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1. Ascaris, Trichuris, Enterobius, Ancylostoma, Strongyloides and Trichinella(Nematoda), and the diseases that these roundworms cause in humansPaul R. EarlFacultad de Ciencias BiológicasUniversidad Autónoma de Nuevo LeónSan Nicolás, NL, México

2. Parasitic nematodes inhabit many thousands of plant and animal hosts. Some of the most common parasitic roundworms in humans are: a) Ascaris lumbricoides, the large intestinal roundworm that causes ascariasis, b) Trichuris trichiura, the whipworm that causes trichuriasis, c) Enterobius vermicularis, the pinworm of enterobiasis, d) Necatoramericanus and Ancylostoma duodenale, 2 types of hookworms that cause ancylostomiasis, e) Strongyloides stercoralis responsible for strongyloidiasis and f) Trichinella spiralis which causes trichinosis that perhaps ought to be called trichinellosis.

3. A parasite is an organism that exists by depending on another organism. Parasites that infect humans are much more widespread and prevalent than many people realize. Nematode diseases are important health problems for rich and poor throughout the world. As with other parasitic diseases, some roundworm infections are more common in warm climates than in cooler, temperate areas. Many roundworm parasitic diseases result from human carelessness and lack of appropriate personal hygiene and sanitation measures. Thus, the best solution to the problem rests in preventing these infections rather than in curing them.

4. Roundworms or nematodes are a group of invertebrates (animals having no backbone) with long, round bodies. They range in size from those visible to the naked eye to those several hundredths-of-a-mm long and visible only under a microscope. Most roundworms or their eggs are found in the soil and can be picked up on the hands and transferred to the mouth or can enter through the skin. With the exception of the roundworm that causes trichinellosis found in muscles, mature roundworms invade the human intestines and cause a variety of health problems.

5. Ascaris lumbricoides.The incidence is over 1500 million infections annually. Of these cases, about 210 million are symptomatic. In some rural settings with poor sanitation, perhaps half the children of 2-12 years have ascariasis. Then many of them will also have trichuriasis and various of other chronic illnesses.

6. 40cm

7. A mass or bolus of Ascaris lumbricoides.

8. Trichuris trichuriura. These whipworms cause 800 million infections per year worldwide. Trichuriasis occurs in the southern United States and Latin America.Female whipworm, Trichuris trichiura.

9. Enterobius vermicularis. Enterobius vermicularis male. Enterobius vermicularis female. Enterobius egg in feces.

10. Necatur americanus and Ancyclostoma duodenale. The human hookworms include 2 nematode (roundworm) species, Ancylostoma duodenale and Necator americanus. Adult females measure 10-13 mm for A. duodenale and 9-11 mm for N. americanus. adult males: 8 to 11 mm (A. duodenale), 7 to 9 mm (N. americanus).

11. Ancyclostoma duodenale.

12. The second most common human helminthic infection after ascariasis is ancylostomiasis. Worldwide distribution, mostly in areas with moist, warm climates. Both N. americanus and A. duodenale are found in Africa, Asia and the Americas.  Necator americanus predominates in the Americas and Australia, while only A.duodenale is found in the Middle East, North Africa and southern Europe.

13. Strongyloides stercoralis has both freeliving and parasitic life cycles. In the parasitic life cycle, female worms are found in the superficial tissues of the human small intestine. There are no parasitic males. The female worms produce larvas parthenogenically (without fertilization) and the larvas are passed in the host's feces. The presence of nematode larvas in a fecal sample is characteristic of strongylodiasis. Once passed in the feces, some of the larvas develop into freeliving larvas, while others develop into parasitic larvas. The freeliving larvas will complete their development in the soil and mature into freeliving males and females.

15. Two types of cycles exist in Strongyloides.1/ Freeliving cycle: The rhabditiform larvas passed in the stool can either molt twice and become infective filariform larvae (direct development) or molt 4 times and become freeliving adult males and females that mate and produce eggs which hatch as rhabditiform larvas that can either develop into a new generation of freeliving adults, or into infective filariform larvas. The filariform larvas penetrate the human host skin to initiate the parasitic cycle.

16. Trichinella spiralis Muscle can be squeezed between 2 plates of glass to reveal microscopic larvas.

17. Trichinosis is probably best known as a parasite that humans contract from eating raw or undercooked pork. Through an aggressive program of meat inspection, the incidence of trichinosis in pigs in the US has been lowered to less than 1%, so it is unlikely that those pork products will contain Trichinella larvas. Most recent outbreaks of trichinosis in the US have been traced to pork products from pigs that have not been inspected and that have been slaughtered privately. As T. spiralis is not host specific, hunters should be careful when preparing meat from their kills, e. g., infections have been traced to contaminated bear meat.

18. Endnote. We have introduced you to soil transmitted nematodes and to Trichinella spiralis transmitted in undercooked meat. The much greater problem is the sanitation of food, water and waste disposal. The lack of safe water and drainage is allied to poverty and high birth rates. No water delivered to the home and dirt floors are common aspects of poverty. How many houses have latrines? The migrant can live anywhere as long as he can get a job. Shantytown barrios have sprung up over much of the world and deteriorate their environments.

19. Parasitic diseases are part of this, although generally they cannot be vaccine prevented. Massive population treatments with one-time 400 mg mebendazole or the like may be the road to take. These populations are infected yet not seeking treatment. Worms have never been seen damaging enough to eradicate. Perhaps the determination needed to eliminate roundworms is at the end of the rainbow. Generally, people with parasitoses are poor, and many are rural. Is industry the real solution? It is the only solution ! Finally, world economics is such that the pills like the vaccines MUST be given by generous donors like Merck.