Mild hookworm infection is usually asymptomatic. Heavy infection may result in iron deficiency anaemia and hypoproteinaemia, as a result of blood loss. Hookworm infestation may also result in local or generalised allergic reactions or abdominal pain.
Ancylostoma duodenale and Necator americanus are the main nematodes causing hookworm infection in man. Almost eradicated from Europe and the USA, hookworm infection is still seen in warm, moist climates in tropical and sub–tropical regions between 45o N and 35o S of the equator (e.g., Asia, Africa, Central and South America and the South Pacific). The geographic distribution of these two hookworms used to be regarded as relatively distinct, the former being more prevalent in Europe and south–western Asia, and the latter in tropical Africa and in the Americas. However, over the past decades, both parasites have become widely distributed throughout the tropics and sub–tropics, and rigid demarcations are no longer tenable. It is estimated that the global prevalence of hookworm infection is about 900 million cases i.e., almost one–fourth of the world’s population. The annual number or deaths may be approximately 50,000 as a result of hookworm anemia.
Hookworm infection is widely prevalent in India. Necator americanus is predominant in south India, and Ancylostoms duodenal in north India. Recently, another species, A. ceylanicum has been reported from a village near Calcutta. The heavily infected areas are found in Assam (tea gardens), West Bengal, Bihar, Orissa, Andhra Pradesh, Tamil Nadu, Kerala and Maharashtra. More than 200 million people are estimated to be infected in India. It is believed that 60 to 80 per cent of the population of certain areas of West Bengal, UP, Bihar, Orissa, Punjab, and the eastern coast of Tamil Nadu and Andhra Pradesh are infected with hookworms.
Morbidity and mortality from hookworm infection depend much on the worm load. Chandler worked out an index on the basis of an average number of hookworm eggs per gram of feces for the entire community, which is as below:
Average number of eggs per gram of stool
|Below 200||Hookworm is not of much significance|
|200–250||May be regarded as potential danger|
|250–300||Minor public health problem|
|Above 300||Important public health problem|
Chandler’s index is still used in epidemiological studies of hookworm disease. By this index, worm loads in different population groups can be compared and also the degree of reduction of egg output after mass treatment.