Ancylostoma spp. and Necator spp.

Hookworms, nematodes.

A food preparation and pet transferred disease.
There are many species of hookworms that infect mammals. The most important, at least from the human standpoint, are the human hookworms, Ancylostoma duodenale and Necator americanus, which infect an estimated 800,000,000 persons, and the dog and cat hookworms, A. caninum and A. braziliense, respectively.

Hookworms average about 10 mm in length and live in the small intestine of the host. The males and females mate, and the female produces eggs that are passed in the feces. Depending on the species, female hookworms can produce 10,000-25,000 eggs per day. About two days after passage the hookworm egg hatches, and the juvenile worm (or larva) develops into an infective stage in about five days.

The next host is infected when an infective larva penetrates the host's skin. The juvenile worm migrates through the host's body and finally ends up in the host's small intestine where it grows to sexual maturity. The presence of hookworms can be demonstrated by finding the characteristic eggs in the feces; the eggs can not, however, be differentiated to species.

The mouthparts of hookworms are modified into cutting plates. Attachment of hookworms to the host's small intestine causes hemorrhages, and the hookworms feed on the host's blood. Hookworm disease can have devastating effects on humans, particularly children, due to the loss of excessive amounts of blood.

Juveniles (larvae) of the dog and cat hookworms can infect humans, but the juvenile worms will not mature into adult worms. Rather, the juveniles remain in the skin where they continue to migrate for weeks (or even months in some instances). This results in a condition known as "cutaneous" or "dermal larval migrans" or "creeping eruption." Hence the importance of not allowing dogs and cats to defecate indiscriminately.

Hookworms are the voracious blood feeders of the nematode world. In the order Strongylida and superfamily Ancylostomatoidea are the two principal species of hookworms which infect humans.

  • Ancylostoma duodenale:
    - Africa, India, China and South East Asia; longevity to 5 years

  • Necator americanus:
    - First reported in Brazil, then Texas, but since found in Africa, India and South East Asia; longevity to 15 years.

Two other species, A. cylanicum found in Sri Lanka and A. braziliense found in Brazil, are both mainly found infecting carnivores, but have occasionally been reported to infect humans. In addition, species such as A. caninum which infect dogs and A. tubeforme which parasitize cats are also an important cause of larval migrans in humans.

Life Cycle
These nematodes have a direct life cycle which is similar for both species, with minor modifications.

The adult worms release eggs into the intestinal lumen, which, by the time they leave the host, have only developed as far as the 4 or 8-cell stage. Once outside the host, depending on the temperature, they can hatch within 24 to 48 hours. The eggs are relatively thin walled and require warm moist shaded conditions for embryonation. The eggs are susceptible to killing by frost or dehydration but also require oxygen for hatching and development thus they require light loamy soils.

The released rhabdiform L1 larvae requires 2-3 days before it molts to the L2 stage and the second molt occurs after a further 5 days, producing the ensheathed infective third stage larva. The L3 are non-feeding active stages which move to the periphery of the faecal mass or into the soil, where they can remain active and infective for up to three weeks, depending on the climatic conditions.

Hookworms require a moist, fairly cool environment to survive and develop as free-living organisms. The survival temperature range is usual within 17-30 C. Larvae will not develop below 17 C. The larval food reserves are stored in the form of unbound neutral lipid, and their rate of utilization may be the limiting factor which determines the duration of larval infectivity. When conditions are moist and humid, the larvae migrate to the top of the soil or faecal mass and undergo a behaviour known as nictating. During this process the worm almost stands on its tail and waves its head around, which presumable increases their chance of contacting the host.

The larvae effectively exsheath at this point, the sheath still acts as an extra layer of protection against desiccation, and the worms can retract into it in between period of nictating. However, once a host is contacted, the larvae leave the sheath behind.

Hookworms are sensitive to carbon dioxide and also changes in temperature and on contact with a warm-blooded host penetrate rapidly into the skin, orienting to the thermal gradient that exists across the skin. In addition, skin lipids are also known to be important stimuli for the penetration process.

Necator americanus is aided in the process of penetration by the release of proteolytic enzymes, released by the pharyngeal glands, whereas the Ancylostoma sp. appear to rely on mechanical penetration only.

Once they have entered the skin, the larvae pass into the blood capillaries from where they are carried to the lungs. Reaching the lungs, the larvae burst into the alveolar spaces, where they undergo the next molt to the L4 stage. After a period of development in the lungs, the L4 migrate up the trachea and are swallowed and pass down the oesophagus, through the stomach and into the small intestine. Here they undergo the final molt to produce the young adult stages.

The adult hookworms attach to the mucosa of the small intestine with their powerful modified stoma, abrading the mucosa until they puncture the blood capillaries and can suck the host blood. Heavy hookworm infections can account for as much as 200 ml of blood loss per day.

Individuals become infected, usually by walking bare footed across contaminated soil. Soil contamination can be extremely heavy, particularly in those cultures which utilise human excreta, known as Night soil, as fertilizer. The eggs are susceptible to urine however, and it has been found that if faecal material is mixed with urine the eggs can be killed.

There has also been the suggestion that juveniles can survive in the muscles of an abnormal paratenic host and can resume normal development when the infected meat is eaten raw or poorly cooked.

There are three pathological phases to hookworm infections:

  1. Cutaneous or invasive phase: When larvae initially penetrate the skin they can cause irritation and itching and if they fail to locate a blood capillary they can wander through the skin causing a condition known as cutaneous larval migrans, leaving a track visualized under the skin by the presence of the host inflammatory reaction.

  2. Pulmonary phase: This occurs during the period when the larvae are bursting out of the capillaries in the lungs into the alveolar spaces. This causes local haemorrhaging at the site. This is rarely symptomatic, except when there is a heavy infection, when it can result in pneumonitis, and can also cause a cough and a sore throat.

  3. Intestinal phase: Adult worms are usually restricted to the anterior third of the small intestine, but where infections are very heavy they can occupy the whole length of the small intestine. The worms clamp onto the mucosa abrading the surface and sucking the blood. Proteolytic enzymes from the dorsal pharyngeal gland are released into the buccal cavity which aid in digestion.

The most common effect from hookworm infections is the varying degrees of anaemia, depending on the level of the infection and the nutritional state of the patient. Patients also can suffer from protein deficiency which is manifest as dry hair, skin and edema, but protein loss can have far reaching effects including reduced immunocompetence and reduced ability to produce gama globulin (Antibody).

The infection is particularly severe in children, and the development of a pot belly, as a result of the edema, is a common symptom of the infection. The protein deficiency also can result in significantly delayed physical development in children. In its most progressive state can result in death.

Although malabsorption is not associated with hookworm disease, the combination of malnutrition and other concomitant infections, such as trichuris, or ascariasis, or even malaria, can exacerbate and complicate the disease picture.

As previously mentioned the pathology due to hookworm infection is related to the intensity of infection, and can be readily demonstrated with N. americanus infections. As shown in the following example:

  • 25 worms no symptoms
  • 25-100 worms Mild symptoms, anaemia
  • 100-500 worms Considerable damage, moderate symptoms
  • 500-1000 worms severe symptoms, with severe pathology, often fatal consequences.

A. duodenale, on the other hand, appear to be much more pathogenic, as few as 100 adult worms can result in severe symptoms, normally associated with a much heavier worm burden in Necator infections.

The appearance of eggs or larvae in the stool is the principal method of diagnosis. Reliable detection of the eggs in the faeces usually requires the use of one of the faecal egg concentration techniques. For the purpose of treatment it is not necessary to distinguish between N. americanus and A. duodenale, which is just as well as the eggs and larvae look identical. However, if one is interested in studying the efficacy of drug treatment on the two species then the only real way to differentiate between them is to collect the adults which are voided by the host after treatment. The species can be readily identified by virtue of the differences in their mouth parts.

The drug of choice for the treatment of hookworm disease is mebendazole which is effective against both species, and in addition, will remove the intestinal worm Ascaris also, if present. The drug is very efficient, requiring only a single dose and is inexpensive, the perfect drug. However, treatment requires more than giving the anthelmintic, the patient should also receive dietary supplements to improve their general level of health, in particular iron supplementation is very important. Iron is an important constituent of a multitude of enzyme systems involved in energy metabolism, DNA synthesis and drug detoxification.

As mentioned earlier larval migrans or as it is also known, creeping eruption, is also a very uncomfortable symptom of this disease, and can also be caused by invasion of hookworms from other animals such as cats and dogs. Because they are in an abnormal host they do not mature to adults but instead migrate through the skin until killed by the host's inflammatory response. This causes local intense itching. Topical treatment with thiabendazole ointment is very effective in controlling this condition.

Control of this parasite should be directed against reducing the level of environmental contamination. Treatment of heavily infected individuals is one way to reduce the source of contamination (one study has estimated that 60% of the total worm burden resides in less than 10% of the population). Other obvious methods are to improve sanitary condition, e.g.. latrines, but also convincing people to use them by maintaining them in a serviceable form making them conducive to use. Hookworms still account for high proportion of debilitating disease in the tropics and 50-60,000 deaths per year can be attributed to this disease.

Hypobiosis - arrested development:
Hypobiosis refers to an arrested or dormant state which larvae assume once they have entered the host but have not yet completed their development to adults. The advantage of this biological process is usually to prevent the next generation of eggs and larvae from either being exposed to unfavourable environmental conditions or to make sure that the next generation of infective stages is present in the environment during the period when susceptible young hosts are available.

In hookworm infections, seasonal hypobiosis serves to synchronize the parasites development with external seasonal conditions, such that the eggs will be produced during the wet season, when they are capable of completing their development.

Hypobiosis is characterized by reduced metabolic activity in the arrested larva, and can last up to about 8 months. During this period, the arrested larvae have a reduced susceptibility to drug treatment.

Evidence for arrested development in hookworm infections comes from epidemiological studies which have shown that there is a sudden significant increase in adult worm burdens just following the dry season, when there are no longer any infective stages in the soil. This can only be accounted for by the presence of arrested larvae in the patients.

Recent figures taken indicate that 90% of all adults in the United States host some form of parasitic organism at any one time.

“I find parasites in 92% of people. Everybody - rich and poor - the whole population have parasites . . . Pets are great carriers of parasites. Also, vegetables may carry parasitic organisms." Dr. William Kelly, famous cancer specialist. “One of every four people in the world is infected with roundworms, which cause fever, cough and intestinal problems. A quarter of the world's people have hookworms, which can cause anaemia and abdominal pain. Another third of a billion people suffer from abdominal pain and diarrhoea caused by whipworms.” The Miami Herald, June 25 1978.

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The common hookworm is passed through the dog's feces and deposited into the soil. The parasites then stay in the soil where they will eventually hatch into larvae that can penetrate through the skin or be ingested. These worms are not usually affected by extreme environmental conditions so they can be a problem in any area of the world.

Hookworms become a problem for children when the child plays with the infected dog and comes into contact with the feces. This can occur when the dog has defecated and some of the feces is still on the hair or skin. This feces is then transmitted to the mouth by way of unwashed hands.

Another way children can become infected is if they walk barefoot in grass or sand where a dog has defecated. Younger children are at risk when they put dirt or sand into their mouths while playing.

In children (or adults) who walk barefoot, the hookworm can penetrate the sole of the foot and cause a lesion. The larva will then begin to mature while it moves towards the intestines. As in dogs, the hookworm will attach to the intestinal wall. Humans who have become infected will show symptoms of intestinal bleeding, abdominal pains, anaemia, sever diarrhoea and malnutrition. ...

Author: David R Haburchak, MD, Program Director, Professor, Department of Internal Medicine, Division of Infectious Disease, Medical College of Georgia

Hookworm is a widespread and clinically important human nematode infection. Prevalence figures indicate that Ancylostoma duodenale and Necator americanus infect more than 1 billion people and produce morbidity from anaemia in more than 96 million. Hookworms impair the physical and intellectual development of children and the economic development of communities.

Infection is acquired through skin exposure to larvae in soil contaminated by human feces. Soil becomes infectious about 9 days after contamination and remains so for about 2 weeks. Individual treatment consists of iron replacement and anthelmintic therapy.

Necator and Ancylostoma adults are roundworms that range from 5-13 mm long. Females release thousands of eggs into stool daily. In sandy, moist soil, eggs hatch and must molt twice before developing into third-stage larvae.

Third-stage larvae are 500-700 m m long and are capable of rapid penetration into normal skin, most commonly of the feet. Transmission occurs after 5 or more minutes of skin contact with soil containing viable larvae. They puncture and feed on mucosal capillaries in the jejunum. Ground itch at the site of penetration is more common with Ancylostoma species than with Necator.

The larvae burrow into venules and embolize the lungs, where they break into alveoli. A mild and usually asymptomatic alveolitis with eosinophilia ensues. (Hookworm is one of the causes of the pulmonary infiltrates and eosinophilia [PIE] syndrome, along with Ascaris and Strongyloides species.) Coughing brings the larvae to the mouth, where swallowing transports them to the intestine. Approximately 5 weeks after skin penetration, adult females begin to produce eggs.

Ancylostoma larvae may also infect via ingestion, but they do not migrate into the body in this instance. This worm may lie dormant in tissues and later be transmitted through breast milk. Neither worm multiplies within the host. If the host is not re exposed, the infection will disappear after the worm dies. Necator has a 5-year lifespan; Ancyclostoma has a 1-year lifespan.

Necator ingests 0.03 mL of blood per worm per day; Ancylostoma ingests 0.20 mL blood per worm per day. Subsequent host anaemia is proportional to diet, iron reserves, and worm burden. Threshold worm loads for anaemia differ nationally, with as few as 40 worms producing anaemia in countries with low iron consumption. In the 19th century, an autopsy of an Italian tunnel worker who died of anaemia revealed 1500 worms. Before worker sanitation was enforced, epidemic hookworm infection was common in mines and tunnels in Europe. Severe anaemia affects the intellectual and physical development of children and the cardiovascular performance of adults.

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The above is a collection of a FEW details to afford an awareness and appreciation of this form of parasite. There are many species which share background, life cycle, pathology, symptoms, and treatment and differ only by name and location. The above are examples of common patterns. There are MANY more resources in libraries and on the Internet which you can review if you have further interest.

GLOBALIZATION: While many species of parasite are restricted to a specific geographical location, there is a frequent interchange of business and recreational travelers between these and most other regions. What is picked up in one location by a host will be preserved by the internal environment of that host in another foreign and even hostile external environment, until it is terminated.

Digestive elimination of stool in other locations will, in some cases, contribute to the spread of the species. This has happened many times before and of a relative frequency connected to the numbers of persons and amount of traffic occurring internationally. Most flu viruses originate in China. They are often experienced worldwide within weeks of the initial outbreak.

PRECAUTIONS, as with other parasites, include NOT walking barefoot and not swimming in contaminated waters. Ensure that all raw vegetables are washed in uncontaminated water as they may carry infected soil or dust, especially if they have been organically grown. In larger scale agricultural operations, green fertilizer (manure) is usually "cleansed" through fermentation in a storage pile or stack, mixed with straw or other compost. This is often an excluded or minimized step in smaller plot use.

Urbanized supply of foods in supermarkets or in restaurants and through fast food outlets provides a constant opportunity for food to be handled by staff or consumer and prepared by persons who have insufficiently washed their hands following contact with infected dogs or cats, contaminated parkland or lawn grass, or contact with public surfaces used as seating, tables, or hand railings. If clothing has contacted contaminated surfaces, hand wahsing may provide only temporary benefit until the wearer touches their clothing to wipe their hand, rub an itch, or adjust it.

There will be less risk in these environments if you wash purchased food in clean water, peel it whenever possible, cook it, and add anti-worm spices to it (see below). Remember that it is increasingly difficult to find municipal or rural water supplies which are not contaminated. Fresh vegetable and fruit juices provide a high degree of safety through their enzyme content.

Size, longevity, and quality of enterprise can be an indicator of food safety. Franchise operations often encourage high standards of sanitary food preparation. Street vendors, sole proprietorships, and low cost ethnic restaurants more often violate sanitary precautions than franchisees. Washroom cleanliness is often an indication of kitchen staff standards.

In intimate relationships there is some opportunity for the infection to spread between individuals. Some species of hookworms spread from the lungs through the throat into the digestive system and to the intestines. Passing through the throat, they may be coughed up or otherwise brought into and carried temporarily by the saliva. Intimate kissing often involved the mixing and exchange of the saliva of the individuals involved. IF the non-infected person receives contamination in the saliva transfer, they MAY become infected.

DIET - Periodically consume curry meals (highly anti-parasitic) followed by probiotics treatment (to re-establish healthy intestinal flora). If the latter is NOT your usual diet, expect to be ill for 2 to 4 days for this cycle. Other spices of benefit include tumeric, cinnamon, cloves, garlic, hot peppers. Use of coconut oil in place of other cooking oils as well as replacing butter and margarine is also a benefit.

It is a realistic approach to EXPECT to become infected by destructive parasites and to undergo a periodic (i.e. annual) parasitic cleanse, as most fresh waters globally located near human habitation ARE polluted. CDC estimates that 65 to 95% of human use (recreational, washing, drinking) waters are contaminated at any given time. PLANNING can minimize periods of lost productivity and lengthy periods of distress and ill health.

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Parasite INDEX