Worm Infections in Children
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Worm Infections in Children Jill E. Weatherhead, MD,*† Peter J. Hotez, MD, PhD*† *Department of Pediatrics (Sections of Infectious Diseases and Tropical Medicine), National School of Tropical Medicine, Baylor College of Medicine, Houston, TX. †Sabin Vaccine Institute and Texas Children’s Hospital Center for Vaccine Development, Houston, TX. Educational Gaps 1. Clinicians should know that worm infections are among the most common pediatric infections in developing countries, led by intestinal helminth infections and schistosomiasis, and that these infections have chronic and disabling consequences for child growth and development. 2. Clinicians should know that some worm infections, such as toxocariasis and cysticercosis, are also common among children living in poverty in the United States and elsewhere in North America and Europe where, in some cases, they are important causes of epilepsy, cognitive impairments, and other illnesses. 3. Clinicians need a high index of suspicion for linking chronic disabilities in children to infections caused by worms. Objectives After completing the article, the reader should be able to: 1. Recognize the global burden of disease of worms in children. 2. Discuss the age-intensity distribution for worms in children. 3. Recognize the unique signs and symptoms of worm infections found predominantly in developing countries, such as intestinal helminth infections (ie, ascariasis, trichuriasis, hookworm infection) and schistosomiasis, as well as those also found widely in impoverished areas in North America and Europe, such as toxocariasis, enterobiasis, and cysticercosis. 4. Recognize the advantages and disadvantages of diagnostic modalities for helminth infections, schistosomiasis, toxocariasis, taeniasis, and cysticercosis. 5. Discuss and deliver recommended treatment regimens for intestinal helminth infections, schistosomiasis, toxocariasis, taeniasis, and AUTHOR DISCLOSURE Drs Weatherhead and Hotez have disclosed no financial cysticercosis in nonendemic and endemic countries. relationships relevant to this article. This commentary does contain a discussion of an unapproved/investigative use of a commercial product/device. Vol. 36 No. 8 AUGUST 2015 341 Downloaded from http://pedsinreview.aappublications.org/ at Health Sciences Library, Stony Brook University on September 30, 2015 INTRODUCTION estimates indicate that more than 800 million people have ascariasis, while approximately 450 million people each Worm infections (also known as helminth infections) are have trichuriasis or hookworm infection (hookworm). (4) considered among the most common diseases of children Moreover, an extremely common occurrence, especially for living in extreme poverty in the developing countries of a child, is simultaneous infection with two or even all three Asia, Africa, and Latin America. In addition, a surprising of these intestinal helminth infections. (4)(15) The number number of children in the United States and Europe are of children who harbor pinworm has not been determined. infected with worms. Hookworm leads the intestinal helminth infections in The major worm infections of children include the four DALYs and global disability because of their important role intestinal helminth infections of ascariasis, trichuriasis, in causing anemia. (16) Geographically, the largest number of hookworm,andenterobiasis,whicharetransmitted infected individuals lives in South Asia (ie, Indian sub- through contaminated soil; schistosomiasis, a water-borne continent), Southeast Asia, and East Asia, followed by infection associated with an aquatic snail intermediate host; sub-Saharan Africa and Latin America. (4) In terms of and toxocariasis and cysticercosis, two zoonotic infections specific countries, the greatest numbers of children with caused by larval stages of parasitic helminths. In total, these intestinal worms live in India, followed by Nigeria, Indo- worm infections rank among the leading global health nesia, and Bangladesh. (17) In all, an estimated 874.5 million threats to children. children require regular and periodic deworming in disease- GLOBAL IMPACT OF WORM INFECTIONS endemic countries. (18)(19) Schistosomiasis ranks just behind the intestinal hel- Worms are not major killers of children, even in developing minth infections as the most common worm infection. countries. According to a new estimate, fewer than 20,000 (2)(3) Approximately 250 million people are believed to be people die annually from the major pediatric helminth infected with schistosomes, although some experts have infections. (1) Instead, the importance of worms as contrib- suggested that the actual number of infections could be utors to global child health conditions is associated with much higher. (20) Almost all of the cases (99%) are due to their ability to cause chronic disability that often lasts Schistosoma haematobium, the cause of urinary tract schis- throughout childhood and adolescence. Over this period, tosomiasis, or S mansoni, the cause of intestinal schistoso- worms stunt growth, cause intellectual and cognitive defi- miasis. (5)(6) Unlike the intestinal helminth infections that cits, and produce damage to selected target organs such as occur worldwide, schistosomiasis is predominantly an Afri- the brain, liver, and urinary tract. Using a metric known as can disease. Today, more than 90% of schistosome infec- disability-adjusted life years (DALYs) (ie, the number of life tions occur in sub-Saharan Africa, with the largest number years lost either from premature death or disability), a recent in Nigeria, Ethiopia, and Democratic Republic of Congo. analysis by the Global Burden of Disease Study 2010 (5)(6) Of the approximately 250 million people who require determined that the major worm infections of children treatment for schistosomiasis, almost 50% are children. (Table 1) cause 9.0 million DALYs annually, a number (5)(6) Another important and unique feature of Shaematobium approximately equivalent to the DALYs caused by such infection is the increasing recognition that these particular conditions as measles, pertussis, pervasive development schistosomes affect the female genital tract to produce disorder, or rheumatic heart disease. (2)(3) female genital schistosomiasis, an ulcerative condition that Intestinal helminth infections, which are also known as is strongly associated with an increased risk of acquiring soil-transmitted helminth infections, represent the most human immunodeficiency virus (HIV)/AIDS. (7) common worm infections of children. These are led Two important larval worm infections are toxocariasis by ascariasis (Ascaris lumbricoides roundworm infection), and cysticercosis, both of which have been linked to epi- trichuriasis (Trichuris trichiura whipworm infection), and lepsy. (8)(13) The former is a zoonotic infection acquired hookworm infections (mostly caused by Necator americanus, from dogs or cats when humans accidentally swallow the with fewer than 25% of the infections caused either by eggs of the dog or cat roundworm, Toxocara canis or T cati, Ancylostoma duodenale or A ceylanicum or by mixed infec- respectively. Toxocariasis is widespread among children in tions) as well as pinworm infection (Enterobius vermicularis). both developing and developed countries, although there (15) Strongyloidiasis is a less common intestinal helminth are no precise estimates of the number of people infected. infection that also occurs among selected refugee popula- Large numbers of cases are found in Brazil, but it may also tions from Africa, Asia, and parts of Latin America and the be the most common worm infection in the United States, Caribbean. New Global Burden of Disease Study 2010 even exceeding pinworm. (9) Toxocariasis is more frequently 342 Pediatrics in Review Downloaded from http://pedsinreview.aappublications.org/ at Health Sciences Library, Stony Brook University on September 30, 2015 TABLE 1. Major Worm Infections of Children MAJOR SPECIES ESTIMATED LEADING GEOGRAPHIC DISABILITY-ADJUSTED DISEASE IN HUMANS NUMBER OF CASES AREAS OR COUNTRIES LIFE YEARS (DALYs) REFERENCES Intestinal >1 billion Asia 5.2 million 2, 3 Helminth Infections Ascariasis Ascaris 819 million South Asia 1.3 million 2, 3, 4 lumbricoides East Asia Trichuriasis Trichuris trichiura 465 million Southeast Asia 0.6 million 2, 3, 4 South Asia Hookworm Necator 439 million South Asia 3.2 million 2, 3, 4 infection americanus Southeast Asia Strongyloidiasis Strongyloides Not determined East Africa Not determined stercoralis Southeast Asia Enterobiasis Enterobius Not determined Worldwide Not determined vermicularis North America Schistosomiasis Schistosoma 252 million Sub-Saharan Africa 3.3 million 2, 3, 5, 6, 7 haematobium Schistosoma mansoni Toxocariasis Toxocara canis Not determined Worldwide Not determined 8, 9, 10, 11, 12 North America Taeniasis/ Taenia solium 1.4 million cases of Latin America 0.5 million 13, 14 Cysticercosis epilepsy Sub-Saharan Africa South Asia Total 2 billion Asia, Sub-Saharan Africa 9.0 million found in the southern United States and in degraded urban shown in Figure 1, with some exceptions, the intensity of environments, where it is a health disparity disproportionately each of the major helminth infections primarily peaks in affecting African American populations. (9) In addition to school-age children or adolescents. The basis for this age- epilepsy and cognitive delays, (10) the disease has been linked dependent predilection is not well understood, and different to reduced lung function and even asthma. (11)(12)