Intestinal helminths Flashcards
Helminths
Multicellular eukaryotic animals (worms) that possess digestive, circulatory, nervous, excretory, and reproductive systems. Free-living in soil and water, whereas others are parasites of humans and other animals. Diagnosed detection of eggs or larvae (immature forms) in the stool, the adult worms usually aren’t seen. Eggs may have striations (lines), a spine, or an operculum (a hatch by which the larva leaves). They do not usually increase in number in the host, the adult worm typically just lives in the intestine. Disease is resulting from mechanical damage, eating of host tissues, or competing for nutrients. Helminths are the most abundant but neglected classification of parasites
How big are helminths?
They can be anywhere from 1-2 mm to 10 meters
Dioecious reproduction
Male reproductive organs are in one individual, and female reproductive organs are in another. The male will insert into the groove of the female. These organisms can have testes or ovaries and uterine horns. Reproduction occurs only when two adults of the opposite sex are present in the same host.
Monoecious (hermaphroditic) reproduction
One worm has both male and female reproductive organs and may self-fertilize. Only one adult is necessary for reproduction. Two hermaphrodites may copulate and simultaneously fertilize each other.
Trematodes (flukes)
There are 6,000 species, with only 13 infecting humans causing >250,000,000 infection annually. Fluke = old English “floc” flatfish for or flounder. They are flat worms with hooks (oral sucker), dorsoventrally flattened, and all eggs are operculated. Gut or tissue flukes are associated with foodborne infection. Liver flukes may also be found in the liver or gallbladder. These flukes are smaller and have a “leaf-like” structure, and they are not found unless they are surgically removed. Most commonly monoecious (hermaphroditic)
Schistosoma
A more common type of fluke- acquired from contaminated fresh-water exposure (snail intermediate host) burrow through skin into blood = blood flukes. Dioecious, separate male and female. These flukes have a complicated life cycle
Trematodes (flukes) structure
Flat, leaf-shaped worms. They have no anus, and is therefore said to have an incomplete digestive tract. Flukes have ovaries/testes. The ventral sucker enables attachment to host tissues, from which position the fluke can obtain nutrients, and they have an oral sucker that allows them to acquire nutrients. Geographic distribution of flukes is limited by the specific species of snails they require as intermediate hosts.
How are flukes diagnosed?
Eggs are found within the stool, adults usually are not observed. Eggs may also be found in the urine with Schistosoma
How are flukes distributed in the body?
Depends on the geographic location where the infection is acquired.
Cestodes (Tapeworms)
7000 known species, most infect animals, but some are human pathogens. Proglottids originate from the neck region and are immature, mature or gravid (full of eggs). They have midventral genital and uterine pores, bilobed ovaries, and strain specific egg morphology. Some can produce 1,000,000 eggs/day/worm. Mammals are definitive host with copepods or fish as intermediate hosts.
Cestodes (Tapeworms) structure
Ribbon-like, flat, body of segments/proglottid, contains both male and female reproductive systems, sucking groove, scolex allows for worm attachment to intestinal tissue.
Lacks a digestive tract and does not have a mouth. Nutrients are absorbed through the worm’s cuticle (outer “skin”).
How are tapeworms identified?
By the eggs that they produce and the structures found in the proglottid. They are also identified by the structure of the head and neck. The top of the head (scolex) helps with identification, although the adult worm is usually not found
Tapeworm reproduction
Proglottids originate from the neck region and are immature, mature or gravid (full of eggs). The adult worm will continue to make proglottids, and they become mature as they move down the length of the worm. Once they mature, self-fertilization occurs- the testes and ovaries produce a zygote. The ova will develop within the uterine horn. We can visualize the changes in morphology of the proglottid to know when it’s gravid. A gravid proglottid is considered mature and is full of eggs. Worms can produce one million eggs per day.
Nematodes (Roundworms)
There are 20,000 species to date, estimated to be 1,000,000- these worms are found in all habitats. They can infect all vertebrates, including humans. They are unsegmented worms that are uniform in appearance. Thin, long, cylindrical, mm to meter in length. Have a complete digestive tracts with a protective layer called a cuticle. Ascaris is an example. Associated with contaminated food products
Nematodes (Roundworms) structure
These worms have bilateral symmetry (left body=right body). They have a fully functioning digestive tract (mouth opening, tube-like and terminates in anus). Lack a defined head, tapering anterior and posterior of body. There are no body segments or suckers. Few parthenogenic, most reproduce sexually with males (smaller in size). Female worms have a vagina, vulva, tube-like uteri, oviducts and ovaries. Males can fit into a groove where mating will occur- they are not hermaphroditic. Females are usually much larger than the males. A single female releases 1000 eggs/day- they release slightly less ova since females and smaller and don’t have as many proglottids as other species
How are roundworms identified?
Looking at the mouth- are there teeth or plates? Roundworms do not have suckers and will therefore use teeth to attach to the tissue. Eggs are also found in the intestines of the host which is how they are diagnosed
Parts of nematode structure (5)
- Mouth
- Intestinal tract
- Genital pore- where the male binds to the female
- Ovaries
- Anus
Reproductive strategies of nematodes (2)
- Shed eggs into the lumen of the intestine, eliminated with the feces.
- Eggs consumed by the host either in contaminated food or contaminated drinking water.
Nematode reproduction
Some larvae hatch in the soil and actively penetrate the skin of new hosts. Once in the body, they travel a roundabout route to the intestine. For others, eggs are consumed by the host in contaminated food or water. Most are dioecious and develop through four larval stages either within eggs, in intermediate hosts, or in the environment before becoming adults. Adult, sexually mature stages are found only in definitive hosts with copulation of male and female worms leading fertilized egg production.
Intestinal nematodes (hookworms) (3)
Ancylostoma, Necator, Strongyloides
Distribution of Ascaris lumbricoides
It is a roundworm with worldwide distribution. Ascaris is the most common human helminthic infection. It has the highest distribution in tropical and subtropical areas (the ova survive easier in these environments), and is also commonly found in areas with inadequate sanitation. southern areas of Africa and South America are some problematic areas for this infection. Fairly common in the rural areas of the southeastern US
Ascaris lumbricoides infection
Infection may be asymptomatic if the adult worm burden is low. When the burden is higher, abdominal pain or obstruction may occur. However, the intestinal tract is not the only location where infection occurs since the worms can migrate. Hepatobiliary Ascariasis (HPA) is a possible complication, and the organisms may migrate to the lungs. Malnutrition and “failure to thrive” in children with a high worm burden are due to food absorption by the worm. These worms are about 12 inches long
Hepatobiliary Ascariasis (HPA)
Complication of Ascaris lumbricoides infection- Adult worms block the biliary tract, causing hepatic abscess, appendicitis, blockage, secondary infections, or death. Hepatic abscess formation may be the result of these secondary infections, and the infection can progress and cause death. This is most common in children with a large worm burden. Adult worms may detach and wander as a result of inadequate/incomplete drug treatment
Ascaris lumbricoides lung infection
Occurs when the worms migrate to the lungs. Symptoms include cough (produces worms), dyspnea, and hemoptysis. This is important for the worm’s life cycle, as when people swallow after coughing the worm will end up in the intestinal tract and can progress in its life cycle. Loeffler’s syndrome may occur when the worm is in the lung- eosinophilic pneumonitis, resembles asthma in terms of symptoms. Additional eosinophils will be found in the blood or sputum, which indicates this issue
Ascaris lumbricoides structure
About as thick as a pencil and around 12 inches long. Male worms are smaller and not as thick as the females. There is a curve (kind of a cane shape) at the tail end of the worm in males. They are smooth without striations
Ascaris lumbricoides life cycle (6 steps)
- Infectious state is the consumption of fertilized ova, and the ova are then digested in the stomach
- The eggs hatch and invade the intestinal mucosa- once this occurs, they are in the portal circulation and can travel within the body.
- They travel to the lung and spend 10-14 days there until the larvae can mature
- The larvae ascend the alveolar walls into the bronchial tree and into the throat. From there, they are swallowed by the host
- The larvae end up in the intestinal tract and develop into a full adult worm. This occurs 2-3 months after consumption
- An adult in the intestinal tissue will live from one to two years
Infectious state of Ascaris lumbricoides
Fertilized ova are infectious and are consumed by the host. Unfertilized ova may be passed in the stool of an infected person but ARE NOT infectious. These ova are diagnosed in the fecal material
Ova structure of Ascaris lumbricoides
Fertilized - 45 to 60um, cleavage of internal yolk. Has a yellow/brown (bile) color, oval/spherical, thick wall, hyaline shell. Some structures may be able to be observed in the internal sac. Unfertilized- 80-90um length, 40um width. They are difficult to recognize in stool – looks like a vegetable cell
Enterobius vermicularis (pinworm)
Worldwide distribution, most commonly found in school age and preschool children. Found in crowded conditions (especially preschools and daycares), more common in temperate than tropical countries. Most common helminthic infection in the USA, (~40 million infections). Direct life-cycle – spread by fecal-oral route, so it can be transmitted from one infected child to another. The ova are usually observed rather than the adult worms
Enterobius vermicularis symptoms
Mostly asymptomatic, but there can be intense itching in the perianal area, most commonly in children. If there is abdominal pain or other gastrointestinal symptoms, need to examine further for other GI pathogens
Enterobius vermicularis life cycle
- An embryonated egg is consumed and larvae hatches in the small intestine
- Adults develop, males and females will be found in the large intestine, where they mate
- The gravid female migrates out of the anus at night and deposits eggs (oviposit) in the perianal area
- The larvae in the eggs develop and the eggs rupture after 4-6 hours
- There are then worms in the perianal area which migrate back into the intestinal tissue. It is unclear how often this migration occurs
Enterobius vermicularis ova
Collected in the early morning – tape prep. The ova are 30um by 50um and have a thin, smooth, transparent shell. Oval and asymmetrical – have a flattened side. Contains developed larva
Enterobius vermicularis adult worms
Female – 13mm length, 0.5mm width, males are smaller at 2 to 5mm. The worms have a thin flexible outer covering, fin-like expansion at anterior end of the worm, and a long pointed tail
Trichuris trichiura (Whipworm)
A roundworm with worldwide distribution which is the third most common roundworm found in humans. 800 million people are infected worldwide. Increased numbers are found in areas with tropical weather and poor sanitation practices, and among children. Trichiniasis is primarily found in the southern United States due to the tropical temperatures. The ova are consumed from contaminated food or contaminated soil
Trichuris trichiura symptoms
Frequently asymptomatic (low worm burden). Clinical disease is mainly found in children. Symptoms include bloody diarrhea, chronic colitis, Tenesmus (straining to defecate,
long-term leads to rectal prolapse). Heavy worm burden causes chronic malnutrition, anemia, gastrointestinal problems, possible growth retardation or failure to thrive. The worms secrete a pore-forming protein that may play a role in the common symptoms of anemia and diarrhea. Adult worms do not feed directly on blood or other host tissues.
Ova structure of Trichuris trichiura
Each end of the ova contains a plug that can be removed, allowing the larvae to exit. The eggs go through several advanced molting stages. They are barrel shaped and thick shelled
Infectious stage of stage of Trichuris trichiura
An embryonated egg with the larvae inside it, formed as the egg develops. Once the eggs are consumed, they hatch in the small intestine. As this point, the larvae mature and establish themselves as adults. The adults are about 4 cm in length.
Trichuris trichiura adult worm structure
Males 30-45mm, with coiled posterior, females are 35-50mm with straight posterior. Both have a long, whip-like anterior, which they use to burrow into the mucosa, allowing them to implant in the intestine. Adults reside in the large intestine, cecum and appendix of the host- they have a fixed location. It takes 2 months between consumption and an adult female developing and producing ova. One female worm produces between 3 thousand and 20 thousand eggs per day. Life expectancy is one year
Diagnostic stage of Trichuris trichiura
Diagnostic stage is the unembryonated egg found in the stool.
How is Trichuris trichiura identified?
They have a barrel shaped egg with polar plugs at the ends. These eggs are unembryonated when found in the stool.
Ancylostoma duodenale and
Necator americanus
Nematodes and hookworms. Worldwide distribution and are found in moist, warm climates. They are the second most common helminthic infection. Both N. americanus and A. duodenale are found in Africa, Asia and the Americas. Necator americanus predominates in the Americas and Australia, while only A. duodenale is found in the Middle East, North Africa and southern Europe. Life cycles are identical- CAN NOT differentiate species by ova examination, an adult worm needs to be observed attaching to the intestine (do they have teeth or plates). Location may be able to help with identification as well. Adult worms are rarely found in stool samples
Symptoms of Ancylostoma duodenale and
Necator americanus (5)
- Iron deficiency anemia
- Gastrointestinal and nutritional/metabolic symptoms
- “Ground itch’ at site of filariform larvae penetration
- Respiratory symptoms can be observed during pulmonary migration of the larvae.
- Loeffler’s syndrome - eosinophilic pneumonitis
Why do Ancylostoma duodenale and Necator americanus cause iron deficiency anemia?
Due to blood loss at the site of intestinal attachment of the adult worms, especially if heavy burden. Iron deficiency anemia can be considered a “classic symptom” of a heavy worm burden. Can be accompanied by cardiac complications if the burden is very high.
Cutaneous larva migrans
Also called “ground itch”, it’s a rash which occurs at the site of filariform larvae penetration with Ancylostoma duodenale and Necator americanus. However, a canine hookworm may cause this symptom as well.
Ancylostoma duodenale and Necator americanus life cycle (5 steps)
- The host steps on the Filariform larvae, which have the ability to survive in the environment under favorable conditions for 3-4 weeks. The larvae have the ability to penetrate the skin.
- Once they penetrate the skin, the larvae can access blood vessels and enter the circulation. They can be found in the heart and will migrate to the lungs
- The larvae do not mature in the lungs, they will pass through and exit the pulmonary alveoli, going up the bronchial tree into the throat
- The host coughs and swallows, and the larvae ends up in the intestinal tissue. They will then develop into adults
- They will stay in and adhere to the small intestine, where they may cause blood loss. People may be infected for 2 years or longer
Ancylostoma duodenale and
Necator americanus infectious stage
The infectious stage here is a filariform larva, not ova
Ancylostoma duodenale and
Necator americanus diagnostic stage
Ova within fecal material
How are Nematode
Ancylostoma duodenale and
Necator americanus differentiated?
You need to be able to see the adult worms, although adult worms are almost never seen since they are located in the upper intestine. Using a scanning electron micrograph, it can be observed that Ancylostoma duodenale has 4 teeth in its mouth. Necator americanus does not have teeth, it has cutting plates
Ancylostoma duodenale and
Necator americanus ova structure
Females produce 2500-5000 eggs per day, which are found in the fecal material. They are 60um x 40um, oval, thin-shelled, smooth, non-pigmented and transparent
Ancylostoma duodenale and
Necator americanus adult worm structure
Up to 1.5cm length, upper intestine attached to mucosa by biting – “hooks”. Differentiate species by mouth opening- A. duodenale – 2 pairs of teeth, N. americanus – pair of cutting plates
Strongyloides stercoralis
A nematode (hookworm). Has a worldwide distribution and is found in warm, moist climates. Includes tropical and subtropical regions, as well as the temperate southern region of the United States). Also prevalent in rural areas, institutional settings, lower socioeconomic groups, areas with hygiene issues. It is associated with travel or military service abroad. This species is unique in that it has an auto-infective stage, and autoinfection may occur for decades without symptoms
Strongyloides stercoralis symptoms
75% of patients are asymptomatic due to a low worm burden. 25% (mostly children) are symptomatic, with symptoms alternating between diarrhea and constipation, as well as abdominal pain. In children, malnutrition, blockage, loss of appetite, protein malabsorption and abdominal distension may occur. Itching and inflammation at site of filariform larvae penetration – “ground itch” most commonly on feet. Necrotizing bowel may occur with a high worm burden. Pulmonary- Loeffler’s syndrome can occur during pulmonary migration of the filariform larvae
Dermatologic symptoms of Strongyloides stercoralis
Urticarial rashes on buttocks and waist or chronic dermatitis at site of entry. Larva currens occurs when the worm migrates through the skin- there is a red and itchy rash that may occur around the site of migration on the abdomen or thighs. Larva currens only occurs with disseminated infection
Symptoms of disseminated Strongyloides stercoralis infection
Larva currens is a dermatologic symptom of disseminated infection. Others include abdominal pain, distension, shock, pulmonary and neurologic, septicemia, and is potentially fatal. Blood eosinophilia (allergic response) is exhibited during acute and chronic stages, but may be absent with dissemination.
Strongyloides stercoralis life cycle- parasitic phase (4 steps)
- Once in the circulation, the larvae can migrate to different areas
- In the intestine, the female can produce eggs. We not do not find the eggs- the eggs mature quickly into rhabditiform larvae
- Rhabditiform larvae in the large intestine will progress to the filariform larvae, which is infectious and will penetrate the intestinal mucosa. It will get back into the circulation
- The larvae goes into the bloodstream and exits into the lung. The host will cough and the larvae will end up back in the intestine. It will then go through development to become an adult worm which can lay eggs that mature to larvae, and this autoinfection process keeps repeating within the body. In these individuals, larvae may be seen in the sputum
Strongyloides stercoralis diagnostic form
Rhabditiform larvae that is passed in the stool. Ova is not found in the fecal material, we are looking for worms. People may continue autoinfecting for years and will not have symptoms until they have issues with their immune response. With age, the immune response will not be able to control the infection and people may develop symptoms
Strongyloides stercoralis infectious form
Filariform larvae, which is larvae that has hatched and matured. The host comes across it and it burrows through the skin
Strongyloides stercoralis free living life cycle
One of the 2 life cycles for this species. Male and female mate in the environment and produce infectious rhabditiform larvae that is passed in the stool can develop into a free living adult worm, either male or female. The adult worms can produce eggs that will mature into filariform larvae. Hosts come across the filariform larvae that erodes through the skin and enters the circulation. At this point, the parasitic phase will begin
Strongyloides stercoralis adult worm structure
Rhabditiform larva have a short buccal cavity (mouth area). Prominent, oval genital primordium, about 1/3 distance from the tail. Larvae can be present in very low numbers – require repeated sample submission on successive days
Diphyllobothrium latum
Cestode (tapeworm), also known as the giant fish tapeworm. Found in fresh water fish and is transmitted by the consumption of undercooked or improperly stored fish. Locations- Northern Hemisphere (Europe, North America, Asia) and South America (Uruguay and Chile)
Diphyllobothrium latum symptoms
Symptoms vary based upon worm burden and most infections are asymptomatic. 22% of the people infected have symptoms- includes fatigue, weakness, abdominal discomfort, diarrhea, vomiting, and weight loss. If there is attachment in the jejunum, it can lead to Vitamin B12 deficiency with pernicious anemia. Megaloblastic anemia may occur if there is a high worm burden or long-term infection. Parasite mediated disassociation of vitamin B12 intrinsic factor complex with the gut lumen, making the vitamin unavailable for the host. High burden of intestinal obstruction.
Migration of proglottids to the biliary tract can cause cholecystitis or cholangitis.
Long-lasting infection (decades).
Megaloblastic anemia
Occurs due to inhibition of DNA synthesis during RBC production. Characterized by very large red blood cells. In addition to the cells being large, the inner contents of each cell are not completely developed. This malformation causes the bone marrow to produce fewer cells, and sometimes the cells die earlier than the 120-day life expectancy
Pernicious anemia
A version of megaloblastic anemia, but you also have problems due to a lack of vitamin B12
Diphyllobothrium latum life cycle (8 steps)
- The immature worms are passed in the feces, and it takes them 20 days to mature in water
- Form a coracidia, which hatches from the egg and is consumed by a copepod
- Copepods have a stage of further of the parasite, and is then consumed by fish
- When the fish consumes the infected copepod, there is further development of the parasite. The procercoid larvae are released from the crustacean (copepod) and develops into plerocercoid larva within a small fish
- A bigger predator fish then eats the small infected fish. The larvae end up in the fish muscle
- A human ingests raw or undercooked infected fish
- The larvae will further develop into the full adult tapeworm in the small intestine. The scolex of the worm helps with the attachment to the intestinal tissue
- The adults remain in the small intestine and grow to about 10 meters in length and will have around 3 thousand proglottids. From the time of human consumption of the fish to adults in the intestinal tissue is around 6 weeks
Diphyllobothrium latum diagnostic stage
The unembryonated egg that is passed in the feces
Diphyllobothrium latum ova structure
The ova are large and are commonly the diagnostic stage (55 to 75um length, 40 to 55 width). The shell is smooth and contains an operculum (an “escape hatch”). The operculum can open to allow the parasite to leave the egg, and it has an abopercular knob (opposite from the operculum). The knob is used to identify D. latum. The egg does not have “shoulders” meaning that they don’t sit on a ledge. Lack of shoulder helps to differentiate from Paragonimus westermani. We look at the proglottids of the worm to identify it. Immature eggs are expelled from the proglottids. One worm can produce one million eggs per day, and all of the eggs are passed in the fecal material.
Lifespan of Diphyllobothrium latum
The adult lifespan is 25 years on average
Diphyllobothrium latum adult worm structure
The 3 thousand proglottids are called the strobila (proglottids form a chain). It is 3-10 meters in length. The structures of the proglottids and the scolex (anterior portion with hooks or suckers) can be used to identify the worm. The scolex helps the worm to attach. It is rare in the stool since it is attached in the small intestine. The scolex is almond shaped, 2-3 mm in length and 1 mm in width. The worms have 2 deep dorsoventral suction grooves (bothria=pit) with lateral lip-like folds (phyllon=leaves). Proglottides are rare in stool and distinct to organism. Segments are broader then they are long. Contains coiled uterus in form of compact rosette- can count the uterine horns to differentiate species
Taenia solium
A tapeworm/cestode, the number one cause of new seizures in adults. However, not everyone’s infection will develop into neurocysticercosis. It has worldwide distribution but is more prevalent in poorer communities where humans live in close contact with pigs and eat undercooked pork. Most common form of ingestion is consumption of muscle containing an encysted parasite (larvae), undercooking results in infection.
Taenia saginata
A beef tapeworm (cestode)- comes from undercooked beef products. Transmitted when encysted larvae are consumed. There is an active campaign to screen cattle for infection, and grazing cattle should be removed from land contaminated with human sewage. However, it is much less problematic for human health as compared to T. solium. Can be 2-7 meters in length, one thousand proglottids, and 50 thousand eggs are produced per day
Taenia solium symptoms
Asymptomatic to mild abdominal symptoms- vague abdominal discomfort, hunger pains, indigestion, diarrhea or constipation, weight loss, and low grade eosinophilia and increased serum IgE. Passage (active and passive) of proglottids in the stool is the first indication of illness. Appendicitis or cholangitis can result from migrating worms (proglottids). Common to find a single adult worm, 2 to 7 meters, average 2 to 3 years but up to 25 year life span
Taenia asiatica
Asian tapeworm- not seen in the US at all. It closely resembles T. saginata but can be differentiated based on size, and may be considered a subspecies. Associated with fish, so can be identified by history of food consumption
Cysticercosis and neurocysticercosis is caused by which species?
Unlike the egg of Taenia saginata, the egg of Taenia solium can infect the human host, resulting in a condition called cysticercosis. Occurs when the person consumes ova instead of larvae
Cysticercosis
An extraintestinal form of T. solium infection with serious complications. Occurs from consumption of tapeworm eggs, not encysted larvae from undercooked pork. Most of these patients DO NOT have adult worms in their intestine, ova exposure is by fecal oral contamination of food. Cysticerci (cysts) are found in all body tissues – liver, spleen, eyes, brain. May cause no symptoms – tissue dependent. However, the ova have a preference for brain tissue
Neurocysticercosis
Symptoms include seizures, new onset adult epilepsy, and parkinsonian tremors, it can be fatal. Most common parasitic infection of CNS & most common cause of adult-onset epilepsy worldwide.
50 million people are infected worldwide, with 50,000 deaths annually. The CDC estimates 2% of ED visits annually from seizures, 2,300 hospitalization annually. Cyst in brain grow large 50mm, CSF eosinophilia, lymphocytosis. Highest prevalence- Hispanic populations in southern California, New Mexico, and Texas. People immigrating from south America and Mexico have a higher chance of being exposed
Taenia solium life cycle (4 steps)
- The host consumes the undercooked pork product. The pork muscle is degraded in the stomach, degrading the cyst
- The adults mature and live in the small intestine. The scolex contains hooklets and 4 suckers that attach to intestinal tissue
- Adults grow to around 10 m in length and develop gravid proglottids
- The proglottids are released in feces and consumed by a pig, and the cycle continues when the infected pork is consumed
Taenia solium life cycle- Cysticercosis
- The host consumes an embryonated EGG, not larva
- The egg hatches in the small intestine.
- The egg contains a structure called the oncosphere that accesses our blood supply. Penetrates the intestinal tissue and enters our circulation
- Gets into muscle tissue so the oncosphere can form an encysted structure (Cysticerci). However, cysts can form in the muscle, eyes, or brain. At this point, individuals can present with Cysticercosis
Taenia saginata symptoms
Few symptoms are associated with an adult worm in the intestine- commonly a single adult worm is found. Average length is 12 meters, up to 25 meters in length, and average lifespan is 2 to 3 years but up to 25 year life span. Symptoms include obstruction, hunger pains, diarrhea, weight loss, appendicitis, and general discomfort. Proglottids can crawl from the anus, can be the first indication that infection is present. Most cases in the US come from people who have migrated from other areas
Life cycle differences T. asiatica vs T. saginata (4)
- With T. asiatica, Cysticerci develop in liver of pigs, cattle and goats NOT in muscle
- Adults are much smaller- only 300 to 1000 proglottids
- Typically 4 to 8 meters in length- slightly shorter. Average life span is the same (average 2 to 3 years but up to 25 year life span)
- Commonly find multiple worms per infected individual
Taenia asiatica symptoms
Mostly asymptomatic, but symptoms include abdominal pain, nausea, weakness, weight loss, headache, and changes in appetite. Eosinophilia is associated with intestinal inflammation. Does NOT cause cysticercosis
Taenia infectious stage
For all 3 species- the oncosphere contained within an encysted structure in the muscle
Taenia normal life cycle (3 steps)
This is mostly the same for all 3 species
1. The host consumes the encysted oncospheres in the muscle of the infected animal
2. Adults develop within the intestinal tissue (small intestine). The scolex of T. saginata and T. solium differs, but is responsible for attaching to the tissue
3. The cattle/pig consumes fecal material that has the ova or proglottids, allowing for the life cycle to continue within the mammal. Time of consumption to adult tapeworm ova production is 2 months
Taenia species (3)
- Solium
- Saginata
- Asiatica
T. saginata vs T. solium identification
The scolex of T. saginata contains 4 suckers, and the scolex of T. solium contains suckers, hooks, and rostellum- a ring of hooks on top of head. Proglottids of the 2 species and be differentiated by their size and number of uterine horns- T. saginata is bigger. Saginata is referred to as “unarmed” and solium is referred to as “armed” and is better at attaching to the intestinal tissue
Taenia diagnostic stage
Diagnostics is based on the ova, however, you must have the scolex or proglottids of the adult worms to differentiate between solium and saginata
Taenia saginata and Taenia solium ova structure
Can NOT differentiate species- 30 to 35um, round with radial striated edge, internal oncosphere contains 6 refractile hooks. Adult worm scolex and proglottid needed for ID. CAUTION – problematic laboratory contaminant
Taenia saginata and Taenia solium adult worm structure
T. saginata 4-10m, ~1000 to 2000 proglottids, and T. solium 2-4m, 800-1000 proglottids. Gravid proglottids are longer than wide, solium proglottids are shorter. T. solium contains 7-13 lateral uterine branches and
T. saginata contains 12-30 lateral branches.
Fasciolopsis buski
Fluke, trematode- found in Asia and the Indian subcontinent, especially in areas where humans raise pigs and consume freshwater plants. Has large ova and is found in the circulation
Fasciolopsis buski symptoms
Light burden – most commonly asymptomatic. The adult fluke exhibits attachment to intestinal mucosa – duodenum & jejunum. Heavy burden - diarrhea, abdominal pain, fever, ascites, anasarca (wide-spread edema) and intestinal obstruction.
Fasciolopsis buski life cycle (6 steps)
- Unembryonated ova are found in fecal material
- Further develops into an embryonated egg in fresh water
- Miracidia hatch and penetrate snails
- Several different molts/stages of maturity is found in the snail- sporocysts, rediae, cercariae
- The snail will release the free swimming cercariae in fresh water. It further develops into a Metacercariae
- The Metacercariae attached on a water plant is ingested by humans or pigs, causing infection. Can live in the intestine for about a year
Fasciolopsis buski diagnostic stage
Unembryonated ova that are found in fecal material.
Fasciolopsis buski infectious stage
Metacercariae – tailless encysted late larva of a trematode, form is infective for the host.
Fasciolopsis buski ova structure
Diagnosis is made by eggs in feces. They are large, 130-150µm length by 60-90µm width. Ellipsoidal, operculated, smooth shell, and they are unembryonated when passed in feces. Have an operculum, the
abopercular end is roughened or irregular
Fasciolopsis buski adult worm structure
20-75 mm, poorly-developed oral and ventral suckers. Round cephalic end. Seen only from endoscopy or surgery
Heterophyes heterophyes
Trematode, called the minute intestinal fluke. Very small and difficult to find in the intestine. Found in Egypt, the Middle East, and Far East. Primarily in the Nile delta region, Tunisia, Turkey, and Iran
Heterophyes heterophyes symptoms
Infection is called Heterophyiasis. Symptoms- loss of appetite, diarrhea that may contain blood and colicky abdominal pain. There may be inflammation at the site of infection, ulceration, and necrosis, as well as nausea, vomiting. Migration of the eggs to the heart may occur, causing fatal myocardial and valvular damage. Migration to other organs such as heart, brain, lung, spinal cord has also been reported. There may be migration through lymphatics or circulatory system.
Heterophyes heterophyes life cycle (7 steps)
- Embryonated eggs, each with a fully developed miracidium, are passed in the feces
- Snail host ingests eggs, miracidia emerge from eggs and penetrate the snail’s intestine- go through multiple molts at this stage0 sporocysts, rediae, and cercariae
- Cercariae are released from the snail
- Cercariae penetrate of skin of freshwater fish and encyst as metacercaria in the tissue of the fish
- The host becomes infected by ingesting undercooked fish containing metacercaria, which are released from their cyst in the stomach
- Metacercaria excyst in the small intestine
- Mature to adults in the small intestine
Heterophyes heterophyes diagnostic stage
Embryonated eggs, each with a fully developed miracidium, are passed in the feces
Heterophyes heterophyes infectious stage
The host becomes infected by ingesting undercooked fish containing metacercaria
Heterophyes heterophyes ova structure
The ova are 27-35µm by 11-20µm. They are small, oval shaped, convex operculum, rests on visible “shoulders”. Have an abopercular end, a small knob or hook-like protrusion is often visible. Miracidium is visible in the egg. Eggs found in the stool or in duodenal aspirate are diagnostic of the infection. Impossible to differentiate with Clonorchis sinensis, Metagonimus yokogawai
Heterophyes heterophyes adult fluke structure
Adults are 1 to 2mm length-minute flukes. The testes are large and paired, and are situated near a small ovary. Adults contain BOTH ovaries and testes, and are therefore considered hermaphrodites. Surface of the fluke is covered with minute spines. Adults reside in small intestine of the definitive host.
Parts of the Heterophyes heterophyes structure (6)
- oral sucker,
- ventral sucker (close to mid-line)
- intestine (caecum branches),
- vitellaria – chamber receiving yolk-like material, surrounds the ovum
- ovary
- testes.
Metagonimus yokogawai
The smallest liver fluke (1mm in length) to infect humans. Like all trematodes, it requires a snail as an intermediate host. It’s found in the Far East, Siberia, Manchuria, Israel, and Spain, Northern Africa
Metagonimus yokogawai symptoms
VERY similar to H. heterophyes, the worm burden dictates S&S. Symptoms- diarrhea and colicky abdominal pain. Migration of the eggs to the heart and brain – may result in emboli or granuloma formation
Metagonimus yokogawai life cycle (7 steps)
Basically the same thing as Heterophyes heterophyes
1. Embryonated eggs, each with a fully developed miracidium are passed in the feces
2. Small host ingests eggs, miracidia emerge from eggs and penetrate the snail’s intestine. Goes through several molts- sporocysts, rediae, and cercariae
3. Cercariae are released from the snail
4. Cercariae penetrate the skin of freshwater fish and encyst as metacercaria in the tissue of the fish
5. The host becomes infected by ingesting undercooked fish containing metacercaria
6. metacercaria excyst in the small intestine
7. Mature adult is located in the small intestine
Metagonimus yokogawai infectious stage
The host becomes infected by ingesting undercooked fish containing metacercaria
Metagonimus yokogawai diagnostic stage
Embryonated eggs, each with a fully developed miracidium are passed in the feces
Metagonimus yokogawai ova structure
Indistinguishable from H. heterophyes and Clonorchis. Ova are 27-35µm by 11-20µm. Small, oval shaped, convex operculum, rests on visible “shoulders”. Abopercular end, a small knob or hook-like protrusion is often visible. Miracidium is visible in the egg.
Eggs in the stool or in duodenal aspirate are diagnostic for the infection, adult flukes are not seen.
How is Metagonimus yokogawai diagnosis made?
Microscopic ID - eggs in the stool, RARE adult worms
Based upon ID of adult fluke evacuated after anti-helminthic treatment or found at autopsy.
Metagonimus yokogawai adult worm structure
1 to 2.5 mm length, 0.4 to .75 mm width. Position of ventral sucker (away from midline) allows for differentiation from H. heterophyes. – VS – side of midline, close to genital pore. Adults are located in the small intestine of the host.
Hymenolepis nana
Distributed worldwide, known as the dwarf tapeworm (cestode). The ONLY tapeworm that an intermediate host is NOT required. Therefore, passed eggs are immediately infectious when passed in fecal material. They can survive in the environment for up to 2 weeks, so they are very infectious. 50-75 million infections annually. Infection is most common in children and institutionalized populations. This is one of the species that causes Hymenolepiasis
H. diminuta
Distributed worldwide, known as the rat tapeworm. It is a zoonotic infection. Infrequent infection of humans, there are 500 cases annually worldwide. This is one of the species that causes Hymenolepiasis
Hymenolepiasis symptoms
Asymptomatic cases are common with a low burden, but people may still be asymptomatic when their burden is high. Some reports of headache, diarrhea, abdominal pain, irritability when burden is 1000 to 2000 worms (very high burden). May experience low grade eosinophilia. Children with a heavy burden may have diarrhea with mucous. Reports of autoinfection – eggs hatch in the intestine
Hymenolepis nana life cycle (9 steps)
- Embryonated egg is passed in the feces and may survive in the environment for 10-14 days
- Eggs are ingested by insect
- Humans and rodents are infected when they ingest cysticercoid-infected arthropods
- Embryonated eggs are ingested by humans from contaminated food, water, or hands
- Oncosphere hatches, cysticercoid develops in intestinal villus
- Scolex- rostellum and suckers allow for attachment. Once the head attaches, it produces more proglottids- closest to the head is immature, they are mature at the end of the worm
- Adult in ileal portion of the small intestine
- Eggs can be released through the genital atrium of the gravid proglottids. Gravid proglottids are released and can also disintegrate, releasing eggs that are passed in stools
- Autoinfection can occur if eggs remain in the intestine. The eggs then release the hexacanth embryo, which penetrates the intestinal villus, continuing the cycle
Hymenolepis nana infectious and diagnostic stage
Embryonated egg is passed in the feces and may survive in the environment for 10-14 days. This stage is both infectious and diagnostic. Adult worms or proglottids are rarely found in species
Hymenolepis nana lifespan
Very short, only 4-6 weeks
Hymenolepis nana ova structure
The ova are very infectious, laboratory caution is needed. They are 30 to 50um and oval. Thin outer shell with hexacanth (6 hooklets) and pair of polar filaments are diagnostic
Hymenolepis nana adult worm structure
15 to 40mm in length, may be confused with pinworm. Associated with mucous threads, which are not common in stool samples. Small scolex = Protruding rostellum with a row 20-30 hooklets
Hymenolepiasis diminuta life cycle (7 steps)
- Eggs are passed in feces
- Ingested by an arthropod intermediate host
- Oncospheres hatch and penetrate the intestinal wall
- Cysticerci in body cavity of insect are ingested by rodents or humans- transmitted when humans accidentally ingest it
- Scolex contains suckers and helps with attachment
- Adults in small intestine
- Gravid proglottids, they are hermaphrodites and self fertilize. The proglottids will rupture and release the eggs with the fecal material
Hymenolepiasis diminuta infectious stage
Cysticerci in body cavity of insect which are ingested by rodents or humans
Hymenolepiasis diminuta diagnostic stage
Eggs that are passed in the feces. Proglottids degrade in feces, ID by ova only and lack of polar filaments
Hymenolepiasis diminuta ova structure
The ova are not infectious from person to person. They are 70-85uM, round to slightly oval. Striated outer membrane, space between 2 membranes is smooth. Oncosphere – hexacanth (6 hooklets)
Hymenolepiasis diminuta adult worm structure
20 to 60 cm in length, short and wide proglottids with 3 oval testes
