How Common Are Parasites?

Table of Contents

1. What the Presentation Said
2. How Parasite Numbers Are Counted
3. Intestinal Worms Worldwide
4. Schistosomiasis and Malaria
5. Death and Disability: The Global Burden Figures
6. Parasites in the United States
7. Hookworm and the American South
8. Parasites in Europe and the Blastocystis Question
9. Food- and Water-Borne Protozoa
10. Are Parasites Missed in Wealthy Countries?
11. How the Claim Compares With the Research
12. What Is Not Known
13. Connections
14. Key Research Papers
15. Featured Videos

What the Presentation Said

The presentation opened by calling parasites an "invisible epidemic". The speaker's reasoning was that many parasites are microscopic, or stay hidden inside the body until they appear in the stool, so most infections go unseen.

The speaker then made four points about how common parasites are:

• A world count. The speaker said that over 3 million people in the world harbour parasites, and that the true number could be greater, because the figure covers only what is reported or known.
• Under-diagnosis in developed countries. The speaker said infections are often under-diagnosed in developed countries.
• Everywhere, not only the tropics. The speaker said parasites are found not only in Africa, South America, Mexico and Asia, but also in Switzerland, Germany, New York City and every place in the world.
• A burden map. The speaker showed a world map of the impact of parasitic diseases, said it came from World Health Organization data from about 2004, and said that in some places more than half a year of life per person is lost every year to death or disability from parasitic infections. The speaker added that the data are 22 years old and suggested the problem may be even larger in 2026.

The same opening section also described parasites reaching the brain, bones, nerves and colon. Those claims are examined on sibling pages (see Parasites in the Brain). This page tests only the numbers: how many people carry parasites, where, and how the burden is measured.

How Parasite Numbers Are Counted

Before comparing figures, it helps to know that "how common" can mean several different things. Published numbers are not interchangeable.

Infection, disease and exposure

• Prevalence is the share of people who carry an infection at a given time. A survey that examines stool for worm eggs measures current infection.
• Seroprevalence is the share of people whose blood contains antibodies to a parasite. Antibodies show that the immune system met the parasite at some point. They usually cannot tell a past infection from a current one, so antibody surveys measure exposure, not active disease.
• Infection is not the same as illness. World Health Organization notes that people with light worm infections usually do not suffer from them; symptoms depend on how many worms a person carries.

Years of healthy life lost

Disease-burden studies use the disability-adjusted life year (DALY). One DALY is one year of healthy life lost, either through early death or through living with illness or disability. The "years lived with disability" (YLD) part counts only the illness side. The Global Burden of Disease (GBD) study, a large international modelling project, publishes these figures for most diseases and countries.

Why counts differ

Estimates for parasites are built from surveys that vary in age group, test method and year, then filled in with statistical models where data are missing. Different tests find very different numbers: microscopy misses light infections that DNA tests (polymerase chain reaction (PCR), the polymerase chain reaction) can detect, and some parasites, such as Strongyloides, need special tests altogether. Many people carry more than one parasite at once, so figures for separate parasites cannot simply be added together.

Intestinal Worms Worldwide

The single largest group is the soil-transmitted helminths — intestinal worms whose eggs or larvae pass out in human faeces and contaminate soil where sanitation is poor. The main species are the roundworm (Ascaris lumbricoides), the whipworm (Trichuris trichiura) and the hookworms (Necator americanus and Ancylostoma duodenale).

What World Health Organization reports

• World Health Organization's fact sheet on soil-transmitted helminth infections states that they are among the most common infections worldwide, with an estimated 1.5 billion infected people, or 24% of the world's population.
• The highest prevalence is reported from sub-Saharan Africa, China, South America and Asia, in communities with poor access to clean water, sanitation and hygiene.
• World Health Organization counts over 260 million preschool-age children, 654 million school-age children, 108 million adolescent girls and 138.8 million pregnant and breastfeeding women living in areas where these worms are intensively transmitted.
• Separately, World Health Organization estimates that over 600 million people are infected with the threadworm Strongyloides stercoralis. World Health Organization notes that this worm needs different diagnostic tests from the others and is frequently not identified.

The species-by-species estimate

A global mapping study using surveys from 6,091 locations in 118 countries estimated that in 2010 about 819.0 million people carried Ascaris roundworm, 464.6 million carried whipworm and 438.9 million carried hookworm (Pullan and colleagues, 2014). Of the 4.98 million years lived with disability attributed to these worms, 65% came from hookworm, which feeds on blood. About two-thirds of the infections (67%) were in Asia.

The trend

World Health Organization reports that over 500 million children were treated with deworming medicines in 2021, about 62% of the children at risk, and that between 2010 and 2019 the healthy years lost each year to these worms fell by more than half as preventive treatment was scaled up. World Health Organization's control strategy, called preventive chemotherapy, is periodic treatment of at-risk groups in endemic areas without testing each person first.

Schistosomiasis and Malaria

Schistosomiasis

Schistosomiasis is caused by blood flukes whose larvae, released by freshwater snails, burrow through the skin of people in contact with infested water. World Health Organization's fact sheet reports that:

• at least 253.7 million people required preventive treatment for schistosomiasis in 2024, and more than 100.5 million were reported treated;
• transmission has been reported from 79 countries, and at least 93.9% of the people requiring treatment live in Africa;
• deaths are currently estimated at 14,353 a year, a figure World Health Organization describes as likely underestimated because of hidden complications such as liver and kidney failure and bladder cancer.

The link between one species, Schistosoma haematobium, and bladder cancer is covered on the sibling page Schistosoma and Bladder Cancer.

Malaria

Malaria is caused by Plasmodium parasites carried by Anopheles mosquitoes. World Health Organization's malaria fact sheet reports an estimated 282 million malaria cases and 610,000 malaria deaths in 2024, in 80 countries. The World Health Organization African Region carried about 95% of both cases and deaths, and children under 5 accounted for about three-quarters of the malaria deaths in that region.

Malaria counts are counts of illness episodes in a year, not of people carrying parasites at one moment, so they measure something different from the worm figures above.

Death and Disability: The Global Burden Figures

The latest Global Burden of Disease round

An analysis of GBD 2021 data covering 204 countries reported that neglected tropical diseases and malaria together caused 71.63 million DALYs in 2021, down 18.06% from 87.42 million in 1990 (Zheng and colleagues, 2026). Prevalence fell by 58.05% over the same period. Western sub-Saharan Africa had the highest incidence, and children under five had the highest rates. Note that the GBD "neglected tropical diseases" group also includes infections that are not parasites, such as dengue, rabies and leprosy.

Dividing 71.63 million DALYs by a world population of roughly 7.9 billion gives a worldwide average of about 0.009 healthy years, or roughly three days, lost per person per year for this whole group. That is this page's own arithmetic, not a figure from the paper; the burden is concentrated in a small number of high-burden regions and is far lower elsewhere.

How reliable are the models?

A study comparing GBD 2021 estimates with China's reported surveillance data for six neglected tropical diseases from 2004 to 2020 found large gaps (Yang and colleagues, 2025). The GBD estimate was 1.5 times the reported figure for schistosomiasis, 11 times for echinococcosis (hydatid disease) and 280 times for visceral leishmaniasis. The authors concluded that global estimates alone may not capture local patterns. Model-based numbers can therefore be higher or lower than what is found on the ground.

Parasites from food

World Health Organization's Foodborne Disease Burden Epidemiology Reference Group estimated that 11 foodborne parasitic diseases caused 48.4 million cases, 59,724 deaths and 8.78 million DALYs in 2010 (Torgerson and colleagues, 2015). Human cysticercosis (the pork-tapeworm larval disease) caused the largest DALY burden, followed by foodborne flukes and toxoplasmosis. An updated World Health Organization synthesis covering 2000–2021 reported 277 million illnesses from 14 potentially foodborne invasive parasites, about 171 million of them attributed to food, and 4.89 million foodborne DALYs, led by the pork tapeworm Taenia solium and the Chinese liver fluke Clonorchis sinensis (Robertson and colleagues, 2026). That update found the burden greatest in the Americas, mainly from Chagas disease, and found burdens falling globally except in the Western Pacific region.

The 2004 map in the presentation

This page could not identify the exact map shown or confirm its "more than half a year per person" figure. World Health Organization's burden estimates from that era have since been replaced by several newer GBD rounds, and the newer rounds report falling, not rising, burdens for this group of diseases overall.

Parasites in the United States

The speaker's point that parasites are found in wealthy countries is well documented. The U.S. Centers for Disease Control and Prevention and national surveys report the following figures for the United States.

U.S. Centers for Disease Control and Prevention figures

• Toxoplasma gondii: the U.S. Centers for Disease Control and Prevention states that over 40 million people in the United States are infected with this single-celled parasite. Most people with healthy immune systems have no symptoms, and the infection can last a lifetime.
• Trichomonas vaginalis: the U.S. Centers for Disease Control and Prevention estimates more than two million trichomoniasis infections in 2018, describing it as the most common curable sexually transmitted infection; about 70% of infected people have no symptoms.
• Giardia: the U.S. Centers for Disease Control and Prevention states that more than 1 million people get sick from Giardia every year.
• Chagas disease (Trypanosoma cruzi): the U.S. Centers for Disease Control and Prevention estimates about 8 million people infected worldwide, including an estimated 280,000 in the United States, often without knowing it.
• Pinworm: the U.S. Centers for Disease Control and Prevention describes pinworm as the most common worm infection in the United States, most often in school-age and preschool children and their households.
• Malaria: about 2,000 cases a year are reported in the United States, almost all acquired during travel, with on average nearly 7 deaths a year from 2007 to 2022.

National blood surveys

The National Health and Nutrition Examination Survey (NHANES) tests blood from a sample designed to represent the United States population.

• In 13,507 people aged 6 and older tested in 2011–2014, 11.14% had antibodies to Toxoplasma (age-adjusted 10.42%), and 7.50% of women aged 15–44 (Jones and colleagues, 2018). Risk was higher with older age, in men, below the poverty line, with less education and in people born outside the United States.
• In the same survey years, the age-standardised seroprevalence of antibodies to Toxocara, the dog and cat roundworm, was 5.0%, lower than the 13.9% reported in 1988–1994 (Liu and colleagues, 2018). Risk factors included older age, poverty, crowding, less than college education and birth outside the United States.

Both are antibody surveys, so they measure lifetime exposure, not the number of people with an active infection today.

"Neglected infections of poverty"

A 2008 review grouped toxocariasis, strongyloidiasis, ascariasis, cysticercosis, trichomoniasis, Chagas disease, leishmaniasis and congenital toxoplasmosis among the "neglected infections of poverty" in the United States (Hotez, 2008). It reported that they occur mainly in poor communities — the Mississippi Delta and the wider American South, disadvantaged urban areas, the US–Mexico border region, some immigrant populations and Appalachia — and estimated that tens of thousands, and for some infections hundreds of thousands, of Americans carry them. The review called for active surveillance because accurate population counts did not exist.

Hookworm and the American South

Hookworm was once common in the southern United States and declined with improved sewage disposal and eradication programmes. Recent studies have asked whether it is still there, with mixed results that show how much the answer depends on the test used.

• Alabama, 2017. In Lowndes County, an area with open-sewage systems, 19 of 55 stool samples (34.5%) tested positive for Necator americanus hookworm DNA by quantitative polymerase chain reaction, four (7.3%) for Strongyloides and one for Entamoeba histolytica (McKenna and colleagues, 2017). The amount of hookworm DNA found was very low, and 42.4% of 24 households reported exposure to raw sewage inside the home.
• Alabama, 2023. A larger study in the Black Belt region of Alabama enrolled 777 children and examined stool from 704 by microscopy, with polymerase chain reaction on a subset. Stool testing for soil-transmitted helminths was negative, although 5% of dried blood spots had antibodies to Toxocara and 12% of children lived in homes that discharge untreated wastewater (Poole and colleagues, 2023).
• Mississippi, 2023. Stool from 277 children in Rankin County was tested by microscopy, culture and polymerase chain reaction; no soil-transmitted helminths were found (Bradbury and colleagues, 2023).
• Soil, 2024. DNA testing of 499 soil samples from parks and homes in five low-income communities in Alabama, Louisiana, Mississippi, South Carolina and Texas found Blastocystis in 19.03%, the cat roundworm Toxocara cati in 6.01%, the dog roundworm Toxocara canis in 3.61%, Strongyloides in 2.00% and smaller shares of other parasites (Crudo Blackburn and colleagues, 2024). Overall contamination ranged from 46.88% of samples in western Mississippi to 6.93% in south Texas. Soil DNA shows that parasites are present in the environment, not that people living there are infected.

Together these studies show that parasites still circulate in some poor southern communities, while large surveys of children have not found widespread intestinal worm infection.

Parasites in Europe and the Blastocystis Question

The speaker named Switzerland and Germany. No country-specific prevalence study for those two countries was examined for this page, but European pooled data exist.

• A review and meta-analysis of eight cross-sectional studies published 2015–2021, covering 3,376 European children, found an overall prevalence of 5.9% for any intestinal parasitic infection (Kantzanou and colleagues, 2021). Blastocystis was the most commonly detected organism, at 10.7%. Studies that looked for one parasite reported figures ranging from 1.3% for Cryptosporidium to 68.3% for Dientamoeba fragilis. The authors described the overall rates as relatively low and noted that the literature is scarce.

Is everything found in a stool test a disease?

Some of the most commonly detected organisms are of uncertain harm. A Dutch case-control study tested 1,374 people with gastroenteritis and 1,026 people without it (de Boer and colleagues, 2020). Dientamoeba fragilis and Blastocystis were found less often in the sick group (both 25.8%) than in the healthy controls (37.6% and 40.0%), and their presence was not linked to any gut symptom. The authors suggested these protozoa may be a feature of a healthy gut microbiome.

This matters for prevalence figures: counts that include Blastocystis or Dientamoeba can look high while saying little about disease.

Food- and Water-Borne Protozoa

Protozoa are single-celled parasites. Several cause outbreaks in wealthy countries through contaminated food or water.

Cyclospora

• A review reported that at least 54 countries have documented Cyclospora cayetanensis infections, 13 of them with recorded outbreaks, and gave an overall human prevalence worldwide of 3.55% (Li and colleagues, 2020). Infections are markedly seasonal.
• The U.S. Centers for Disease Control and Prevention describes cyclosporiasis as less common in the United States but notes outbreaks linked to various types of fresh produce.
• A second review concluded that few epidemiological data exist for Cyclospora in both poor and developed countries and that its effect on human health is likely underestimated (Giangaspero and Gasser, 2019).

Cryptosporidium and Giardia

The U.S. Centers for Disease Control and Prevention describes cryptosporidiosis as a disease of watery diarrhoea that some infected people have without any symptoms, and states that more than 1 million people in the United States get sick from Giardia each year. In the European children's meta-analysis, studies looking for Cryptosporidium found it in 1.3% of children (Kantzanou and colleagues, 2021).

Are Parasites Missed in Wealthy Countries?

The speaker's point that parasites are under-diagnosed in developed countries has some support in the published literature, although the size of the gap is not measured.

• A review in a gastroenterology journal noted that the routine three-sample stool test for ova and parasites is almost always negative in the United States, which has contributed to a perception that parasitic diseases barely exist there unless a patient has travelled (Mohapatra and colleagues, 2018). The authors wrote that immigrants, tourists and students with parasitic symptoms are often misdiagnosed with irritable bowel syndrome or inflammatory bowel disease, and that some parasitic diseases are endemic in the United States and other developed nations.
• World Health Organization notes that Strongyloides needs different diagnostic methods from other intestinal worms and for that reason is frequently not identified.
• The U.S. Centers for Disease Control and Prevention notes that most people infected with Toxoplasma, Toxocara or Trichomonas have no symptoms, so many infections are never tested for.
• The 2017 Alabama study found hookworm only by sensitive DNA testing, at very low DNA levels (McKenna and colleagues, 2017).

How stool tests work and where they fall short is covered on the sibling page Stool Tests for Parasites and Their Limits.

How the Claim Compares With the Research

"Over 3 million people harbour parasites"

• Contradicted by the published counts, in the direction of being far too low. World Health Organization's figure for soil-transmitted helminths alone is about 1.5 billion people, roughly 500 times 3 million. World Health Organization adds over 600 million people with Strongyloides, at least 253.7 million needing treatment for schistosomiasis and 282 million malaria cases in 2024. Because many people carry more than one parasite, these figures cannot be added, but each on its own is far above 3 million.
• The transcript is machine-generated, so the figure may be a slip for "billion". Either way, the speaker's added remark that the true number is likely greater than stated is consistent with the published estimates.

Parasites are everywhere, including wealthy countries

• Supported. U.S. Centers for Disease Control and Prevention and national survey data show tens of millions of Americans with antibodies to Toxoplasma, millions of trichomoniasis infections, more than a million Giardia illnesses a year, an estimated 280,000 people with Chagas disease and pinworm as a common childhood infection. European children's surveys find intestinal parasites in about 6%.
• Supported only in part. The burden is very uneven. Intestinal worms, schistosomiasis and malaria are concentrated in tropical and subtropical regions with poor sanitation; World Health Organization places about 95% of malaria cases in Africa and at least 93.9% of people needing schistosomiasis treatment in Africa. Recent large surveys of children in Alabama and Mississippi found no intestinal worm infections. Many of the parasites common in wealthy countries (Toxoplasma, Blastocystis, Dientamoeba) usually cause no symptoms, and some may be harmless.

Under-diagnosis in developed countries

• Supported in part. Reviews and World Health Organization describe parasites that are easily missed by routine tests (Strongyloides, light hookworm infections) and misdiagnosis as bowel disorders. No study found for this page measures what share of infections in developed countries goes undiagnosed.

The 2004 World Health Organization map and "more than half a year per person"

• Could not be confirmed. The map and its figure could not be traced. The most recent GBD analysis reports 71.63 million DALYs for neglected tropical diseases and malaria together in 2021, which averages to a few days per person per year worldwide.
• Contradicted on the trend. The speaker suggested the burden may be greater in 2026 than in 2004. The GBD 2021 analysis reports that DALYs from this group fell by 18% from 1990 to 2021, World Health Organization reports that healthy years lost to soil-transmitted helminths fell by more than half from 2010 to 2019, and the 2026 World Health Organization foodborne-parasite update reports falling burdens globally except in the Western Pacific. Some individual infections, such as clonorchiasis in the Western Pacific, are rising.

What Is Not Known

• A single total. No source found for this page gives one verified number for all people carrying any parasite. Counts exist parasite by parasite and overlap.
• Strongyloides. The 600-million figure rests on limited testing, because the worm is hard to detect.
• Wealthy countries. The United States and most European countries do not routinely survey the general population for intestinal parasites. Hotez (2008) called for active surveillance because accurate counts for the "neglected infections of poverty" did not exist.
• Harmless or harmful? Whether Blastocystis and Dientamoeba fragilis cause disease, and in whom, is still debated, which changes how "common" parasitic disease looks.
• Exposure versus infection. Antibody surveys for Toxoplasma and Toxocara show past exposure; how many of those people still carry living parasites is not known.
• Model accuracy. The comparison of GBD estimates with China's surveillance data shows that modelled figures can differ from reported figures several-fold, in either direction, for some diseases.

Decisions about testing for or treating any parasite belong with a clinician.

Connections

• Cancer and Parasites
• Parasites in the Brain
• Stool Tests for Parasites and Their Limits
• Food Sources of Parasites
• Do Parasites Steal Your Nutrients?
• Parasites
• Hookworm
• Ascaris
• Strongyloides
• Pinworm
• Toxoplasma
• Toxocara
• Cyclospora
• Cryptosporidium
• Blastocystis
• Malaria
• Schistosoma

Key Research Papers

1. Pullan RL, Smith JL, Jasrasaria R, Brooker SJ. Global numbers of infection and disease burden of soil transmitted helminth infections in 2010. Parasit Vectors. 2014;7:37. PubMed PMID: 24447578
2. Zheng JX, Liu Y, Guan SY, Guo ZY, Duan L, Lv S, Zhang SX, Li SZ, Zhou XN, Feng XY. Global, regional, and national burden of neglected tropical diseases and malaria in the general population, 1990-2021: Systematic analysis of the global burden of disease study 2021. J Adv Res. 2026;79:769-781. PubMed PMID: 40194698
3. Yang GJ, Ouyang HQ, Zhao ZY, Li WH, Fall IS, Djirmay AG, Zhou XN. Discrepancies in neglected tropical diseases burden estimates in China: comparative study of real-world data and Global Burden of Disease 2021 data (2004-2020). BMJ. 2025;388:e080969. PubMed PMID: 39965820
4. Torgerson PR, Devleesschauwer B, Praet N, Speybroeck N, Willingham AL, Kasuga F, et al. World Health Organization Estimates of the Global and Regional Disease Burden of 11 Foodborne Parasitic Diseases, 2010: A Data Synthesis. PLoS Med. 2015;12(12):e1001920. PubMed PMID: 26633705
5. Robertson LJ, Minato Y, Devleesschauwer B, Di Bari C, Vaes L, Keddy KH, et al.; WHO Foodborne Disease Burden Epidemiology Reference Group for 2021–25. WHO estimates of the global, regional, and national foodborne burdens of 14 invasive parasitic diseases, 2000-21: an updated data synthesis. Lancet Glob Health. 2026;14(8):103982. PubMed PMID: 42302806
6. Hotez PJ. Neglected infections of poverty in the United States of America. PLoS Negl Trop Dis. 2008;2(6):e256. PubMed PMID: 18575621
7. Jones JL, Kruszon-Moran D, Elder S, Rivera HN, Press C, Montoya JG, McQuillan GM. Toxoplasma gondii Infection in the United States, 2011-2014. Am J Trop Med Hyg. 2018;98(2):551-557. PubMed PMID: 29260660
8. Liu EW, Chastain HM, Shin SH, Wiegand RE, Kruszon-Moran D, Handali S, Jones JL. Seroprevalence of Antibodies to Toxocara Species in the United States and Associated Risk Factors, 2011-2014. Clin Infect Dis. 2018;66(2):206-212. PubMed PMID: 29020386
9. McKenna ML, McAtee S, Bryan PE, Jeun R, Ward T, Kraus J, Bottazzi ME, Hotez PJ, Flowers CC, Mejia R. Human Intestinal Parasite Burden and Poor Sanitation in Rural Alabama. Am J Trop Med Hyg. 2017;97(5):1623-1628. PubMed PMID: 29016326
10. Poole C, Barker T, Bradbury R, Capone D, Chatham AH, Handali S, Rodriguez E, Qvarnstrom Y, Brown J. Cross-Sectional Study of Soil-Transmitted Helminthiases in Black Belt Region of Alabama, USA. Emerg Infect Dis. 2023;29(12):2461-2470. PubMed PMID: 37987581
11. Bradbury RS, Martin L, Malloch L, Martin M, Williams JM, Patterson K, et al. Surveillance for Soil-Transmitted Helminths in High-Risk County, Mississippi, USA. Emerg Infect Dis. 2023;29(12):2533-2537. PubMed PMID: 37987591
12. Crudo Blackburn C, Yan SM, McCormick D, Herrera LN, Iordanov RB, Bailey MD, Bottazzi ME, Hotez PJ, Mejia R. Parasitic Contamination of Soil in the Southern United States. Am J Trop Med Hyg. 2024;111(3):506-514. PubMed PMID: 39043177
13. Kantzanou M, Karalexi MA, Vrioni G, Tsakris A. Prevalence of Intestinal Parasitic Infections among Children in Europe over the Last Five Years. Trop Med Infect Dis. 2021;6(3):160. PubMed PMID: 34564544
14. de Boer MD, Schuurs TA, Vermeer M, Ruijs GJHM, van der Zanden AGM, Weel JF, Bruijnesteijn van Coppenraet LES. Distribution and relevance of Dientamoeba fragilis and Blastocystis species in gastroenteritis: results from a case-control study. Eur J Clin Microbiol Infect Dis. 2020;39(1):197-203. PubMed PMID: 31659566
15. Li J, Wang R, Chen Y, Xiao L, Zhang L. Cyclospora cayetanensis infection in humans: biological characteristics, clinical features, epidemiology, detection method and treatment. Parasitology. 2020;147(2):160-170. PubMed PMID: 31699163
16. Giangaspero A, Gasser RB. Human cyclosporiasis. Lancet Infect Dis. 2019;19(7):e226-e236. PubMed PMID: 30885589
17. Mohapatra S, Singh DP, Alcid D, Pitchumoni CS. Beyond O&P Times Three. Am J Gastroenterol. 2018;113(6):805-818. PubMed PMID: 29867172

PubMed Topic Searches

1. PubMed: Soil-transmitted helminth global prevalence
2. PubMed: Neglected tropical diseases and the Global Burden of Disease
3. PubMed: Neglected parasitic infections in the United States
4. PubMed: Intestinal parasite prevalence in Europe

Other Sources

1. World Health Organization. Soil-transmitted helminth infections, fact sheet. who.int
2. World Health Organization. Schistosomiasis, fact sheet. who.int
3. World Health Organization. Malaria, fact sheet. who.int
4. Centers for Disease Control and Prevention. About Toxoplasmosis. cdc.gov
5. Centers for Disease Control and Prevention. About Toxocariasis. cdc.gov
6. Centers for Disease Control and Prevention. About Trichomoniasis. cdc.gov
7. Centers for Disease Control and Prevention. About Giardia Infection. cdc.gov
8. Centers for Disease Control and Prevention. About Chagas Disease. cdc.gov
9. Centers for Disease Control and Prevention. About Pinworm Infection. cdc.gov
10. Centers for Disease Control and Prevention. About Cyclosporiasis. cdc.gov
11. Centers for Disease Control and Prevention. About Crypto Infections. cdc.gov
12. Centers for Disease Control and Prevention. Data and Statistics on Malaria in the United States. cdc.gov

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