1. Ascaris, Trichuris, Enterobius, Ancylostoma, Strongyloides and Trichinella (Nematoda), and the diseases that these roundworms cause in humans Paul R. Earl Facultad de Ciencias Biológicas Universidad Autónoma de Nuevo León San Nicolás, NL, México

2. Parasitic nematodes inhabit many thousands of plant and animal hosts
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) Necator americanus 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.
Incidentally, no rightminded person will support N.americanus as a genus different from Ancyclostoma just because it has plates not teeth in its mouth.

3. A parasite is an organism that exists by depending on another organism
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.
These and other parasitic diseases are very well covered by the Division of Parasitic Diseases of the National Center for infectious Diseases of the US Centers for Disease Control and Prevention, by the Karolinska Institute, Stockholm, Sweden and by others on Internet.

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.
The life cycles of Ascaris lumbricoides and Ascaris suum (pic.GIF)

6. 40cm

7. A mass or bolus of Ascaris lumbricoides.

8. Trichuris trichuriura
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.
Life cycle (pic1.htm)
The unembryonated eggs are passed with the stool. In the soil, the eggs develop into a 2-cell stage, an advanced cleavage stage, and then the eggs embryonate. The eggs become infective in days. After ingestion (soil-contaminated hands or food), the eggs hatch in the small intestine and release larvas that mature and establish themselves as adults in the colon. The adult worms (approximately 4 cm in length) live in the cecum and ascending colon. The adult worms are fixed in that location with the anterior portions threaded into the mucosa. The females begin to oviposit days after infection. Female worms in the cecum shed between 3,000-20,000 eggs per day. The life span of the adults is about 1 year.
Most cases are asymptomatic. Heavy parasite loads cause diarrhea and pain. Diagnosis of stools is often aided by concentration techniques with a centrifuge.

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

10. Necatur americanus and Ancyclostoma duodenale
Necatur americanus and Ancyclostoma duodenale. The human hookworms include 2 nematode (roundworm) species, Ancylostoma duodenale and Necator americanus. Adult females measure mm for A. duodenale and mm for N. americanus. adult males: to 11 mm (A. duodenale), to 9 mm (N. americanus).
The life cycle follows(pic2.htm). Eggs are passed in the stool, and under favorable conditions of moisture, warmth and shade), larvas hatch in 1-2 days. The released rhabditiform larva grow in the feces and the soil, and after 5-10 days and 2 molts, they become become infective third-stage filariform larvas. These infective larvas can survive 3-4 weeks. On contact with the human host, the larvas penetrate the skin and are carried through the veins to the heart and then to the lungs. They penetrate into the pulmonary alveoli, ascend the bronchial tree to the pharynx and are swallowed. The larvas reach the small intestine, where they mature into adults. Adult worms live in the lumen of the small intestine, where they attach to the intestinal wall with resultant blood loss by the host. Most adult worms are eliminated in 1 to 2 years, but longevity records can reach several years. Some A. duodenale larvas can become dormant in the intestine or muscle.

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.
Iron deficiency anemia is the most common symptom of hookworm infection, and can be accompanied by cardiac complications. Gastrointestinal and nutritional/metabolic symptoms can also occur. In addition, local skin manifestations can occur during penetration by the filariform (L3) larvas, and respiratory symptoms can be observed during pulmonary migration of the larvas.
Microscopic identification of eggs in the stool is the most common method for diagnosing hookworm infection. The recommended procedure is as follows:
1/.Collect a stool specimen. 2/.Fix the specimen in 10% formalin. 3./Concentrate using the formalin–ethyl acetate sedimentation technique. 4./Examine a wet mount of the sediment.
Hookworm infections are generally treated with albendazole, mebendazole or pyrantel pamoate.

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.
The freeliving males and females mate, produce more larvas, and some of these larvas will develop into freeliving larvas, while other will develop into parasitic larvas. This freeliving life cycle is the reservoir for human infections.
The parasitic larvas infect the human host by penetrating the skin. They migrate to the lungs via the circulatory system and penetrate the alveoli in the small bronchioles. They are coughed up and swallowed. The larvas mature into parasitic females in the small intestine.

14. S. stercoralis also infects humans via a mechanism called "autoinfection." Under some circumstances, such as chronic constipation, larvas produced by the parasitic females will remain in the intestinal tract long enough to develop into infective stages. Such larvas will penetrate the tissues of the intestinal tract and develop as if they had penetrated the skin. Autoinfection can also occur when larvae remain on and penetrate the perianal skin. Autoinfection often leads to very high worm loads.
Since the parasitic females live in the superficial tissues of the small intestine and can be present in high numbers, they can cause significant pathology.

15. Two types of cycles exist in Strongyloides
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.
2/ Parasitic cycle: Filariform larvas in contaminated soil penetrate human skin and are transported to the lungs where they penetrate the alveolar spaces. They are carried through the bronchial tree to the pharynx where they are swallowed and then reach the small intestine. In the small intestine they molt twice and become adult female worms. The females live in the epithelium of the small intestine and by parthenogenesis produce eggs, which yield rhabditiform larvas. The rhabditiform larvas can either be passed in the stool, or in autoinfection, they transform to infective filariform larvas. These can penetrate either the intestinal mucosa (internal autoinfection) or the skin of the perianal area (external autoinfection). They can be carried successively to the lungs, the bronchial tree, the pharynx, and the small intestine where they mature into adults; or they may disseminate widely in the body.
Life cycle (pic3.htm)

16. Trichinella spiralis
Trichinella spiralis, the trichina worm, can be found in many species of carnivores and omnivores. Females are perhaps 3 mm long and males half that size. Animals are infected with T. spiralis when they ingest juvenile infective larvas in raw or undercooked meat. The larvas mature into adults in the host's small intestine in a few weeks. The female worms give birth to larvas. The males die after fertilizing the females, and they die after producing larvas.
The larvas enter the blood stream of the host and end up in the host's muscles. Here the larvas mature into infective larvas, and the next host is infected when it eats these larvas. In the muscles the larvas cause a severe host reaction that results in soreness and tenderness of the muscles. This parasite can cause extreme discomfort.
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.
The disease may include 1/ Nausea, dysentery, colic due to invasion by adult worms, 2/ Migrating juveniles cause pain as they invade muscle tissue; there may also be edema (swelling), delirium, cardiac and pulmonary difficulties, pneumonia, nervous disorders, deafness and delayed or lost reflexes, and 3/ Many cases are never diagnosed because of the vagueness of the symptoms. Muscle biopsy can be conducted and sometimes involves pressing muscle between glass plates to look for cysts. Xenodiagnosis involves feeding suspected muscle to laboratory rats.

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.
The refined aspects of life like ordinary sanitation are little considered by hungry people. A disease-ridden rural life style may remain, that is anything but comfortable.
Regardless, the eradication of many diseases is on the horizon.

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.
Certainly, we want a healthier, happier world with the amelioration of poverty partly by lessening the disease burden, but who’s going to pay for it? Is this wormy world willing to clean up the mess?