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most common human helminth infections

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Rabaah Jaafari

on 12 December 2013

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Transcript of most common human helminth infections

Most common human helminth infections

Helminths categorized into three classes
Nematodes, Cestodes, and Trematodes.

Helminths can be classified based upon their living site in humans:
1- Intestinal
2- Blood-borne
3- Other-sites parasites
Worldwide Infection!
Three most common infection worldwide:
First: Ascaris lumbricoides
Second: Hook worms
Third: Trichuris trichiura.
Ascaris lumbricoides
Adult A. lumbricoides is the largest human roundworm, clyndrical with three prominent mouth parts.
The females vary in long between 20- 49 cm and 3-6 mm in diameter, the males are shorter, smaller in diameter, and have a distinctive curved end.

Ascariasis is a worldwide infection but the highest prevalence in tropical and subtropical regions, and areas with inadequate sanitation.
In the United States Ascariasis occurs in rural areas of the southeastern states.
It may cause abdominal pain and intestinal obstruction. Migrating adult worms may cause symptomatic occlusion of the biliary tract or oral expulsion. During the lung phase of larval migration, pulmonary symptoms can occur (cough, dyspnea, hemoptysis, eosinophilic pneumonitis - Loeffler’s syndrome).

1-The fertilized egg is oval to round in shape and 45-75 um long and 35-50 um wide. The egg has a thick outer shell called mammillation, which protects it and explains why it is resistant to heat, bleach and other chemicals.

2-The unfertilized egg is longer and may reach up to 90 um long and obviously has no embryo.
Most common human helminth infections
Helminth in Greek means worm.
They are multicellular invertebrates (eukaryotic organisms). Their bodies are flat, mostly like a tube and show bilateral symmetry.
These worms live in living hosts (parasitic) and use them for protection and nutrition. Some are free-living (non-parasitic) in terrestrial and aquatic environments.
Parasitic helminths might disturb the nutritional absorption in the hosts to cause mal-absorption and eventually cause diseases.

lifecycle of Ascaris lumbricoides
Ascaris lumbricoides infections in humans occur via ingesting a fertilized egg, which then become a larval worm that penetrates the wall of the duodenum to the blood stream and carried to the liver, heart, and then to the pulmonary circulation. This larval worm disrupt into the alveoli free, where it grows and molts. The larva takes around three weeks to be coughed from the respiratory system and swallowed again to enter the small intestine again and mature there to adult worms, male and female. If the fertilization occurs, the female then lays a huge amount of eggs daily (200,000 per day) for a year. But these fertilized eggs only become infectious after two weeks in soil and it can persist there for more than ten years. Because the egg has a lipid layer (the outer shell), it is resistant to most of the chemicals. This defense mechanism can explain why is it the most common parasitic infection in the world.
Fertilized egg A. lumbricoides
A. lumbricoides infertile egg
Adult male and female.
Hookworm is the second most common infection. Human hookworms include the nematode species, (Ancylostoma duodenale and Necator americanus). It is mostly in areas with moist, warm climate. 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 ('ground itch') can occur during penetration by the filariform (L3) larvae, and respiratory symptoms can be observed during pulmonary migration of the larvae.
Males measure approximately 8-12 mm long.
Females measure approximately 10-15 mm long.
Adults of both sexes have a buccal capsule containing sharp teeth.
Eggs of hookworm are identical under microscope, (species cannot be differentiated). The eggs are thin-shelled, colorless and measure 60-75 µm by 35-40 µm.
Eggs of hookworm
Is the third most common roundworm infection worldwide.
The infection occurs when human ingest the embryonated egg in contaminated food, specially unwashed vegetables or fruits that have been fertilized by human feces or in the areas where human defecate onto soil.

of T. trichiura takes the large intestine as its habitat. It is also known as whip-worm, due its unique morphology (looks like a whip with a wide posterior end and a very thin anterior end). The male is smaller 30-45 mm and has a distinctive, coiled tail.
The females measure about 35- 50 mm long and has a bluntly round posterior than the male.
The egg has a very distinctive shape, barrel like morphology. This football like egg is bipolar knobs; has a clear mucoid appearing polar plugs at each end. It measures about 50- 54 µm long and 22- 23 µm wide. It is the diagnostic form and it looks golden brown under the microscope.
Other phyla common infection
Cestodes: taeniasis is caused by Taenia saginata and Taenia solium. Those worms have a distinctive characteristic, consist of passage PROGLOTTIDS ( segments contain both male and female organs).

T. saginata Adult can reach 5 meters, 1,000-2,000 proglottids, & up to 100,000 eggs/ proglottids.
T. solium 2-7 meters, avreage of 1,000 proglottids, & 50,000 eggs/ proglottids.

The tapeworms that cause taeniasis (Taenia saginata, & T. solium) are found worldwide. T. solium is more prevalent in poorer communities where humans live in close contact with pigs and eat undercooked pork.
T.solium & T.saginata
life cycle of Taenia species
Humans are the only definitive hosts for Taenia saginata and T. solium species. Eggs or gravid proglottids are passed with feces; the eggs can survive for days to months in the environment. Cattle (T. saginata) and pigs (T. solium ) become infected by ingesting vegetation contaminated with eggs or gravid proglottids .
Humans become infected by ingesting raw or undercooked infected meat . The cysticerci develops over 2 months into an adult tapeworm, which can survive for years. The adult attach to the small intestine by their scolex and reside in the small intestine.
The egg measures 30-35 micrometers in diameter and are radially-striated. The internal oncosphere contains 6 refractile hooks.

Diphyllobothrium latum
What is diphyllobothriasis?
Freshwater fish infected with Diphyllobothrium sp. larva may be transported to and consumed in areas where active transmission does not occur, resulting in human diphyllobothriasis.

The adults fish-tapeworm can reach more than 10 m in length, more than 3,000 proglottids & up to one million eggs per day per worm, which are passed in the feces. Not only human but also mammals can also serve as definitive hosts for D. latum.

Note it is the largest human tapeworm.
Eggs are oval and range in size 55-75 µm by 40-50 µm.
There is an operculum at one end that can be not clearly visible, and at the opposite (abopercular) end is a small knob that can be barely discernible. The eggs are passed in the stool unembryonated.
Diphyllobothrium latum egg
Adult D. latum
Diphyllobothriasis infection can be a long lasting infection and lasts for decades. This infection is asymptomatic, however, migartion of proglottids can also result in complications such as cholecystistis or cholangitis.

Both egg and proglottid are diagnostic tool in stool.
The lifecycle of D. latum
Schistosomiasis or Bilharzia is cause by blood trematodes. The 3 main species infecting humans are S. haematobium, S. japonicum, and S. mansoni. Other species of schistosomes, which parasitize birds and mammals, can cause cercarial dermatitis in humans.

Adult morphology:
The females size 7 -20 mm; males slightly smaller, deposit eggs in the small venules of the portal and perivesical systems.
In case of S. mansoni and S. japonicum the eggs are moved gradually toward the lumen of the intestine eventually appear in feces, but toward the bladder and ureters in case of S. haematobium. Eggs are then eliminated with urine,
Schistosoma adults
S. mansoni, S. heamatobium, and S. japonicum
Eggs of Schistosoma sp.
Life cycle of Schistosoma sp.
Eggs are eliminated with feces or urine. Under optimal conditions they hatch and release miracidia, which swim and penetrate specific snail intermediate hosts (depend on Sp.) cercariae is then developed & penetrate the skin of the human host. then, they shed their forked tail, becoming schistosomulae . The schistosomulae migrate through several tissues and stages to their residence in the veins.
Adult worms in humans reside in the mesenteric venules in various locations, which at times seem to be specific for each species.
S. japonicum is usally found in the superior mesenteric veins draining the small intestine,, and S. mansoni occurs more often in the superior mesenteric veins draining the large intestine. Both can occupy either location, and they can move between sites.
S. haematobium occurs in the venous plexus of bladder, but it can also be found in the rectal venules.
Three most common Nematodes (roundworms) are Ascaris lumbricoides, Hook worms & Trichuris trichiura.
Pinworm ( E. vermicuralis) is the most common infection in the US.
Cestodes: (tapeworms) Taenia solium is porkworm, T. saginata is beefworm, and Diphyllobothrium latum is fishworm and the largest human tapeworm.
Trematodes (blood flukes) include Schistosoma haematobium, S. mansoni, & S. japonicum.
Eggs of P. westermani ( lung fluke) & D. latum (fish tapeworm).
Realizes the infective & diagnostic stage of each ( egg, larva, or proglottids,...etc).

In university hospital, random stool samples were collected from students of medical technology, three samples had the same "object". When the student were asked if they suffer from any symptoms, one only said nothing but abdominal discomfort and it was tolerable, the other two said nothing at all!
What is your diagnosis based upon the pictures?
Case I
A child came with her parents to clinic because she suffered from a serious abdominal discomfort. The physician ran her stool sample to find A, B, and C objects. What is your diagnosis?
Case II
Egg of T, trichiura
A man went to a vacation to Africa after couple of weeks from his return, he complained of abdominal discomfort with bloody urine. He went to his primary physician, who asked him for a urine sample and found nothing!!
Physician suggested a bladder biopsy and found this.
What is the diagnosis?
Case III
Trichuris trichiura
Life cycle of hookworm
Filariform larva (L3) is 500-600 µm long. No pointed tail and a striated sheath.
Rhabditiform (L1) larva that hatches from egg are 250-300 µm long and approximately 15-20 µm wide.
The infection occurs via larvae L3 penetrates the human skin, carried through blood to heart, lung but resides in small intestine, where it matures and lays eggs.
Thank you
Rabaah Jaafari

This infections more frequent in areas with tropical weather and poor sanitation practices. Also in the southern of the United States.
Infection is worldwide but especially among children & cause gastrointestinal problems such as abdominal pain, diarrhea, rectal prolapse, and possibly growth retardation (in heavy infection).
Taeniasis produces only mild abdominal symptoms. The most striking feature of proglottids. Occasionally, appendicitis or cholangitis can result from migrating proglottids. Taeniasis is caused by
ingestion of undercooked meat.
S. mansoni is found in parts of South America and the Caribbean, Africa, and the Middle East.
S. haematobium in Africa and the Middle East
S. japonicum in the Far East.
Many infections are asymptomatic. Acute schistosomiasis (Katayama's fever) may occur weeks after the initial infection, especially by S. mansoni and S. japonicum. symptoms include fever, cough, abdominal pain, diarrhea, hepatosplenomegaly, and eosinophilia. Some times, central nervous system lesions occur: cerebral granulomatous disease may be caused by S. japonicum eggs in the brain.
Artifact is an apparent structural detail that is caused by the processing of the specimen such as: cloth thread, hair, fibers, air bubbles or cells. It can be confusing!!

Another common roundworm
Enterobius vermicularis
(Pinworm) adult females measures 8 -13 mm, adult male: 2 -5 mm.
The most common symptoms of entrobiasis is an itchy anal region. Secondary bacterial infection due to the irritation and scratching of the anal area can occurs in heavy infection. Patient will complain of teeth grinding, and insomnia due to disturbed sleep, thus because pinworm does its work at night. In females the infection can reach the genital tract as well.
Is the most common infection in the US. Children under 18 are most likely to be infected with pinworm. If a child is infected, the whole family has to be treated.
A patient can also re-infect themselves (auto infection) , or be re-infected by eggs from another person.
Simple diagnosis
what is interesting regarding the pinworm diagnosis is that the techniques are easy to do at home.
Parents of infected child can easily wait until their kid is asleep to examine the perianal area to see those small white color worms hatching out side the anus. The worm lays its eggs at
Another technique is attaching a transparent tape (known as scotche tape technique) to the perianal area to collect as possible as pinworm eggs. This technique has to be done in the
before any washing for 3 consecutive days.
Last one is conducted by taking a sample from under fingernail to be examined under rmicroscope (because patient tend to scratch the area & pick worm eggs).
eggs are elongate-oval and slightly flattened on one side & measure 50-60 µm by 20-30 µm.
Egg of E. vermicularis
T. saginata vs. T. solium
Identification of eggs in stool is useless in sp. differentiation, therefore, proglottids and scolex of adult worm are important to differentiate between beef & pork tapeworm.
Note the 4 large suckers in both worms. Rostellum of T. solium containing two rows of hooks.
T. solium contains 7-13 lateral branches; T. saginata 12-30 lateral branches.
Is a tissue infection after ingestion of T. solium eggs, in another word, when human serves as
ingestion the eggs
pass through the lumen of the intestine into the tissues and migrate preferentially to the brain and muscles, where cysts may form & can persist for years. Cysts eventually cause an inflammatory reaction presenting as painful nodules in the muscles and seizures or even eye damage, when the cysts are located in the brain.
Paragonimus westermani
Paragonimus is a lung fluke (flatworm) that infects humans lung after eating an infected raw or undercooked crab or crayfish. Less common, but more serious complications occur when the parasite travels to the CNS.
Cases has been reported from the Midwest of the US.
Adults of P. westermani are hermaphroditic & measure 7.5 -12 mm by 4-6 mm.
Is an acute infection that include cough, abdominal pain, discomfort, and low-grade fever that may occur within 2 weeks after infection. Symptoms may not exist in light infections. However, in long-term infection, symptoms may be misdiagnosed with bronchitis or tuberculosis because of the coughed up blood in sputum.
paragonimiasis is diagnosed by eggs in sputum & stool (coughed up & swallowed).
P. westermani eggs can be confused with D. latum eggs.
Eggs range from 80-120 µm long by 45-70 µm wide. They are yellow-brown, elongate, with a thick shell, and often asymmetrical with one end slightly flattened. The operculum is clearly visible. The abopercular end is thickened. The passed eggs in sputum or stool are un-embryonated.
Egg of P.westermani
P. westermani lifecycle
In the external environment, the excreted eggs in stool or sputum become embryonated, miracidia hatch and seek the first intermediate host, a snail, and penetrate its soft tissues, where they go through several developmental stages inside the snail. Eventually, many cercariae emerge from the snail to invade the second intermediate host such as a crab or crayfish, where they encyst and become metacercariae ( the infective stage).

when human eat undercooked or pickled crab or crayfish that contain metacercariae. The metacercariae excyst in the duodenum & penetrate through the intestinal wall into the peritoneal cavity, then through the abdominal wall and diaphragm into the lungs.
In lungs they encapsulate themselves and mature into adults.
Eggs of D. latum and P. westermani
Other common trematodes
Eggs in stool of Metagonimus yokogawai and Heterophyes heterophyes are identical, however, sp. differentiation is based on the adult fluke identification.

In addition, Clonorchis sinensis (Chinese or oriental liver fluke), which is endemic in Korea, China, Taiwan, and Vietnam.
Adult of C. sinensis
eggs of C. sinensis
Eggs are small, 27- 35 µm by 11- 20 µm. The eggs are oval shaped with a convex operculum, that rests on visible "shoulders," at the smaller end of the egg. At the opposite (larger, abopercular) end, a small knob or (hooklike) is usually visible. Miracidium is visible inside the egg. (distinctive shape like light-bulb egg).
Similar !!
Unfortunately, eggs of T. teichiura can look similar to eggs of another worm. Capillaria philipinensis eggs are smaller in size (35 to 45 µm X 20-25 µm). They have two inconspicuous polar prominences and a

striated shell.
Size chart
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