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HUMAN PARASITOLOGY Unit 3.
3.1 Nematodes, the diseases caused by them, their treatment and control
The nematodes or roundworms constitute the phylum Nematoda. They are a diverse animal phylum inhabiting a very broad range of environments. Nematode species can be difficult to distinguish, and although over 25,000 have been described, of which more than half are parasitic, the total number of nematode species has been estimated to be about 1 million. Unlike the phyla Cnidarians and Platyhelminthes (flatworms), nematodes have tubular digestive systems with openings at both ends. Nematodes commonly parasitic on humans include ascarids (Ascaris), filarias, hookworms, pinworms (Enterobius) and whipworms (Trichuris trichiura). The species Trichinella spiralis, commonly known as the 'trichina worm', occurs in rats, pigs, and humans, and is responsible for the disease trichinosis. Baylisascaris usually infests wild animals, but can be deadly to humans, as well. A number of intestinal nematodes cause diseases affecting human beings, including ascariasis, trichuriasis and hookworm disease. Filarial nematodes cause filariasis.
Parasitic roundworms can live on or in humans where they can cause a variety of health problems. Most parasitic roundworm eggs or larvae (immature form) are found in the soil and enter the human body when a person picks them up on the hands and then transfers them to the mouth. The eggs or larvae also can enter the human body directly through the skin.
With the exception of the parasitic roundworm that causes trichinosis, mature adult roundworms eventually end up or live in human intestines and cause infection and disease. In trichinosis, it is the movement of the larvae through the body from the intestines and their encystment (becoming enclosed in a capsule) in muscle tissue that create serious problems.
Parasitic roundworms that infect humans are much more widespread than many of us realize. Diseases caused by these parasites affect not only poverty-stricken individuals in developing or remote areas of the world, but they also can be important health problems for people throughout the world, including in the United States.
As with other parasitic diseases, roundworm infections in the intestines are more common in warm climates than in cooler, temperate areas.
Many parasitic diseases caused by roundworms result from poor personal hygiene. Contributing factors may include Lack of a clean water supply
Inadequate sanitation measures
Crowded living conditions combined with a lack of access to health care and low levels of education
The best solution is to try to prevent these diseases rather than treat or cure them. School-age children are particularly at risk for parasitic roundworm infections. The parasitic roundworms consume nutrients (nourishing materials) from the children, which can contribute to malnutrition and developmental problems
General life cycle of intestinal nematodes:
Humans ingest infective eggs. Hookworm and Strongyloides stercoralis are exceptions. In these, filariform larvae penetrate the skin to gain entry.
Larvae hatch in intestine.
Male and female adults develop in the intestine. With Ascaris lumbricoides, hookworms, and Strongyloides stercoralis larvae penetrate the intestinal mucosa and initiate a heart - lung cycle enroute to the intestinal tract to mature to adults.
Parasitic roundworms can live on or in humans where they can cause a variety of health problems. Most parasitic roundworm eggs or larvae (immature form) are found in the soil and enter the human body when a person picks them up on the hands and then transfers them to the mouth. The eggs or larvae also can enter the human body directly through the skin.
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With the exception of the parasitic roundworm that causes trichinosis, mature adult roundworms eventually end up or live in human intestines and cause infection and disease. In trichinosis, it is the movement of the larvae through the body from the intestines and their encystment (becoming enclosed in a capsule) in muscle tissue that create serious problems.
Parasitic roundworms that infect humans are much more widespread than many of us realize. Diseases caused by these parasites affect not only poverty-stricken individuals in developing or remote areas of the world, but they also can be important health problems for people throughout the world, including in the United States. As with other parasitic diseases, roundworm infections in the intestines are more common in warm climates
than in cooler, temperate areas.
Many parasitic diseases caused by roundworms result from poor personal hygiene. Contributing factors may include
Lack of a clean water supply Inadequate sanitation measures
Crowded living conditions combined with a lack of access to health care and low levels of education The best solution is to try to prevent these diseases rather than treat or cure them.
School-age children are particularly at risk for parasitic roundworm infections. The parasitic roundworms consume nutrients (nourishing materials) from the children, which can contribute to malnutrition and developmental problems
Pinworm Infection
In the United States, pinworm infection, or enterobiasis, is the most common of all parasitic roundworm infections. It primarily affects school-age children. Because pinworm infection is spread mainly by children, it is found most often in family groups, daycare centers, schools, and camp settings.
Cause
Pinworm infection is caused by an intestinal roundworm called Enterobius vermicularis. Pinworms are small, threadlike roundworms found primarily in the colon and rectum. The life cycle of the pinworm—egg, larva (immature stage), and mature worm—takes place inside the human body and requires from three to six weeks to complete. The pinworm is the most common roundworm parasite in temperate climates—even in areas that have to good sanitation practices.
Pinworms enter body when one swallow their eggs. One female pinworm may expel thousands of eggs into the environment. As the eggs are moist and rather resistant to drying, they can infect humans even after being distributed in dust for several days.
The female pinworm deposits her eggs in the area around anus. One can expose self to the infective eggs by scratching the contaminated area. The eggs then attach to fingertips and from there go into mouth. When one swallow, the eggs travel to intestines.
The eggs also may be scattered into the air from bed linen and articles of clothing. They are capable of clinging to surfaces such as bedding, clothing, toys, doorknobs, furniture, and faucets for up to 2 weeks.
Symptoms
In fact, many people have express no symptoms at all. Of those who do, the symptoms are usually mild and barely noticeable. The movement of egg-laden female worms from anus to deposit their eggs will often produce itching around the anus or vagina. This itching may become very intense, interfere with sleep, and make one irritable. Diagnosis
Healthcare provider can diagnose pinworm infection by simply finding the eggs. The most common way to collect the eggs involves swabbing the anal area with the sticky side of a piece of transparent cellophane tape. Healthcare provider will then put the tape on a slide and look for the eggs under a microscope.
3 Treatment
If healthcare provider prescribes medicine for this condition, everyone who lives in house should take it, regardless of whether they have symptoms. Medicines, such as mebendazole or pyrantel pamoate, are the most useful in treating pinworm infection.
To relieve the intense itching that often happens with pinworm infection, healthcare provider may also prescribe a soothing ointment or cream.
Because of the strong probability that children will be re infected outside the home, in a daycare setting for example, major efforts to eliminate the eggs from the home are of little help.
Prevention
Some of the ways that one and children can prevent becoming infected or re infected with pinworms include Bathing after waking up
Washing night clothes and bed sheets often
Washing hands routinely, particularly after using the bathroom or changing diapers Changing underwear every day
Avoiding nail biting
Avoiding scratching the anal area Ascariasis
Ascariasis, or roundworm infection of the intestines, is common throughout the world in both temperate and tropical areas where sanitation and hygiene are poor. In those areas, everyone may be harboring the parasite that causes the infection.
According to the Centers for Disease Control and Prevention (CDC), ascariasis is estimated to affect between 807-1,221 million people in the world. It is most common in children between 3 and 8 years old.
Cause
Ascaris infection is caused by a parasitic roundworm called Ascaris lumbricoides. This worm resembles the common earthworm. Ranging in length from 6 to 13 inches, the female worm may grow to be as thick as a pencil. Up to 100 worms could potentially infect the human body.
Transmission
Almost more than any other parasitic disease, inadequate personal hygiene leads to ascariasis. Human feces found in fields, streets, and yards are a major source of infective eggs in heavily populated areas.
The eggs do not infect humans when first excreted by the roundworm. They usually are transmitted by hand to mouth. The use of human feces as fertilizer also may permit transmission of infective eggs through food that is grown in the soil and eaten without being thoroughly washed. The eggs are resistant to extremes of temperature and humidity.
The eggs need several weeks to develop and become infective. If one swallow infective eggs, they pass into intestines where they hatch into larvae and then begin their journey through body.
Once through intestinal wall, the eggs reach lungs by means of the bloodstream or lymphatic system.
In lungs, they pass through the air sacs, are carried up the bronchial tree with respiratory fluids and into throat. When in throat, one re-swallow them, and they return to the small intestine where they grow, mature, and
mate.
The worms become mature in about 2 months. Symptoms
If one have only a few roundworms in intestines, one might not have symptoms. If one do have symptoms, one may have vague or off-and-on abdominal pain. The first sign of infection may be the presence of a live worm in vomit or
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stool. If the larvae have migrated to lungs, one may have an illness resembling pneumonia with wheezing, cough, and fever. This stage of the disease happens before the intestinal phase by weeks, and the symptoms are difficult for a healthcare provider to diagnose. If one have a heavy infection of the worms, one may have a partial or complete blockage of the small intestine and have the following symptoms:
Severe abdominal pain Vomiting
Restlessness Disturbed sleep
The heavier or greater the worm infection, the more severe symptoms are likely to be. pancreas might become inflamed. Serious infections, especially those causing blockages, can be fatal.
Diagnosis
Once mature female roundworms are in intestines, a healthcare provider can diagnose the infection by finding the eggs (or live worms) in stool.
Lung infection is more difficult to diagnose, but healthcare provider can confirm it by finding evidence of the larvae in lung or stomach fluids.
Treatment
healthcare provider can treat ascariasis with mebendazole, albendazole, or ivermectin, according to the CDC. Hookworm
An estimated 576-740 million people in the world are infected with hookworm. Hookworm was once widespread in the United States, particularly in the southeastern region, but improvements in living conditions have greatly reduced hookworm infections. Hookworm, Ascaris, and whipworm are known as soil-transmitted helminths(parasitic worms). Together, they account for a major burden of disease worldwide.
Hookworms live in the small intestine. Hookworm eggs are passed in the feces of an infected person. If the infected person defecates outside (near bushes, in a garden, or field) of if the feces of an infected person are used as fertilizer, eggs are deposited on soil. They can then mature and hatch, releasing larvae (immature worms). The larvae mature into a form that can penetrate the skin of humans. Hookworm infection is mainly acquired by walking barefoot on contaminated soil. One kind of hookworm can also be transmitted through the ingestion of larvae.
Most people infected with hookworms have no symptoms. Some have gastrointestinal symptoms, especially persons who are infected for the first time. The most serious effects of hookworm infection are blood loss leading to anemia, in addition to protein loss. Hookworm infections are treatable with medication prescribed by health care provider. 3.2 Tissue Nematodes, diseases caused by them, their treatment and control
Trichinosis
Trichinosis is a parasitic roundworm disease. Human cases of trichinosis have been associated with eating raw or undercooked meat, especially homemade sausage that contains pork or horse meat, as well as eating walrus or bear meat. Fewer people get trichinosis today because of legislation prohibiting the feeding of raw-meat garbage to hogs, commercial and home freezing of pork, and the public awareness of the danger of eating raw or undercooked pork products. Although trichinosis is very uncommon in the United States, it is found occasionally in rural areas.
Cause
Trichinosis is caused by the larvae (immature form) of a highly versatile parasitic roundworm, Trichinella spiralis. This parasite can infect virtually every meat-eating mammal. The parasite is especially common in rats and in swine that feed on raw-meat garbage.
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Unlike some of the other parasitic roundworm diseases, trichinosis is not an intestinal infection in the usual sense. Symptoms are caused by the movement of the larvae from the intestines throughout the body, and also by their encystment (becoming enclosed in a capsule) in muscle tissue.
Typically, the life cycle of the parasite follows these steps:
A person or an animal eats contaminated meat containing parasite larvae.
Digestive juices from the stomach dissolve the capsule-like cyst and release the larvae. The larvae then enter the intestine where they mature into worms and mate.
Female worms pass larvae into the bloodstream where they make their way through the capillaries (tiny blood vessels) into the muscle fibers.
The larvae encyst in the muscle fibers, where they can live for a long time. Symptoms
If one are infected with the worms, one might not have or notice any symptoms. Symptoms of larvae in intestines include
Diarrhea
Abdominal cramps Tiredness
A week after one are infected, larvae enter muscle tissue and can cause these symptoms: Muscle aches and pains
High fever
Swelling in eyes and face
Eye infection (conjunctivitis, or pink eye) Rashes
Being infected by a large number of parasites can cause serious problems affecting heart, breathing, and coordination. Except in severe cases, symptoms usually go away within a few months. Mild pain and fatigue, however, may last for many months.
Diagnosis
Healthcare provider may suspect that one have trichinosis based on symptoms. If one have eaten raw or undercooked meat, be sure to tell healthcare provider. One can be diagnosed in the following ways:
A blood test that shows an increase in the number of a type of white blood cells called eosinophils Examination of muscle tissue (biopsy) under a microscope to look for larvae
Treatment
There are several safe and effective prescription drugs available to treat the symptoms of trichinosis. Treatment should begin as soon as possible. Healthcare provider can decide on the most appropriate treatment based upon symptoms, exposure to raw or undercooked meat, and laboratory test results.
Prevention
One can kill the parasites by fully cooking (allowing all parts of the meat to reach at least 170ºF) or freezing meat. One should keep in mind, however, that smoking, pickling, and other methods of processing or preserving meats do not kill these parasites.
6 Whipworm
What is whipworm?
Whipworm (Trichuris trichiura) is an intestinal parasite of humans. The larvae and adult worms live in the intestine of humans and can cause intestinal disease. The name is derived from the worm’s distinctive whip-like shape.
How is whipworm spread?
Whipworms live in the intestine and whipworm eggs are passed in the feces of infected persons. If the infected person defecates outside (near bushes, in a garden, or field), or if the feces of an infected person are used as fertilizer, then eggs are deposited on the soil. They can then mature into a form that is infective. Roundworm infection is caused by ingesting eggs. This can happen when hands or fingers that have contaminated dirt on them are put in the mouth, or by consuming vegetables or fruits that have not been carefully cooked, washed or peeled.
Who is at risk for infection?
Infection occurs worldwide in warm and humid climates where sanitation and hygiene are poor, including in temperate climates during warmer months. Persons in these areas are at risk if soil contaminated with human feces enters their mouths or if they eat vegetables or fruits that have not been carefully washed, peeled or cooked.
What are the signs and symptoms of whipworm?
People with light infections usually have no signs or symptoms. People with heavy infections can experience frequent, painful passage of stool that contains a mixture of mucus, water, and blood. The diarrhea typically has an acrid smell. In severe cases growth retardation can occur. Rectal prolapse can also occur. In children, heavy infection may be associated with growth retardation and impaired cognitive development.
How is whipworm diagnosed?
Health care providers can diagnose whipworm by taking a stool sample. By using a microscope, providers can look for the presence of whipworm eggs.
How can I prevent infection?
Avoid contact with soil that may be contaminated with human feces, including with human fecal matter ("night soil") used to fertilize crops.
Wash hands with soap and warm water before handling food.
Teach children the importance of washing hands to prevent infection.
Wash, peel, or cook all raw vegetables and fruits before eating, particularly those that have been grown in soil that has been fertilized with manure.
Transmission of infection to others can be prevented by not defecating outdoors, and by
Effective sewage disposal systems. What is the treatment for whipworm?
Whipworm infections are generally treated for 1-3 days with medication prescribed by health care provider. The drugs are effective and appear to have few side effects.
What is preventive treatment?
In developing countries, groups at higher risk for soil-transmitted helminth infections (hookworm, Ascaris, and whipworm) are often treated without a prior stool examination. Treating in this way is called preventive treatment (or "preventive chemotherapy"). The high-risk groups identified by the World Health Organization are preschool and school-age children, women of childbearing age (including pregnant women in the 2nd and 3rd trimesters and lactating women) and adults in occupations where there is a high risk of heavy infections. School-age children are often treated through school-health programs and preschool children and pregnant women at visits to health clinics.
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3.3 Arthropods Vector and their classification, Mode of transmission and pathogenesis of diseases caused by Arthropod vectors
Vector-borne diseases are infections transmitted by the bite of infected arthropod species, such as mosquitoes, ticks, triatomine bugs, sandflies, and blackflies. Arthropod vectors are cold-blooded (ectothermic) and thus especially sensitive to climatic factors. Weather influences survival and reproduction rates of vectors, in turn influencing habitat suitability, distribution and abundance; intensity and temporal pattern of vector activity (particularly biting rates) throughout the year; and rates of development, survival and reproduction of pathogens within vectors. However, climate is only one of many factors influencing vector distribution, such as habitat destruction, land use, pesticide application, and host density. Vector-borne diseases are widespread in the world and are the best studied diseases associated with climate change.
Classification
1. Mosquito-borne Diseases
West Nile fever is caused by the West Nile virus, a virus of the family Flaviviridae which is part of the Japanese encephalitis antigenic group. West Nile fever mainly infects birds and infrequently human beings through the bite of an infected Culex mosquito.
Dengue is the most important arboviral human disease, however, mainly due to nearly universal use of piped water the disease has disappeared from Europe. Dengue is frequently introduced into Europe by travelers returning from dengue-endemic countries but no local transmission has been reported since it would also depend on the reintroduction of its principal vector, the mosquito Aedes aegypti (also the yellow fever mosquito) which is adapted to urban environments. However, over the last 15 years another competent vector Ades albopictus (Asian tiger mosquito) has been introduced into Europe and expanded into several countries, raising the possibility of dengue transmission.
Chikungunya fever is caused by a virus of the genus Alphavirus, in the family Togaviridae, which is transmitted to human beings by the bite of infected mosquitoes such as A aegypti, and A albopictus.
Malaria is caused by one of four species of the Plasmodium parasite transmitted by female Anopheles spp mosquitoes. Historically malaria was endemic in Europe, including Scandinavia, but it was eventually eliminated in 1975 through a number of factors related to socioeconomic development. The potential for malaria and other “tropical” diseases to invade southern Europe is commonly cited as an example of the territorial expansion of risk due to climate change (socioeconomic, building codes, land use, treatment, capacity of health-care system, etc). Projections of malaria under future climate change scenarios are limited in Europe.
2. Sand-fly-borne Diseases
Leishmaniasis is a protozoan parasitic infection caused by Leishmania infantum that is transmitted to human beings through the bite of an infected female sand-fly. Temperature influences the biting activity rates of the vector, diapause, and maturation of the protozoan parasite in the vector. Thus, complex climatic and environmental changes (such as land use) will continue to shift the dispersal of leishmaniasis.
3. Tick-borne Diseases
Tick-borne encephalitis (TBE) is caused by an arbovirus of the family Flaviviridae and is transmitted by ticks (predominantly Ixodes ricinus) that act both as vectors and as reservoirs. Similar to other vector-borne diseases, temperature accelerates the ticks’ developmental cycle, egg production, population density, and distribution. This vector expansion is accompanied by infections with TBE virus. There is considerable spatial heterogeneity in the increased incidence of TBE in Europe, despite observed uniform patterns of climate change. Potential causal pathways
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include changing land use patterns; increased density of large hosts for adult ticks (e.g. deer); habitat expansion of rodent hosts; alterations in recreational and occupational human activity (habitat encroachment); public awareness, vaccination coverage, and tourism. These hypotheses can be tested epidemiologically and tackled through public-health action.
Lyme Borreliosis is caused by infection with the bacterial spirochete Borrelia burgdorferi which is transmitted to human beings during the blood feeding of hard ticks of the genus Ixodes. In Europe, the primary vector is I ricinus, also known as deer tick, as well as I persulcatus from Estonia to far eastern Russia. In Europe, Lyme borreliosis is the most common tick-borne disease with at least 85 000 cases yearly, and has an increasing incidence in several European countries such as Finland, Germany, Russia, Scotland, Slovenia and Sweden. Although detection bias could explain part of this trend, a prospective, population-based survey of cases in southern Sweden has serologically confirmed such an increase49 50.
A shift toward milder winter temperatures due to climate change may enable expansion of Lyme borreliosis into higher latitudes and altitudes, but only if all of the vertebrate host species required by tick vectors are equally able to shift their population distribution. In contrast, droughts and severe floods will negatively affect the distribution, at least temporarily. Northern Europe is predicted to experience higher temperature with increased precipitation while Southern Europe will become drier, which will impact tick distribution, alter their seasonal activity and, shift exposure patterns 51.
Crimean-Congo hemorrhagic fever (CCHF) is caused by an RNA virus of the Bunyaviridae family and transmitted by Hyalomma spp ticks from domestic and wild animals. The virus is the most widespread tick-borne arbovirus and is found in the Eastern Mediterranean where there have been a series of outbreaks in Bulgaria in 2002 and 2003, in Albania and in Kosovo in 200152 53 54. Milder weather conditions, favouring tick reproduction may influence CCHF distribution55. For example, an outbreak in Turkey was linked to a milder spring season (a substantial number of days in April with a mean temperature higher than 5°C) in the year before the outbreak. However, other factors such as land use and demographic changes have also been implicated. There have been new records of spotted fever group rickettsioses with new pathogens such as Rickettsia slovaca, R. Helvetica, Rickettsia aeschlimannii and flea-borne rickettsioses (Rickettsia typhi, Rickettsia felis)57 58. However, this emergence is most likely detection bias due to advancements in diagnostic techniques. Since ticks, flees, and lice serve as vectors as well as reservoirs they might contribute to disease amplification under favorable climate change conditions. There has been a geographic expansion of rickettsial diseases throughout Europe 59, and while underlying reasons for this expansion are still unclear, it is possible that wild bird migration could play a part 60.
Human Granulocytic Anaplasmosis is caused by Anaplasma phagocytophilum, a bacterium usually transmitted to humanbeings by I ricinus. In Europe, this disease was known to cause fever in goats, sheep, and cattle until it emerged as a disease in human beings in 1996 61. It has now shifted to new geographical habitats throughout Europe, and migrating birds have been implicated in its expansion 62. Spatial models have been developed to project the geographical distribution under climate change scenarios for North America but not for Europe 63 64.
3.4 Control mechanisms of Arthropod vectors
Based on the vector-borne disease articles reviewed, here it is clear that climate is an important geographic determinant of vectors, but the data do not conclusively demonstrate that recent climatic changes have resulted in increased disease vector-borne disease incidence on a pan-European level. However, the reports indicate that under climate change scenarios of the last decade’s ticks have progressively spread into higher latitudes; they have become more prevalent in many other places and intensified the transmission season. Conversely, the risk for Lyme borreliosis is projected to be reduced in drought and flood-ridden locations. The risk of reintroduction of malaria into certain countries is very low and determined by other variables rather than climate change. Introduction of dengue, West Nile fever, and chikungunya into new regions in Europe is a more immediate consequence of virus importation into competent vector habitats; climate change is one of many factors that influence vector habitat.
