Neglected Tropical Disease Control and Elimination
STHs are a group of nematode worms transmitted through soil contaminated with infected human faeces. Of particular importance are the roundworm Ascaris lumbricoides, the whipworm Trichuris trichiura (figure 2) and the hookworm Necator americanus. Most STH infections result from ingestion of contaminated soil, although hookworms are able to penetrate the skin when in contact with contaminated soil. These STHs are practically ubiquitous in areas of extreme poverty in Africa, Asia and Latin America, with the largest numbers of cases occurring among the extreme poor living in some of the large low- to middle-income countries of Asia, such as Bangladesh, China, India and Indonesia. Based on transmission dynamic studies, children suffer from the highest intensity of Ascaris and Trichuris infections, whereas hookworm intensities can be high among both children and adults. Based on the Preventive Chemotherapy Databank, maintained by WHO, we have calculated that in 2011 875 million children lived in high-risk areas worldwide, of whom about 30% are preschool age children and 70% school age children. STH infections impair the nutritional status of the infected child and, in the case of hookworm, are responsible for blood loss, leading to iron-deficiency anaemia. In sub-Saharan Africa alone an estimated 50 million school-aged children are infected with hookworm. Infection with STHs has been associated with significant impairment in growth and physical development. Additionally, mounting evidence suggests that cognitive development is also impaired. Adding to the burden of disease from STH infection is the finding that in Africa and elsewhere these helminth infections overlap geographically with malaria to produce high rates of STH–malaria co-infection and severe anaemia.
(Enlarge Image)
Figure 2.
Rectal prolapse due to trichuriasis. In heavy infections with Trichuris trichiura, adult worms can extend throughout the length of the colon down to the rectum. Over time, inflammation in the rectum causes tenesmus leading to prolapse. Notice here the significant number of worms seen on the rectal mucosal lining. Image courtesy of the Public Health Image Library, Centers for Disease Control and Prevention.
Schistosomiasis (also known as bilharziasis and snail fever) is a chronic infection of the parasitic blood flukes known as schistosomes. Schistosomes are able to penetrate the skin when a person is in contact with water containing the infected snail intermediate host. Children and adolescents are increasingly being recognised as important factors in environmental transmission as these infected populations shed a large number of eggs and they have frequent contact with water sources, both in bathing and in play (figure 3). Most commonly, infection is caused by Schistosoma haematobium and Schistosoma mansoni, which result in urogenital schistosomiasis and intestinal schistosomiasis, respectively. More than 90% of schistosomiasis cases today occur in Africa. Using numbers from the Preventive Chemotherapy Databank we have calculated that in 2011, 243 million people lived in high-risk areas, including 112 million school age children, predominantly in sub-Saharan Africa. However, some investigators have suggested that these numbers are underestimates based on a considerable number of children who are egg-negative at the time of diagnosis. Thus, some investigators have suggested that 400 million or more people are infected. There is increasing recognition that children with chronic schistosomiasis suffer from a syndrome of chronic inflammation, pain and anaemia that interferes with child growth and development, similar to some of the manifestations in STH infections. Infection in the infant and preschool age groups is also increasingly being recognised and documented. New evidence suggests that early childhood infection with schistosomiasis predisposes to increased morbidity later in life than an infection acquired in adulthood. Indeed, adolescents have been found to have surprisingly intense infections. In adolescents and young adults infected with S haematobium, schistosome granulomas can form in the female genital tract, leading to female urogenital schistosomiasis (FUGS), which today may be one of the most common gynaecological conditions of African girls. FUGS has also been linked to increased susceptibility to HIV infection, especially in southeastern Africa.
(Enlarge Image)
Figure 3.
Children at play in a river in Puerto Rico, despite the sign on the bank warning 'Danger—There is Bilharzia', another name for schistosomiasis. Over 112 million school age children live in high-risk areas, predominantly in sub-Saharan Africa. Image courtesy of the Public Health Image Library, Centers for Disease Control and Prevention.
Trachoma is an infection with the bacteria Chlamydia trachomatis. Infection occurs when eyes are inoculated with infected ocular discharge, resulting in a self-limiting episode of conjunctivitis. WHO estimates that in 2010, 325 million people lived in areas endemic for C trachomatis, and more than 21 million people were actively infected. In hyperendemic areas, 90% of preschool age children may be infected. Younger children are at higher risk of severe infection with a longer duration period. Multiple re-infections during childhood causes inflammation that can result in conjunctival scarring. Once scarring of the conjunctiva occurs, the eyelid alignment is altered, pulling the margin inwards. This can result in trichiasis, when the eyelashes rub onto the globe, causing trauma to the cornea. Approximately 3% of all cases of blindness worldwide are caused by trachoma.
LF is a debilitating infection caused by the filarial worms Wuchereria bancrofti, Brugia malayi or Brugia timori, all transmitted by mosquito vectors. Based on the Preventive Chemotherapy Databank, we have calculated that in 2011 there were 1.41 billion people living in high-risk areas for infection. Long thought to be an exclusive infection of adulthood, LF is now recognised to be an infection often contracted in childhood, with early manifestations of lymphatic obstruction, filarial fevers, and in some cases hydrocele and lymphoedema. Children under 10 years of age have prevalence rates around 30% of the adult prevalence rates, while those 10–19-years-old have approximately 69% of the adult prevalence rate. The adult worms reside in the lymphatic system, which can result in lymphoedema sometimes so severe that it is referred to as 'elephantiasis'. More than 40 million people have clinically apparent LF. Vector control programmes generally have limited success, with a few exceptions such as in the Solomon Islands where long-term dichlorodiphenyltrichloroethane (DDT) spraying during the Malaria Eradication Campaign led to eradication of W bancrofti.
Onchocerciasis, also known as 'river blindness', is caused by the filarial nematode Onchocerca volvulus. In most onchocerciasis-endemic communities in sub-Saharan Africa, the disease disproportionately affects adults. However, the rate of infection among adolescents is often high and community directed treatments typically include children. In contrast, the prevalence among young and preschool age children is often low. It has been noted that children of onchocerca infected mothers are more likely to become infected at a younger age.
The Problem: NTDs in Children
STH Infection
STHs are a group of nematode worms transmitted through soil contaminated with infected human faeces. Of particular importance are the roundworm Ascaris lumbricoides, the whipworm Trichuris trichiura (figure 2) and the hookworm Necator americanus. Most STH infections result from ingestion of contaminated soil, although hookworms are able to penetrate the skin when in contact with contaminated soil. These STHs are practically ubiquitous in areas of extreme poverty in Africa, Asia and Latin America, with the largest numbers of cases occurring among the extreme poor living in some of the large low- to middle-income countries of Asia, such as Bangladesh, China, India and Indonesia. Based on transmission dynamic studies, children suffer from the highest intensity of Ascaris and Trichuris infections, whereas hookworm intensities can be high among both children and adults. Based on the Preventive Chemotherapy Databank, maintained by WHO, we have calculated that in 2011 875 million children lived in high-risk areas worldwide, of whom about 30% are preschool age children and 70% school age children. STH infections impair the nutritional status of the infected child and, in the case of hookworm, are responsible for blood loss, leading to iron-deficiency anaemia. In sub-Saharan Africa alone an estimated 50 million school-aged children are infected with hookworm. Infection with STHs has been associated with significant impairment in growth and physical development. Additionally, mounting evidence suggests that cognitive development is also impaired. Adding to the burden of disease from STH infection is the finding that in Africa and elsewhere these helminth infections overlap geographically with malaria to produce high rates of STH–malaria co-infection and severe anaemia.
(Enlarge Image)
Figure 2.
Rectal prolapse due to trichuriasis. In heavy infections with Trichuris trichiura, adult worms can extend throughout the length of the colon down to the rectum. Over time, inflammation in the rectum causes tenesmus leading to prolapse. Notice here the significant number of worms seen on the rectal mucosal lining. Image courtesy of the Public Health Image Library, Centers for Disease Control and Prevention.
Schistosomiasis
Schistosomiasis (also known as bilharziasis and snail fever) is a chronic infection of the parasitic blood flukes known as schistosomes. Schistosomes are able to penetrate the skin when a person is in contact with water containing the infected snail intermediate host. Children and adolescents are increasingly being recognised as important factors in environmental transmission as these infected populations shed a large number of eggs and they have frequent contact with water sources, both in bathing and in play (figure 3). Most commonly, infection is caused by Schistosoma haematobium and Schistosoma mansoni, which result in urogenital schistosomiasis and intestinal schistosomiasis, respectively. More than 90% of schistosomiasis cases today occur in Africa. Using numbers from the Preventive Chemotherapy Databank we have calculated that in 2011, 243 million people lived in high-risk areas, including 112 million school age children, predominantly in sub-Saharan Africa. However, some investigators have suggested that these numbers are underestimates based on a considerable number of children who are egg-negative at the time of diagnosis. Thus, some investigators have suggested that 400 million or more people are infected. There is increasing recognition that children with chronic schistosomiasis suffer from a syndrome of chronic inflammation, pain and anaemia that interferes with child growth and development, similar to some of the manifestations in STH infections. Infection in the infant and preschool age groups is also increasingly being recognised and documented. New evidence suggests that early childhood infection with schistosomiasis predisposes to increased morbidity later in life than an infection acquired in adulthood. Indeed, adolescents have been found to have surprisingly intense infections. In adolescents and young adults infected with S haematobium, schistosome granulomas can form in the female genital tract, leading to female urogenital schistosomiasis (FUGS), which today may be one of the most common gynaecological conditions of African girls. FUGS has also been linked to increased susceptibility to HIV infection, especially in southeastern Africa.
(Enlarge Image)
Figure 3.
Children at play in a river in Puerto Rico, despite the sign on the bank warning 'Danger—There is Bilharzia', another name for schistosomiasis. Over 112 million school age children live in high-risk areas, predominantly in sub-Saharan Africa. Image courtesy of the Public Health Image Library, Centers for Disease Control and Prevention.
Trachoma
Trachoma is an infection with the bacteria Chlamydia trachomatis. Infection occurs when eyes are inoculated with infected ocular discharge, resulting in a self-limiting episode of conjunctivitis. WHO estimates that in 2010, 325 million people lived in areas endemic for C trachomatis, and more than 21 million people were actively infected. In hyperendemic areas, 90% of preschool age children may be infected. Younger children are at higher risk of severe infection with a longer duration period. Multiple re-infections during childhood causes inflammation that can result in conjunctival scarring. Once scarring of the conjunctiva occurs, the eyelid alignment is altered, pulling the margin inwards. This can result in trichiasis, when the eyelashes rub onto the globe, causing trauma to the cornea. Approximately 3% of all cases of blindness worldwide are caused by trachoma.
LF and Onchocerciasis
LF is a debilitating infection caused by the filarial worms Wuchereria bancrofti, Brugia malayi or Brugia timori, all transmitted by mosquito vectors. Based on the Preventive Chemotherapy Databank, we have calculated that in 2011 there were 1.41 billion people living in high-risk areas for infection. Long thought to be an exclusive infection of adulthood, LF is now recognised to be an infection often contracted in childhood, with early manifestations of lymphatic obstruction, filarial fevers, and in some cases hydrocele and lymphoedema. Children under 10 years of age have prevalence rates around 30% of the adult prevalence rates, while those 10–19-years-old have approximately 69% of the adult prevalence rate. The adult worms reside in the lymphatic system, which can result in lymphoedema sometimes so severe that it is referred to as 'elephantiasis'. More than 40 million people have clinically apparent LF. Vector control programmes generally have limited success, with a few exceptions such as in the Solomon Islands where long-term dichlorodiphenyltrichloroethane (DDT) spraying during the Malaria Eradication Campaign led to eradication of W bancrofti.
Onchocerciasis, also known as 'river blindness', is caused by the filarial nematode Onchocerca volvulus. In most onchocerciasis-endemic communities in sub-Saharan Africa, the disease disproportionately affects adults. However, the rate of infection among adolescents is often high and community directed treatments typically include children. In contrast, the prevalence among young and preschool age children is often low. It has been noted that children of onchocerca infected mothers are more likely to become infected at a younger age.