Parasitic worm

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Eggs of different species of parasitic worm Collage of various helminth eggs.png
Eggs of different species of parasitic worm

Parasitic worms, also known as helminths, [1] are a polyphyletic group of large macroparasites; adults can generally be seen with the naked eye. Many are intestinal worms that are soil-transmitted and infect the gastrointestinal tract. Other parasitic worms such as schistosomes reside in blood vessels.

Contents

Some parasitic worms, including leeches and monogeneans, are ectoparasites  – thus, they are not classified as helminths, which are endoparasites.

Parasitic worms live in and feed in living hosts. They receive nourishment and protection while disrupting their hosts' ability to absorb nutrients. This can cause weakness and disease in the host, and poses a global health and economic problem. [2] Parasitic worms cannot reproduce entirely within their host's body; they have a life cycle that includes some stages that need to take place outside of the host. [3] Helminths are able to survive in their mammalian hosts for many years due to their ability to manipulate the host's immune response by secreting immunomodulatory products. [4] All parasitic worms produce eggs during reproduction. These eggs have a strong shell that protects them against a range of environmental conditions. The eggs can therefore survive in the environment for many months or years.

Many of the worms referred to as helminths are intestinal parasites. An infection by a helminth is known as helminthiasis, helminth infection, or intestinal worm infection. There is a naming convention which applies to all helminths: the ending "-asis" (or in veterinary science: "-osis") is added at the end of the name of the worm to denote the infection with that particular worm.[ citation needed ] For example, Ascaris is the name of a type of helminth, and ascariasis is the name of the infection caused by that helminth.

Taxonomy

Hookworms attached to the intestinal mucosa Hookworms.JPG
Hookworms attached to the intestinal mucosa
Two pinworms Threadworm.jpg
Two pinworms
Image showing life cycle inside and outside of the human body of one fairly typical and well described helminth: Ascaris lumbricoides Ascaris lumbricoides life cycle.tif
Image showing life cycle inside and outside of the human body of one fairly typical and well described helminth: Ascaris lumbricoides

Helminths are a group of organisms which share a similar form but are not necessarily evolutionarily related. The term "helminth" is an artificial term. [5] [6] There is no real consensus on the taxonomy (or groupings) of the helminths, particularly within the nematodes. [7] The term "helminth" contains a number of phyla, many of which are completely unrelated. However, for practical considerations the term is currently used to describe four phyla with superficial similarities: Annelida (ringed or segmented worms), Platyhelminthes (flatworms), Nematoda (roundworms), and Acanthocephala (thorny-headed worms). [7] The phylum Platyhelminthes includes two classes of worms of particular medical significance: the cestodes (tapeworms) and the trematodes (flukes and blood flukes), depending on whether or not they have segmented bodies. [1] [8]

There may be as many as 300,000 species of parasites affecting vertebrates, [9] and as many as 300 affecting humans alone. [10]

Helminths of importance in the sanitation field are the human parasites, and are classified as Nemathelminthes (nematodes) and Platyhelminthes, depending on whether they possess a round or flattened body, respectively. [8]

Ringworm (dermatophytosis) is actually caused by various fungi, and not by a parasitic worm. [11] [12]

Reproduction and life cycle

The lifetime of adult worms varies tremendously from one species to another but is generally in the range of 1 to 8 years (see following table). This lifetime of several years is a result of their ability to manipulate the immune response of their hosts by secreting immunomodulatory products. [4]

Helminths can be either hermaphroditic (having the sex organs of both sexes), like tapeworms and flukes (not including the blood fluke), or have their sexes differentiated, like the roundworms. [13] All helminths produce eggs (also called ova) for reproduction. [14]

Eggs

Generally, thousands or even hundreds of thousands of eggs are produced each time the female worm deposits its eggs - a process called oviposition. There is a large variation in the number of eggs produced by different species of worm at one time; it varies in the range of 3,000 to 700,000. The frequency of egg deposition from an adult helminth is generally daily, and can occur up to six times per day for some Taenia species. Adult trematodes lay smaller numbers of eggs compared to cestodes or nematodes. However, the egg develops into a miracidia from which thousands of cercariae , or swimming larvae, develop. This means that one egg may produce thousands of adult worms. [15] Helminth eggs remain viable for 1–2 months in crops and for many months in soil, fresh water, and sewage, or even for several years in feces, fecal sludge (historically called night soil), and sewage sludge – a period that is much longer compared to other microorganisms. [16] [17]

Helminth eggs are resistant to various environmental conditions due to the composition of the egg shell. Each helminth egg species has 3 to 4 layers with different physical and chemical characteristics: [13]

  1. the 1 to 2 outer layers are formed of mucopolysaccharides and proteins,
  2. the middle layers consist of chitinous material and serve to give structure and mechanical resistance to the eggs, and
  3. the inner layer is composed of lipids and proteins and is useful to protect eggs from desiccation, strong acid and bases, oxidants and reductive agents as well as detergent and proteolytic compounds. [18] [19] [20] [21]

Larvae

Larvae hatch from eggs, either inside or outside the host, depending on the type of helminth. For eggs in moist soil at optimal temperature and oxygen levels, the embryo develops into an infective larva after 2 to 4 weeks, named "second-stage larva". Once ingested by a host, this larva has the ability to get out of the egg, hatch in the small intestine and migrate to different organs. These infective larvae (or "infective eggs") may remain viable in soil for two years or longer. [22]

The process of larval maturation in the host can take from about two weeks up to four months, depending on the helminth species.[ citation needed ]

The following table shows the principal morphological and reproductive distinctions for three helminth groups:

Tapeworms
(Cestodes)		Flukes
(Trematodes)		Roundworms
(Nematodes)
Examples Taenia solium, Taenia saginata, Hymenolepis spp., Echinococcus granulosus, Echinococcus multilocularis , Multiceps multiceps Schistosoma mansoni , Schistosoma japonicum ,

Fasciola hepatica

Ascaris spp. , Enterobius, Filarioidea, Onchocerca spp. , Rhabditis spp., Trichuris spp., Necator americanus , Ancylostoma spp.
Pathological conditions caused in humans Tapeworm infection, echinococcosis, alveolar echinococcosis Schistosomiasis, swimmer's itch Ascariasis, enterobiasis (pinworm infection, oxyuriasis), filariasis, dracunculiasis (guinea worm), elephantiasis, enterobiasis (pinworm), filariasis, hookworm infection (includes Necatoriasis and Ancylostoma duodenale infection), onchocerciasis, trichinosis, trichuriasis (whipworm)
ShapeSegmented planeUnsegmented planeCylindrical
Body cavity NoneNonePresent
Body covering Tegument Tegument Cuticle
Digestive tubeNoneEnds in cecumEnds in anus
Sex Hermaphroditic Hermaphroditic, except schistosomes which are dioecious Dioecious
Attachment organs Sucker or bothridia, and rostellum with hooksOral sucker and ventral sucker or acetabulum Lips, teeth, filariform extremities, and dentary plates

Number of species

6000 [23] Estimated > 15,000 [24] Registered > 9,000 [25] Estimated > 800,000 to 1,000,000

Registered > 25,000 [24]

Number of species known to infect humans40 [23] 16 [24] > 12,000 [24]
Species

Hymenolepis nana

Taenia solium /Taenia saginata

Fasciola hepatica

Ascaris lumbricoides

Hookworm

Trichuris trichiura

Toxocara spp.
Timeline of lifecycle stagesLarval formation

Some days (eggs can survive for months) [26]

9–15 days [23]

18 days to several weeks [27]

1–2 days [28]

15–30 days [29]

Larval growth

After hatching, the larvae develop into cysticercoid, which can survive for years in an animal [26]

5–7 weeks as cercariae in snails and longer periods in wet environments as encysted metacercariae [15]

10–14 days [27]

5–10 days (after maturing can survive for weeks outside the host) [28]

60–70 days (from hatching to mature state) [29]

5–6 days [23]

Maturation to adult

2 months (from cysticercoid to adult) [26]

3–4 months [15]

2–3 months [27]

2–8 weeks [23] (can become dormant for months)

Lifespan of adult worm

4–6 weeks

Several years [26]

8–10 years [23]

1–2 years [27]

Several years [28]

1 year [29]

Eggs laid per day250,000 [3] to 700,000 [23] 3,000 to 25,000 [24] 3,000 [3] to 250,000 [23]
Egg depositionFrequency

up to 6 times a day [26]

daily [27]

daily [28]

daily [29]

Number of eggs per event

50,000-100,000 [26]

200,000 [27] [22] to 250,000 or more [23]

5,000-10,000 [23]

3,000-20,000 [29]

Larvae per egg11300 cercariae ( Schistosoma ), 250,000 metacercariae ( Fasciola ) [24] 1111

Draft genomes for all categories of helminth have been sequenced in recent years and are available through the ParaSite sub-portal of WormBase. [30]

Use in medicine

Parasitic worms have been used as a medical treatment for various diseases, particularly those involving an overactive immune response. [31] As humans have evolved with parasitic worms, proponents argue they are needed for a healthy immune system. [31] Scientists are looking for a connection between the prevention and control of parasitic worms and the increase in allergies such as hay-fever in developed countries. [31] Removal of parasitic worms from areas is correlated with an increase in autoimmune disorders in those areas. [32] Parasitic worms may be able to damp down the immune system of their host, making it easier for them to live in the intestine without coming under attack. [31] This may be one mechanism for their proposed medicinal effect.[ citation needed ]

One study suggests a link between the rising rates of metabolic syndrome in the developed worlds and the largely successful efforts of Westerners to eliminate intestinal parasites. The work suggests eosinophils (a type of white blood cell) in fat tissue play an important role in preventing insulin resistance by secreting interleukin 4, which in turn switches macrophages into "alternative activation". Alternatively-activated macrophages are important to maintaining glucose homeostasis (i.e., blood sugar regulation). Helminth infection causes an increase in eosinophils. In the study, the authors fed rodents a high-fat diet to induce metabolic syndrome, and then injected them with helminths. Helminth infestation improved the rodents' metabolism. [33] The authors concluded:

Although sparse in blood of persons in developed countries, eosinophils are often elevated in individuals in rural developing countries where intestinal parasitism is prevalent and metabolic syndrome rare. We speculate that eosinophils may have evolved to optimize metabolic homeostasis during chronic infections by ubiquitous intestinal parasites…. [33]

Human stool samples

For medical purposes, the exact number of helminth eggs is less important and therefore most diagnoses are made simply by identifying the appearance of the worm or eggs in feces. Due to the large quantity of eggs laid, physicians can diagnose using as few as one or two fecal smears.[ citation needed ] The Kato technique (also called the Kato-Katz technique) is a laboratory method for preparing human stool samples prior to searching for parasite eggs. Eggs per gram is a laboratory test that determines the number of eggs per gram of feces in patients suspected of having a parasitological infection, such as schistosomiasis.[ citation needed ]

Relevance for sanitation

Processed helminth eggs samples from a dry toilet in Kenya Processed helminth eggs samples and Mc Master slide (4369782501).jpg
Processed helminth eggs samples from a dry toilet in Kenya
Analysing for helminth eggs in samples of feces from a dry toilet in Kenya Helminth Eggs determination (in faeces) (4369783299).jpg
Analysing for helminth eggs in samples of feces from a dry toilet in Kenya

Helminth eggs can reach the soil when polluted wastewater, sewage sludge or human waste are used as fertilizer. Such soil is often characterized by moist and warm conditions. Therefore, the risk of using contaminated wastewater and sludge in agricultural fields is a real problem, especially in poor countries, where this practice is prevalent. [18] [34] Helminth eggs are regarded as the main biological health risk when applying sewage sludge, fecal sludge or fecal matter on agricultural soils. [16] The eggs are the infective stage of the helminths’ life cycle for causing the disease helminthiasis.[ citation needed ]

Due to this strong shell, helminth eggs or ova remain viable in soil, fresh water and sewage for many months. In feces, fecal sludge and sewage sludge they can even remain viable for several years. [16] [17] Helminth eggs of concern in wastewater used for irrigation have a size between 20 and 90 μm and a relative density of 1.06–1.23. [18] It is very difficult to inactivate helminth eggs, unless temperature is increased above 40 °C or moisture is reduced to less than 5%. [18] Eggs that are no longer viable do not produce any larvae. In the case of Ascaris lumbricoides (giant roundworm), which has been considered the most resistant and common helminth type, fertilized eggs deposited in soil are resistant to desiccation but are, at this stage of development, very sensitive to environmental temperatures: The reproduction of a fertilized egg within the eggshell develops at an environmental soil temperature about 25 °C which is lower than the body temperature of the host (i.e., 37 °C for humans). [22] However, development of the larvae in the egg stops at temperatures below 15.5 °C, and eggs cannot survive temperatures much above 38 °C. If the temperature is around 25 °C, the infectiousness occurs after nearly 10 days of incubation. [8] [35] [36]

Removal versus inactivation

Processes that remove particles, such as sedimentation, filtration or coagulation-flocculation physically remove helminth eggs from wastewater (but do not inactivate them). [37] [38] Therefore, waste stabilization ponds (lagoons), storage basins, constructed wetlands, rapid filtration or upflow anaerobic sludge blanket (UASB) reactors can be used.

Helminth ova cannot be inactivated with chlorine, UV light or ozone (in the latter case at least not with economical doses because >36 mg/L ozone are needed with 1 hour contact time).[ citation needed ]

Helminth ova can be inactivated in sewage sludge treatment if the temperature is increased over 40 °C or moisture is reduced to less than 5%. [18] Best results can be obtained when both of these conditions are met together for an extended period of time. [39] Details about the contact time under these conditions and other related environmental factors are generally not well-defined for every type of helminth egg species. [8] Helminth eggs are considered highly resistant biological structures. [18]

Measurements

Indicator organism

Identification and quantification of helminth eggs at UNAM university in Mexico City, Mexico Identification and quantification of helminth eggs.png
Identification and quantification of helminth eggs at UNAM university in Mexico City, Mexico
This section is an excerpt from Indicator organism § Indicator helminth eggs.[ edit ]

The eggs from helminths (parasitic worms) are a commonly used indicator organism to assess the safety of sanitation and wastewater reuse systems (such schemes are also called reuse of human excreta). [40] : 55  This is because they are the most resistant pathogens of all types of pathogens (pathogens can be viruses, bacteria, protozoa and helminths). [41] It means they are relatively hard to destroy through conventional treatment methods. They can survive for 10–12 months in tropical climates. [41] These eggs are also called ova in the literature. [42]

Helminth eggs that are found in wastewater and sludge stem from soil-transmitted helminths (STHs) which include Ascaris lumbricoides (Ascaris), Anclostoma duodenale , Necator americanus (hookworm), and Trichuris trichiura (whipworm). [43] Ascaris and whipworm that are identified in reusable wastewater systems can cause certain diseases and complications if ingested by humans and pigs. [44] Hookworms will plant and hatch their larvae into the soil where they grow until maturity. Once the hookworm eggs are fully developed, they infect organisms by crawling through the organism’s skin. [45]

The presence or absence of viable helminth eggs ("viable" meaning that a larva would be able to hatch from the egg) in a sample of dried fecal matter, compost or fecal sludge is often used to assess the efficiency of diverse wastewater and sludge treatment processes in terms of pathogen removal. [40] : 55  In particular, the number of viable Ascaris eggs is often taken as an indicator for all helminth eggs in treatment processes as they are very common in many parts of the world and relatively easy to identify under the microscope. However, the exact inactivation characteristics may vary for different types of helminth eggs. [46]

The technique used for testing depends on the type of sample. [42] When the helminth ova are in sludge, processes such as alkaline-post stabilization, acid treatment, and anaerobic digestion are used to reduce the amount of helminth ova in areas where there is a large amount. These methods make it possible for helminth ova to be within the healthy requirements of ≤1 helminth ova per liter. Dehydration is used to inactivate helminth ova in fecal sludge. This type of inactivation occurs when feces is stored between 1-2 years, a high total solids content (>50-60%) is present, items such as leaves, lime, earth, etc. are added, and at a temperature of 30°C or higher. [45]

Environmental samples

For the purpose of setting treatment standards and reuse legislation, it is important to be able to determine the amount of helminth eggs in an environmental sample with some accuracy. The detection of viable helminth eggs in samples of wastewater, sludge or fresh feces (as a diagnostic tool for the infection helminthiasis) is not straight forward. In fact, many laboratories in developing countries lack the right equipment or skilled staff required to do so. An important step in the analytical methods is usually the concentration of the eggs in the sample, especially in the case of wastewater samples. A concentration step may not be required in samples of dried feces, e.g. samples collected from urine-diverting dry toilets.[ citation needed ]

See also

Related Research Articles

<i>Ascaris lumbricoides</i> One of several species of Ascaris

Ascaris lumbricoides is a large parasitic roundworm of the genus Ascaris. It is the most common parasitic worm in humans. An estimated 807 million–1.2 billion people are infected with A. lumbricoides worldwide. People living in tropical and subtropical countries are at greater risk of infection. Infection by Ascaris lumbricoides is known as ascariasis.

<i>Trichuris trichiura</i> Parasitic roundworm that causes intestinal infection

Trichuris trichiura, Trichocephalus trichiuris or whipworm, is a parasitic roundworm that causes trichuriasis when it infects a human large intestine. It is commonly known as the whipworm which refers to the shape of the worm; it looks like a whip with wider "handles" at the posterior end. The helminth is also known to cause rectal prolapse.

<span class="mw-page-title-main">Trichuriasis</span> Infection by Trichuris trichiura (whipworm)

Trichuriasis, also known as whipworm infection, is an infection by the parasitic worm Trichuris trichiura (whipworm). If infection is only with a few worms, there are often no symptoms. In those who are infected with many worms, there may be abdominal pain, fatigue and diarrhea. The diarrhea sometimes contains blood. Infections in children may cause poor intellectual and physical development. Low red blood cell levels may occur due to loss of blood.

<span class="mw-page-title-main">Intestinal parasite infection</span> Condition in which a parasite infects the gastro-intestinal tract of humans and other animals

An intestinal parasite infection is a condition in which a parasite infects the gastro-intestinal tract of humans and other animals. Such parasites can live anywhere in the body, but most prefer the intestinal wall.

<span class="mw-page-title-main">Parasitic disease</span> Medical condition

A parasitic disease, also known as parasitosis, is an infectious disease caused by parasites. Parasites are organisms which derive sustenance from its host while causing it harm. The study of parasites and parasitic diseases is known as parasitology. Medical parasitology is concerned with three major groups of parasites: parasitic protozoa, helminths, and parasitic arthropods. Parasitic diseases are thus considered those diseases that are caused by pathogens belonging taxonomically to either the animal kingdom, or the protozoan kingdom.

<span class="mw-page-title-main">Ascariasis</span> Disease caused by the parasitic roundworm Ascaris lumbricoides

Ascariasis is a disease caused by the parasitic roundworm Ascaris lumbricoides. Infections have no symptoms in more than 85% of cases, especially if the number of worms is small. Symptoms increase with the number of worms present and may include shortness of breath and fever in the beginning of the disease. These may be followed by symptoms of abdominal swelling, abdominal pain, and diarrhea. Children are most commonly affected, and in this age group the infection may also cause poor weight gain, malnutrition, and learning problems.

<span class="mw-page-title-main">Helminthiasis</span> Any macroparasitic disease caused by helminths

Helminthiasis, also known as worm infection, is any macroparasitic disease of humans and other animals in which a part of the body is infected with parasitic worms, known as helminths. There are numerous species of these parasites, which are broadly classified into tapeworms, flukes, and roundworms. They often live in the gastrointestinal tract of their hosts, but they may also burrow into other organs, where they induce physiological damage.

<span class="mw-page-title-main">Hookworm infection</span> Disease caused by intestinal parasites

Hookworm infection is an infection by a type of intestinal parasite known as a hookworm. Initially, itching and a rash may occur at the site of infection. Those only affected by a few worms may show no symptoms. Those infected by many worms may experience abdominal pain, diarrhea, weight loss, and tiredness. The mental and physical development of children may be affected. Anemia may result.

<i>Necator americanus</i> Species of hookworm

Necator americanus is a species of hookworm commonly known as the New World hookworm. Like other hookworms, it is a member of the phylum Nematoda. It is an obligatory parasitic nematode that lives in the small intestine of human hosts. Necatoriasis—a type of helminthiasis—is the term for the condition of being host to an infestation of a species of Necator. Since N. americanus and Ancylostoma duodenale are the two species of hookworms that most commonly infest humans, they are usually dealt with under the collective heading of "hookworm infection". They differ most obviously in geographical distribution, structure of mouthparts, and relative size.

<i>Ascaris suum</i> Species of roundworm

Ascaris suum, also known as the large roundworm of pig, is a parasitic nematode that causes ascariasis in pigs. While roundworms in pigs and humans are today considered as two species with different hosts, cross-infection between humans and pigs is possible; some researchers have thus argued they are the same species. Ascariasis is associated with contact to pigs and pig manure in Denmark.

<i>Ascaris</i> Genus of roundworms

Ascaris is a nematode genus of parasitic worms known as the "small intestinal roundworms". One species, Ascaris lumbricoides, affects humans and causes the disease ascariasis. Another species, Ascaris suum, typically infects pigs. Other ascarid genera infect other animals, such as Parascaris equorum, the equine roundworm, and Toxocara and Toxascaris, which infect dogs and cats.

<span class="mw-page-title-main">Helminthic therapy</span> Deliberate infestation with parasitic worms

Helminthic therapy, an experimental type of immunotherapy, is the treatment of autoimmune diseases and immune disorders by means of deliberate infestation with a helminth or with the eggs of a helminth. Helminths are parasitic worms such as hookworms, whipworms, and threadworms that have evolved to live within a host organism on which they rely for nutrients. The theory behind helminth therapy is that these worms reduce negative immune responses due to their TH2 immune response that downregulates the abnormal T-cell responses recently associated with autoimmune disorders. This therapy ties to the Hygiene hypothesis in that the lack of exposure to bacteria and parasites such as helminths can cause a weaker immune system leading to being more susceptible to autoimmune disease.

<i>Trichuris</i> Genus of roundworms

Trichuris, often referred to as whipworms or the silent serpent, is a genus of parasitic helminths from the roundworm family Trichuridae. The name whipworm refers to the shape of the worm; they look like whips with wider "handles" at the posterior end.

<i>Toxocara canis</i> Species of roundworm

Toxocara canis is a worldwide-distributed helminth parasite that primarily infects dogs and other canids, but can also infect other animals including humans. The name is derived from the Greek word "toxon," meaning bow or quiver, and the Latin word "caro," meaning flesh. T. canis live in the small intestine of the definitive host. This parasite is very common in puppies and somewhat less common in adult dogs. In adult dogs, infection is usually asymptomatic but may be characterized by diarrhea. By contrast, untreated infection with Toxocara canis can be fatal in puppies, causing diarrhea, vomiting, pneumonia, enlarged abdomen, flatulence, poor growth rate, and other complications.

Indicator organisms are used as a proxy to monitor conditions in a particular environment, ecosystem, area, habitat, or consumer product. Certain bacteria, fungi and helminth eggs are being used for various purposes.

<i>Toxascaris leonina</i> Species of roundworm

Toxascaris leonina is a common parasitic roundworm found in dogs, cats, foxes, and related host species. T. leonina is an ascarid nematode, a worldwide distributed helminth parasite which is in a division of eukaryotic parasites that, unlike external parasites such as lice and fleas, live inside their host. The definitive hosts of T. leonina include canids and felines (cats), while the intermediate hosts are usually rodents, such as mice or rats. Infection occurs in the definitive host when the animal eats an infected rodent. While T. leonina can occur in either dogs or cats, it is far more frequent in cats.

<span class="mw-page-title-main">Pinworm infection</span> Medical condition

Pinworm infection, also known as enterobiasis, is a human parasitic disease caused by the pinworm, Enterobius vermicularis. The most common symptom is pruritus ani, or itching in the anal area. The period of time from swallowing eggs to the appearance of new eggs around the anus is 4 to 8 weeks. Some people who are infected do not have symptoms.

<span class="mw-page-title-main">Anthelmintic</span> Antiparasitic drugs that expel parasitic worms (helminths) from the body

Anthelmintics or antihelminthics are a group of antiparasitic drugs that expel parasitic worms (helminths) and other internal parasites from the body by either stunning or killing them and without causing significant damage to the host. They may also be called vermifuges or vermicides. Anthelmintics are used to treat people who are infected by helminths, a condition called helminthiasis. These drugs are also used to treat infected animals, particularly small ruminants such as goats and sheep.

<span class="mw-page-title-main">Soil-transmitted helminthiasis</span> Roundworm infection contracted from contaminated soil

Soil-transmitted helminthiasis is a type of worm infection (helminthiasis) caused by different species of roundworms. It is caused specifically by those worms which are transmitted through soil contaminated with faecal matter and are therefore called soil-transmitted helminths. Three types of soil-transmitted helminthiasis can be distinguished: ascariasis, hookworm infection and whipworm infection. These three types of infection are therefore caused by the large roundworm A. lumbricoides, the hookworms Necator americanus or Ancylostoma duodenale and by the whipworm Trichuris trichiura.

Hookworms are intestinal, blood-feeding, parasitic roundworms that cause types of infection known as helminthiases. Hookworm infection is found in many parts of the world, and is common in areas with poor access to adequate water, sanitation, and hygiene. In humans, infections are caused by two main species of roundworm, belonging to the genera Ancylostoma and Necator. In other animals the main parasites are species of Ancylostoma. Hookworm is closely associated with poverty because it is most often found in impoverished areas, and its symptoms promote poverty through the educational and health effects it has on children. It is the leading cause of anemia and undernutrition in developing countries, while being one of the most commonly occurring diseases among poor people. Hookworm thrives in areas where rainfall is sufficient and keeps the soil from drying out, and where temperatures are higher, making rural, coastal areas prime conditions for the parasite to breed.

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