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How common are parasites in the world?

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More then 60% of people on planet Earth carry at least one parasite   by #56153   18 year


How common are Internal parasites in the world?

How common are internal parasitic animals?

It is estimated that more then 60% of people on planet Earth carry at least one parasite.  Many people carry several different species.

Intestinal parasites cause significant morbidity and mortality. Diseases caused by Ascaris lumbricoides, Enterobius vermicularis, Giardia lamblia, Ancylostoma duodenale, Necator americanus,Entamoeba histolytica, Plasmodium falciparum, Fasciola hepatica, Entamoeba dispar, Entamoeba coli, Entamoeba hartmanni, I. bütschlii, D. fragilis, and Giardia intestinalis occur in Europe and in the United States.


How common are parasites in North America?

Common Parasites in North America and their Health Implications.
Reprinted from:

The most common parasites identified from North American patients at the Parasitology Center, Inc. (PCI), Tempe, Arizona are listed below in order of their prevalence from high to low:

         Protozoa (microscopic single-celled organisms)
         Blastocystis hominis
         Endolimax nana
         Cryptosporidiuin parvum
         Entamoeba histolytica
         Entamoeba coli
         Entamoeba hartmanni
         Giardia lamblia
         Chilomastix mesnili
         Cyclospora cayetanensis
         Helminths (macroscopic multicellular worms)
         Ascaris lumbricoides (human roundworm)
         Strongyloides stercoralis (threadworm)
         Ancylostoma duodenale/Necator americanus (hookworms)
         Enterobius vermicularis (pinworm)
         Trichuris trichiura (whipworm)

In the USA, one-third of about 6,000 fecal specimens tested at PCI were positive for 19 species of intestinal parasites (Amin, 0. 2002.Seasonal Prevalence of Intestinal Parasites in the United States during 2000.,  American Journal of Tropical Medicine and Hygiene 66(6):799-803).

Between 80 and 100 percent of sexually active homosexual men worldwide are infected with one or more species of intestinal parasite. The epidemic of parasites in gay men preceded AIDS by a few years.

E. vermicularis, or pinworm, causes irritation and sleep disturbances. Diagnosis can be made using the "cellophane tape test." It is the most prevalent nematode in the United States and in Europe.

Giardia causes nausea, vomiting, malabsorption, diarrhea, and weight loss. Stool ova and parasite studies are diagnostic. Sewage treatment, proper hand washing, and consumption of bottled water can be preventive.

A. duodenale and N. americanus are hookworms that cause blood loss, anemia, pica, and wasting. Finding eggs in the feces is diagnostic. Preventive measures include wearing shoes and treating sewage.

E. histolytica can cause intestinal ulcerations, bloody diarrhea, weight loss, fever, gastrointestinal obstruction, and peritonitis. Amoebas can cause abscesses in the liver that may rupture into the pleural space, peritoneum, or pericardium. Stool and serological assays, biopsy, barium studies, and liver imaging have diagnostic merit. Careful sanitation and use of peeled foods and bottled water are preventive. (Am Fam Physician 2004:69:1161-8. Copyright© 2004 American Academy of Family Physicians)

Giardia lamblia

G. lamblia is a pear-shaped, flagellated protozoan (Figure 2) that causes a wide variety of gastrointestinal complaints. Giardia is arguably the most common parasite infection of humans worldwide, and the second most common in the United States after pinworm.8,9 Between 1992 and 1997, the Centers for Disease Control and Prevention (CDC) estimated that more than 2.5 million cases of giardiasis occur annually.10

Estimates of current numbers of human helminth (worm) infections

Source: Journal of Parasitology 85:379-403 Dr. D.W.T. Crompton (Crompton, D.W.T. [1999] How much human helminthiasis is there in the world?)

The species shown in red are considered to be the "commonest helminths or
those judged to have [the] most general public health significance."

Helminth species
Ancylostoma duodenale and Necator americanus
Worldwide; developing countries
Ascaris lumbricoides
Worldwide; developing countries
Brugia malayi and Brugia timori
E. Indonesia islands; Philippines; S.E. Asia; Southern China; India.
Clonorchis sinensis
China; Korea; Taiwan; Vietnam
Diphyllobothrium latum
Worldwide where certain raw fish is eaten.
Dracnunculus medinensis
Sub-Sahara Africa; Yemen
Echinococcus granulosus and Echinococcus multilocularis
Echinostoma spp.
Philippines; Thailand
Fasciola hepatica and Fasciola gigantica
China; Egypt; Europe; Iran; South America
Fasciolopsis buski
Bangladesh; Cambodia; China; India; Indonesia; Laos; Thailand; Vietnam.
Heterophyes heterophyes (and related species)
Egypt; Iran; Korea
Hymenolepis nana
Americas; Australia; developing countries
Loa loa
West and central Sub-Saharan Africa
Metagonimus yokogawai (and related species)
Korea; S.E. Asia.
Onchocerca volvulus
Central and South America; Sub-Saharan Africa; Yemen
Opisthorchis viverrini and Opisthorchis felineus
Kazakhastan; Laos; Thailand; Ukraine
Paragonimus westermani (and related species)
China; Laos; Korea; Ecuador; Peru
Schistosoma haematobium
Africa; E. Mediterranean region
Schistosoma intercalatum
Sub-Saharan Africa
Schistosoma japonicum
China; Western Pacific region
Schistosoma mansoni
Africa; Caribbean; E. Mediterranean region
Schistosoma mekongi
Cambodia; Laos
Strongyloides stercoralis
Worldwide (warmer countries)
Taenia saginata
Worldwide (related to beef consumption)
Taenia solium
Worldwide (related to raising pigs for pork)
Trichuris trichiura
Worldwide; developing countries
Wuchereria bancrofti
Asia; Central and South America; Sub-Saharan Africa; West Pacific countries

Ascaris lumbricoides

"Ascaris Lumbricoides has a world-wide distribution and is most prevalent in tropical areas. 25% of the world population harbors the parasite. "

Ascaris lumbricoides is one of the largest and most common parasites found in humans.The adult females of this species can measure up to 18 inches long (males are generally shorter), and it is estimated that 25% of the world's population is infected with this nematode.The adult worms live in the small intestine and eggs are passed in the feces.A single female can produce up to 200,000 eggs each day!About two weeks after passage in the feces the eggs contain an infective larval or juvenile stage, and humans are infected when they ingest such infective eggs."

Fasciola hepatica is found in parts of the United States (view distribution), as well as in Great Britian, Ireland, Europe, the Middle East, the Far East, Africa, and Australia.

In a fecal exam, parasitologists are looking for the microscopic eggs of the worms. Eggs may not always be present in the stool, even though you might have worms. This is why regular deworming is advisable, even though evidence of worms may not be present.

E. vermicularis (pinworm)

"It is estimated that pinworms infect more than 400,000,000 people throughout the world (10% of humans), and in many areas of the world (e.g., North America and Europe) it is the most common nematode parasite of humans.On a world-wide basis, however, Ascaris lumbricoides ranks #1 infecting more than 1,000,000,000 people (25% of humans).

E. vermicularis, commonly referred to as the pinworm or seatworm, is a nematode, or roundworm, with the largest geographic range of any helminth.1 It is the most prevalent nematode in the United States. Humans are the only known host, and about 209 million persons worldwide are infected. More than 30 percent of children worldwide are infected.2

1. Neva FA, Brown HW. Basic clinical parasitology. 6th ed. Norwalk, Conn.: Appleton & Lange, 1994.

2. Goldmann DA, Wilson cm. Pinworm infestations. In: Hoekelman RA. Primary pediatric care. 3d ed. St. Louis: Mosby, 1997:1519.


Entamoeba histolytica:

Amoebiasis - death and illness due to dysentery and liver abcess. Worldwide distribution. Estimated 40 million develop intestinal disease or liver abcess annually; 40,000 die from amoebiasis annually. Human is definitive host.

Amebiasis is caused by E. histolytica, a protozoan that is 10 to 60 µm in length and moves through the extension of finger-like pseudopods.1 Spreading occurs via the fecal-oral route, usually by poor hygiene during food preparation or by the use of "night soil" (crop fertilization with human waste), as well as by oral-anal sexual practices. Spreading is frequent in persons who have a deficient im-mune system. Crowding and poor sanitation contribute to its prevalence in Asia, Africa, and Latin America. Approximately 10 percent of the world's population is infected, yet 90 percent of infected persons are asymptomatic.17 Of the roughly 50 million symptomatic cases occurring each year, up to 100,000 are fatal.18 The stable reservoir of infective cases complicates eradication. After malaria, it is likely that E. histolytica is the world's second leading protozoan cause of death.19

The Bloodstream:

Plasmodium falciparum: (Malaria)

(Also P.vivax, P.malariae, P.ovale - cause less severe forms of malaria). Malaria - estimated 40% of world's population at risk; 10% severe risk. Major killer of children in tropical Africa. Tropics and subtropics - Africa, Asia and South America. Human is definitive host. Transmitted by mosquitoes - Anopheles. Lifecycle:

Table Showing Malaria Incidence,2000




Pf Cases




































































Note : ** : All Infromation relates to 1998; * : Java & Bali only ; Imported cases only

Updated as of 10 August 2001.

Surveillance report
Malaria incidence and mortality in Italy in 1999-2000

This document is also available in printer friendly pdf format

R. Romi, D. Boccolini, G. Majori

Laboratory of Parasitology, Istituto Superiore di Sanità, Rome, Italy

In 1999-2000, a total of 2060 malaria cases were reported by the ISS. Most of the patients took inappropriate treatments or did not have any prophylaxis. Ninety-three per cent became infected in African malarious countries, 4% in Asian countries, and 3% in Latin America. P. falciparum accounted for 84% of the cases, followed by P. vivax (8%), P. ovale (5%), and P. malariae (2%). Deaths corresponded to an annual case fatality rate of 0.3% in 1999 and 0.5% in 2000. In general, imported malaria cases reflect the number of Italian travellers who underestimate the infection risk in Asian and Latin American malarious countries and permanent residents of African origin who visit their relatives in their native countries.

Malaria is no longer endemic in Italy, but it is the disease most commonly imported into the country. Plasmodium falciparum malaria was eliminated from Italy in the 1950s, where as sporadic P. vivax cases occurred until 1962 in Sicily (1,2). In 1970, the World Health Organization (WHO) officially declared Italy malaria free. A surveillance system was established to prevent a possible return of malaria transmission and to monitor the epidemiology of imported cases. Until 1985, less than 100 cases of imported malaria were reported each year (3). Since then this figure has increased constantly, reaching a peak of 973 cases in 1998 (4). In the decade 1989-98, a total of 6871 malaria cases were officially confirmed; 6852 (99.7%) patients were infected while visiting malarious countries, and 19 (0.3%) were infected locally (4,5). Eighteen of the cases infected in Italy were classified as induced malaria (nine cases), airport malaria (two cases), and baggage malaria (seven cases) (3), and one case as introduced malaria; this was the first case transmitted by indigenous mosquitoes after malaria elimination in Italy (6). We report the epidemiological data on imported malaria in 1999 and 2000 and compare them with data from the previous decade. An evaluation of the incidence of malaria in Italian travellers to malarious countries is also reported.

Statistics on intercontinental travellers from Italy to countries where malaria is endemic were provided by the transport and aviation ministry. These data took into account only passengers leaving Italian airports by national or international airlines.


In the past two years, a total of 2060 cases of malaria were confirmed by the ISS: 1083 in 1999, and 977 in 2000 (figure 1). In both 1999 and 2000, only one case each of P. falciparum malaria was caused by blood transfusion.

Trypanosoma brucei rhodesiense and T. b. gambiense:

African sleeping sickness - East African form of disease (Rhodesian sleeping sickness) is acute, West African form (Gambian sleeping sickness) is more chronic. 25,000 cases reported per year, but 55 million estimated at risk. Restricted to tropical Africa, largely rural areas. Zoonotic infections, with both wild and domestic animals acting as reservoir hosts of disease. Transmitted by tsetse fly (Glossina):

Ancylostoma duodenale and Necator americanus

Two species of hookworm, A. duodenale and N. americanus, are found exclusively in humans. A. duodenale, or "Old World" hookworm, is found in Europe, Africa, China, Japan, India, and the Pacific islands. N. americanus, the "New World" hookworm, is found in the Americas and the Caribbean, and has recently been reported in Africa, Asia, and the Pacific.

Until the early 1900s, N. americanus infestation was endemic in the southern United States and was only controlled after the widespread use of modern plumbing and footwear. Even though the prevalence of these parasites has drastically decreased in the general population, the CDC reports that in the United States, hookworm infection is the second most common helminthic infection identified in stool studies.14


1. Neva FA, Brown HW. Basic clinical parasitology. 6th ed. Norwalk, Conn.: Appleton & Lange, 1994.

2. Goldmann DA, Wilson cm. Pinworm infestations. In: Hoekelman RA. Primary pediatric care. 3d ed. St. Louis: Mosby, 1997:1519.

3. MacPherson DW. Intestinal parasites in returned travelers. Med Clin North Am 1999;83:1053-75.

4. Saxena AK, Springer A, Tsokas J, Willital GH. Laparoscopic appendectomy in children with Enterobius vermicularis. Surg Laparosc Endosc Percutan Tech 2001;11:284-6.

5. Dickson R, Awasthi S, Demellweek C, Williamson P. Anthelmintic drugs for treating worms in children: effects on growth and cognitive performance. Cochrane Database Syst Rev 2003;(2): CD000371.

6. Parija SC, Sheeladevi C, Shivaprakash MR, Biswal N. Evaluation of lactophenol cotton blue stain for detection of eggs of Enterobius vermicularis in perianal surface samples. Trop Doct 2001;31(4):214-5.

7. Procop GW. Gastrointestinal infections. Infect Dis Clin North Am 2001;15:1073-108.

8. Katz DE, Taylor DN. Parasitic infections of the gastrointestinal tract. Gastroenterol Clin North Am 2001;30:795-815.

9. Leder K, Weller P. Giardiasis. In: Rose BD, ed. Infectious disease. Wellesley, Mass.: UpToDate, 2002.

10. Furness BW, Beach MJ, Roberts JM. Giardiasis surveillance-United States, 1992-1997. MMWR CDC Surveill Summ 2000;49(7):1-13.

11. DuPont HL, Backer HD. Infectious diarrhea from wilderness and foreign travel. In: Auerback PS, ed. Wilderness medicine: management of wilderness and environmental emergencies. 3d ed. St. Louis: Mosby, 1995:1028-59.

12. Glaser C, Lewis P, Wong S. Pet-, animal- and vector-borne infections. Pediatr Rev 2000;21:219-32.

13. Steiger U, Weber M. Ungewöhnliche ursache von erythema nodosum, pleuraerguss und reaktiver arthritis: giardia lamblia. [Unusual etiology of erythema nodosum, pleural effusion and reactive arthritis: Giardia lamblia.] Schweiz Rundsch Med Prax 2002;91:1091-2.

14. Centers for Disease Control and Prevention. Publication of CDC surveillance summaries. MMWR Morb Mortal Wkly Rep 1992;41(8):145-6.

15. Kitchen LW. Case studies in international medicine. Am Fam Physician 1999;59:3040-4.

16. Ali-Ahmad N, Bathija M, Abuhammour W. Index of suspicion. Case #2. Diagnosis: anemia from hookworm infestation. Pediatr Rev 2000;21:354-7.

17. Reed SL. Amebiasis and infection with free-living amebas. In: Harrison TR, Fauci AS, Braunwald E, et al., eds. Harrison's Principles of internal medicine. 15th ed. New York: McGraw-Hill, 2001:1199-202.

18. Walsh JA. Problems in recognition and diagnosis of amebiasis: estimation of the global magnitude of morbidity and mortality. Rev Infect Dis 1986;8:228-38.

19. Petri WA Jr, Singh U. Diagnosis and management of amebiasis. Clin Infect Dis 1999;29:1117-25.

20. Stanley SJ. Pathophysiology of amoebiasis. Trends Parasitol 2001;17:280-5.

21. Kimura K, Stoopen M, Reeder MM, Moncada R. Amebiasis: modern diagnostic imaging with pathological and clinical correlation. Semin Roentgenol 1997;32:250-75.

22. Huston CD, Petri WA. Amebiasis. In: Rakel R, ed. Conn's Current therapy 2001. Philadelphia: Saunders, 2001:64-5.

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