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