasitic infection in the United States.

*Enterobius vermicularis*

*Necator americanus*, more commonly known as hookworm, is a common nematode parasitic infection, this specific species of hookworm is associated with having North American origins. 

*Necator americanus*

*Toxocara canis* and *T. cati* are the causative nematodes for toxocariasis infections, which can be transmitted from dogs/cats to humans. 

 *Toxocara canis* and *T. cati*

*Trichinella spiralis* is the causative nematode for trichinellosis, or trichinosis, infections, which can be contracted by consuming undercooked meat.

*Trichinella spiralis*

*Dirofilaria immitis*, more commonly known as heartworm, is transmitted to dogs/cats through mosquitoes.

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