6. Helminth Parasites - I (Nematodes) & II (Cestodes & Trematodes)

List the Cestodes discussed in this lecture

*Cestodes:* ↳ 1. *Diphyllobothrium spp.* ↳ 2. *Taenia spp.* ↳ 3.*Echincoccus spp.*

Describe Strongyloides stercoralis infection clinically

- *Strongyloidiasis*, the name for any of the manifestation of Strongyloides stercoralis infection, is *split 50/50 with respect to symptomaticity* however, when symptoms are present that can be one or more from an array of possibilities: 1. *Ground Itch w/t Larva Currens* - These terms refer to the presence of *pruritis and inflammation to the site of initial invasion* as well as the manifestation of a *red, deep, raised, intermittently appearing, thick, wiggly, band, usually to the trunk, which engenders Urticaria around it*. Both of these manifestations are in fact *Eosinophilia and Histamine trails which indicate the pattern of migration* 2. *Loeffler's Syndrome* - This term refers to the presence of *cough, asthma-like symptoms, and/or pulmonary infiltrates for one-2 days as a result of eosinophilia and histamine release in the lungs secondary to the invasive transmigration of the S. stercocoralis*. It is important to remember that *with S. stercoralis Loeffler's Syndrome is usually an indicator of a non-Autoinfecting case* 3. *Pneumonitis/Asthmatica* - These terms refer to the presence of *intense pulmonary infiltrates* and *asthma-like symptoms for an extended period of time*. It is important to remember that *Pneumonitis is the result of heavy infestation, short or long* while on the other hand *Asthmatica is the result of chronic autoinfection* 4. *Cochin-China Syndrome* - This term refers to the presence of *abdominal pain, nausea, anorexia, and diarrhea as a result of Th2 IgE response in the GI*. It is important to note that this is the *least common manifestation* 5. Disseminated Infection - This term refers to the *widespread infection and destruction of tissues of the body by larval forms*. - It is important to remember that *#3 and #5 are both more likely outcomes if the patient demonstrates HTLV-1 Infection, Hematologic Malignancy, or takes either Corticosteroids or TNF-a Inhibitors*

Describe diagnosis and treatment of infection by Taenia spp.

- *Taeniiasis is diagnosed by microscopic detection of Proglottids or Embryonated Eggs in stool samples* - *Taeniiasis is treated by administration of Praziquantel* - *Cysticercosis is diagnosed by detection of black holes with white dots inside or calcifications on MRI (cysts)* as well as *serum immunoblot (only with multiple lesions)* - *Treatment of Cysticercosis in the absence of Neurocysticercosis is administration of Albendazole + Praziquantel* - *Treatment of Cysticercosis w/t Neurocysticercosis is often nothing, as killing of the cysts will induce inflammation in the brain (sxs) or calcification on their death (seizure foci)*. It is important to note that *use of anticonvulsants and steroids as adjuvants is common if treating Neurocysticercosis with antiparasitics*

Describe Ascaris lumbricoides infection clinically

- Also known as *Ascariasis*, infection by Ascaris lumbicroides is *overwhelmingly asymptomatic (85%)* but, nevertheless, *when symptomatic (15%), it has several possible manifestations*: 1. *Loeffler's Syndrome* - This term refers to the presence of *cough, asthma-like symptoms, and/or pulmonary infiltrates for one-2 days as a result of eosinophilia and histamine release in the lungs secondary to the invasive transmigration of the A. lumbricoides larvae* 2. *Malnutrition* - *Particularly common when the patient is heavily infested*, this condition is manifest is *anemia, weight loss, low energy, malaise, predisposition towards illness, etc* as a result of the fact that worms are consuming ingested nutrients* 3. Intestinal Obstruction - This occurs only in the rarest of cases due to extremely severe infestation being a precondition 4. Biliary Obstruction - This occurs only in the rarest of cases due to extremely severe infestation being a precondition

Describe infection by Diphyllobothria spp. clinically

- Also known as *Diphyllobothriasis*, infection by Diphyllobothria spp. is *usually asymptomatic* though when it does become symptomatic it induces: 1. *N/V/D* 2. *Pernicious Megaloblastic Anemia* 3. *Peripheral Neuropathies* - Pernicious Anemia and Peripheral Neuropathies only arise in the context of heavy infestations due to the fact that *Diphyllobothria spp. secrete factors which dissociate B12 from IF, leading to no uptake in the Ileum; when burden is heavy enough the body gets no B12*

Describe Enterobius vermicularis infection clinically

- Also known as *Enterobiasis*, infection by E. vermicularis is *sometimes asymptomatic (30%)* but more often than not causes symptoms, including: 1. *Pruritis Ani* 2. Colonic Necrosis & Hemorrhage 3. Ectopic Migrations

Describe Trichinella spp. infection clinically

- Also known as *Trichinellosis*, infection by species of Trichinella results *most of the time in symptoms* and these symptoms are ordered into two phases: 1. *Enteral Phase* - This term refers to the period in which larvae and adult forms are present in the Small Intestine. If the patient is symptomatic during this time (often not), they develop *nausea, malaise, anorexia, diarrhea, or constipation* 2. *Parenteral Phase* - This term refers to the period in which larvae are in the circulation and encysting within skeletal muscle. If the patient is symptomatic during this time (almost always is) they develop *high fever, periorbital edema, myalgias, and weakness* - It is important to remember that *while the larvae preference skeletal muscle, they can infect other tissues. Nevertheless, infections of Heart, CNS, skin, or Kidney only occur when the patient is extremely heavily exposed*

Describe diagnosis and treatment of Ascarisiasis

- Ascariasis is diagnosed via *microscopic identification of A. lumbricoides eggs* - Treatment of Ascariasis is *Albendazole* - Of note, *prevention is great sanitation and hygeine*

Describe the Life Cycle of Ascaris lumbricoides

- Ascaris lumbricoides, also known as *Giant Roundworm*, is a parasitic nematode that is *distributed worldwide in all contexts, tropically focused, and infects over 1 billion patients annually*. Ascaris lumbricoides is known to demonstrate *fecal-oral transmission* and also to *have a reservoir in Pigs*. Ascaris lumbricoides undertakes the following complex life cycle: 1.*Transmission* - Ascaris lumbricoides is introduced to the body by *ingestion of an Embryonated Egg which is hardy and capable of passing through the Stomach to the Small Intestine unharmed* 2. *Progression & Invasion* - Once it has reached the Small Intestine *the Embryonated Egg will hatch into Larvae, at which point they will burrow into the circulation from the Intestines, burrow out of the circulation into the airways, and climb to the top of the Trachea where they may be swallowed again*. This long process of invasion is undertaken secondary to the fact that *the various microenvironments encountered have the environmental cues and resources for the larvae to continually develop through its multiple specialized larval forms, terminating on being swallowed as a mature, sexed adult* 3. *Reproduction* - Once the the adult forms are swallowed, they will *migrate to the colon and continue to feed, grow and develop until they are ready to mate, after which the female will release Embryonated Eggs into the lumen to be passed*.

Describe Chlonorchis & Opisthorchis spp.

- Both genera are *distributed throughout China, Southeast Asia, Japan, The Koreas, Mongolia, Russia, The Urals, and the Caucasus and a focus on ecologies where snails, dogs, and fish interact* - These species, also known as *Liver Flukes* and are associated clinically with *inflammation of the Biliary Tract which results in obstruction, jaundice, and, if prolonged, Cholangiocarcinoma (Chronic Inflammation)* - These species are *diagnosed by microscopic detection of eggs in stool* - These species are *treated by Praziquantel* though Albendazole is an alternative

Describe the general features of Cestodes

- Cestodes are helminths, often referred to as *Tapeworms*, which: 1. *Range from 3mm to 20m in size* 2. *Demonstrate a body plan consisting of a Scolex, the Head/Feeding Apparatus, the Neck, which joins the Scolex to the rest of the Body, and the Proglottids, which are repeated units of bodily function which can continually lengthen* 2. *Demonstrate Complex Life Cycles involving Intermediate Hosts, often, snails, fish, or mammals and spanning, egg, free living larval, and adult reproductive forms* 3. *Are Modular Hermaphrodites, meaning that each proglottid contains both male and female reproductive components* 4. *Are usually well tolerated*

Describe diagnosis and treatment of infection by Diphyllobothria spp

- Diphyllobothriasis is diagnosed by *microscopic detection of eggs in stool samples* - Treatment of Diphyllobothriasis is administration of *Praziquantel* - Of note *prevention is cooking fish*

Describe diagnosis and treatment of Enterobiasis

- Enterobiasis is diagnosed by *microscopic detection of eggs via application of scotch tape to the anus of the infected patient and subsequent plating of that tape* - Enterobiasis is *treated by Albendazole*

Describe the Life Cycle of Enterobius vermicularis

- Enterobius vermicularis, *also known as Pinworm* is a parasitic nematode that is *metropolitan in focus, distributed worldwide, and currently infecting more than one billion people*. Enterobius vermicularis is *transmitted fecal/orally*, undergoing the following simple life cycle: 1. *Transmission* - Enterobius vermicularis is introduced to the body by *ingestion of an Embryonated Egg which is hardy and capable of passing through the Stomach to the Small Intestine unharmed* 2. *Transformation* - Once it has reached the Small Intestine *the Embryonated Egg will hatch into Larvae, develop on the lumen contents, and once developed into mature, sexed adults they will migrate to the Colon and Rectum 3. *Reproduction* - Once in the Colon the adult sexed forms of the worms will *continue to feed, grow and develop until they are ready to mate, after which the female will proceed to the Anus, slither out to the Perianal Folds, and lay her Embryonated Eggs there, ready to pass from the body as fomites or into water to be transmitted to another host*. It is important to remember that *the presence of these eggs elicits pruritis that aids in their spread on fingers used to scratch*

Explain the relationship between Filiariases and Wolbachia

- Filiariases, or infections by Wucheria & Onchocerca, have recently been proven to *incite profound inflammation almost entirely as a result of the fact that they contain within them a Rickettsial organism known as Wolbachia* - Further research has demonstrated that *Wucheria and Onchocerca depend on Wolbachia for their growth, development, and survival; thus, administration of Doxycycline, which kills the Wolbachia, also kills the Parasites* - It is for this reason that *Doxycycline is preferred in the treatment of these parasites rather than Ivermictin*

Describe the general features of the Helminths

- Helminths refers to *a group of multicellular parasites, usually worms, which share widely divergent taxonomy but are united by their parasitic activity and the fact that they infect humans* - Helminths *all reproduce sexually, but can be divided into three classes with respect to reproduction*: 1. *Nematodes* - *Separate Sexes* 2. *Cestodes* - *Modular Hermaphrodites* 3. *Trematodes* - *Whole Body Hermaphrodites* - Most important to remember is the fact that *the hallmark of parasite immune response is Eosinophilia & IgE* and furthermore that *immune response reaches equipoise wherein activity controls existing infection, does not eliminate it, but does block new infection; this is believed to be adaptive as many pathologies arise not from the presence of the helminth, but rather from extensive immune activity*

Describe the diagnosis and treatment of Hookworm infection

- Infection by Hookworm is diagnosed by *microscopic detection of Hookworm Eggs on stool sample* and can be *corroborated by mild to moderate anemia* - It is also important to note that *Larva Migrans, a red, superficial cutaneous, wormlike manifestation is also indicative of Hookworm, being the worm's migration in the superficial layers of the skin*. Larva Migrans is considered to be *part of Ground Itch* - Treatment for Hookworm infection is *Albendazole* - Of note, *prevention is achieved by wearing shoes and treating sewage*

Describe infection by Schistosoma spp. clinically

- Infection by Schistosoma species, also known as *Schistosomiasis*, manifests in many different ways, both with respect to species and mechanism: 1. *Swimmer's Itch/Cercarial Dermatitis* - These terms refer to *inflammation of the skin secondary Cercarial penetration of the skin but failure to penetrate the circulation and depart*. This manifestation of Schistosomiasis is *common to all Schistosoma spp.* 2. *S. haematobium* ↳ 2a. *Hematuria* ↳ 2b. *Calcific Scarring of the Bladder* ↳ 2c. *↑↑Risk of SCC of the Bladder* ↳ 2d. *Infertility - Progressive Infection, Scarring, Fistulae, and Extension* 3. *S. mansoni & japonicum* ↳ 3a. *Periportal Fibrosis* ↳ 3b. *Ischemic Stroke* ↳ 3c. *Spinal Cord Ischemia* ↳ 3d. *Katayama Fever* - It is important to note that *Periportal Fibrosis, due to deposition of eggs, will result in Portal HTN which in turn, if high enough for long enough, will result in Splenomegaly and Esophageal Varices* - Katayama Fever refers to *abrupt onset of rash, fever, headache, myalgias , eosinophilia, urticaria, and dyspnea 2-12 weeks s/p exposure which persist for 2-10 weeks* - It is important to note that *all manifestations beyond Swimmer's Itch and hematuria are the result of deposition of eggs at the locale in question and their incitement of granulomatous/fibrotic inflammation (Th2 Response)*

Describe infection by Taenia spp. clinically

- Infection by Taenia species can result in one of two clinical manifestations: 1. *Taeniiasis* - Taeniiasis refers to the *presence of adult Taenia species in the Small Intestine as a result of ingestion of Encysted Eggs/Onchospheres (Transmissive Life Cycle)*. The presence of these adults is marked clinically by *N/V/D, if the patient is symptomatic though most often they are asymptomatic*. 2. *Cysticercosis* - Cysticercosis refers to the *presence of onchospheres in the tissues of the body as a result of ingestion of free Embryonated Eggs and/or Gravid Proglottids (Disease Life Cycle)*. It is important to remember that *patients are asymptomatic until the Onchospheres die (5-25 years), thereby inciting inflammation in the tissues that they have seeded* and also that *the favored tissues are muscle, eye, brain, heart, and subcutaneous*. While the symptoms are specific to the tissues in which inflammation is induced, the most common issue is *Neurocysticercosis, or the development of seizures and behavior changes as a result of inflammation induced by death of cysts in the CNS* - Another way to explain Cysticercosis is that *it results from the fact that Onchospheres can infect the body, due to genetic similarity between us and its preferred hosts, they are only useful for transmission in short lived animals; the long lives of humans effectively run out the clock*

Describe Wucheria bancrofti infection clinically

- Infection by Wucheria bancrofti, also known as *Lymphatic Filiariasis* and results in one of two presentations: 1. *Acute Adenolymphangitis* - This manifestation, which refers to *extreme edema/inflammation to the Lymphatics and Nodes*, occurs secondary to *multiplication and development of adult W. bancrofti and the resulting inflammation and fibrosis which damages the channels*. This disease process can either *resolve after acute presentation* or, more seriously, present as *Elephantiasis, a permanent collection of fluid to a region of the body as a result of destruction of major lymphatics out of that region* 1. *Tropical Pulmonary Eosinophilia* - This term refers to the presence of *cough, pulmonary infiltrates, and fever as a result of eosinophilia and IgE activity in the lungs secondary to infiltration by Microfilariae* - In essence, *with respect to filarial nematodes, distinct diseases result from either the activity of the Adult Form or the dispersion of microfilaria which die and incite inflammation with fibrosis*

Describe infection by Necator americanus or Ancylostoma duodenale

- Infection by either Hookworm is *overwhelmingly asymptomatic (85%)* but, nevertheless, *when symptomatic (15%), it has several possible manifestations*: 1. *Ground Itch w/t Larva Migrans* - This term refers to the presence of *pruritis and inflammation to the site of initial invasion* as well as the manifestation of *red, superficial, worm-like lesions to the skin at the site of inoculation, representing migration of the worm*. Both of these manifestations are the result of *Eosinophilia and Histamine release to the sites of infection and migration* 1. *Loeffler's Syndrome* - This term refers to the presence of *cough, asthma-like symptoms, and/or pulmonary infiltrates for one-2 days as a result of eosinophilia and histamine release in the lungs secondary to the invasive transmigration of the A. lumbricoides larvae* 2. *Abdominal Pain & Anemia* - This presentation refers to the fact that *both worms, but particularly Ancylostoma duodenale, bury their mouths into the mucosa, wherein they consume blood directly, rich as it is in both RBC's and nutrients (iron) necessary to produce them*. It is important to note that *this more often than not occurs in cases where infestation is great*. In addition to anemia, this pathogenesis can *also lead to abdominal pain if extensive enough*

Describe the diagnosis and treatment of Toxocara canis

- Larva Migrans is treated by *Corticosteroids +/- Albendazole (if active)* - Of note, *prevention of Larva Migrans is avoidance of mouth contact with dogs*

Describe the Life Cycle of Necator americanus and Ancylostoma duodenale

- N. americanus and A. duodenale, also known as *Hookworms*, are parasitic nematodes which demonstrate *worldwide distribution to the Tropics and Subtropics with a focus on Southeast Asia and other regions with poor hygeine*. Hookworms are known to demonstrate *transdermal transmission* and undertake the following complex life cycle: 1. *Invasion* - Necator americanus or Ancylostoma duodenale are *introduced to the body by transdermal invasion of the feet to the circulation, whereby they arrive at the Lungs, burrow out of the circulation into the airways, and climb to the top of the Trachea where they may be swallowed to pass into the GI* 2. *Progression* - Once in the Gastrointestinal Tract Hookworms *migrate to Small Intestine, grow and develop into full sexed adults on lumenal contents, mate, and subsequently release Embryonated Eggs* 3. *Development* - Once released into the world by passage of feces, *Embryonated Eggs develop into larval forms in the soil, ready to invade another host*

Describe Onchocerca volvulus infection clinically

- Onchocerca volvulus infection, also known as *Onchocerciasis*, results in the two possible manifestations: 1. *Cutaneous Onchocerciasis* - This term refers to the presence of *subcutaneous proliferative nodules of adult Larva with overlying papular cutaneous inflammation*. This form of growth and resulting inflammation is often joined by depigmentation* 2. *African River Blindness* - This term refers to the *loss of vision due to opacification of the corneas secondary to their seeding with microfilaria, subsequent death, and incitement of inflammation/fibrosis* - In essence, *with respect to filarial nematodes, distinct diseases result from either the activity of the Adult Form or the dispersion of microfilaria which die and incite inflammation with fibrosis*

Describe the Life Cycle of Onchocerca volvulus

- Onchocerca volvulus is a parasitic nematode that demonstrates *distrbution to Africa and transmission by the African Black Fly* - O. volvulus is notable for the fact that *its life cycle is identical to that of W. bancrofti with the exception that it is transmitted by the Black Fly and that it attacks subcutaneous tissue rather than lymphatic channels*

Describe the diagnosis and treatment of Onchocerca volvulus infection

- Onchocerciasis is *diagnosed by microscopic detection of microfilariae on microbiopsies* - Treatment of Onchocerciasis includes *Ivermectin* though Doxycycline is an alternative

Describe the pathogenesis of parasites with respect to risk factors

- One of the most important things to remember about parasites is that *risk factors for parasites usually overlap, meaning that the presence of one helminth or protozoa greatly increases the risk of infection by another* - Because of this possibility *detection of the presence of one parasite should increase suspicion for the presence of others as well*

Describe the prevention of Parasite infections

- Parasite prevention is a *multicomponent process*, relying on the use of all of the following to reduce incidence: 1. *Sanitation/Water Management* 2. *Education of Parasite Risk Factors* 3. *Control of Vectors* 4. *Delivery/Admin of Good Drugs* - As you can imagine, *the efficient and effective execution of all the components involved in the above requires a great deal of political will, manpower, expertise, and raw funds, all of which are in low supply in the countries most affected by these diseases*

Define Parasite

- Parasite refers to any organism that grows, feeds, and is sheltered on or in a different organism while contributing nothing to the survival of its host

Describe Parasitic Disease epidemiologically

- Parasites are *extremely problematic causes of disease across the world, generating a huge economic and health burden for millions of people* - With respect to Malaria, *300-500 million infections occur annually* and of those infections, *450,000 die, with 90% of the deaths being in children under 12* - With respect to intestinal parasites, *up to 2 billion GI tracts are colonized worldwide* with the consequences being that *many patients experience malnutrition which leads to anemia, growth retardation, and impaired cognitive development* - With respect to lymphatic parasites, *up to 110 million are infected currently* and furthermore, *40 million are permanently disabled as a result of infection, making them the second leading cause of disability worldwide* - With respect to parasites of the skin, *up to 25 million are infected*, with the most prominent manifestation being *infection of the eye*. As a result of such eye infection *550,000 people worldwide are blind*

The Eggs of Schistosoma spp.

- Remember that *S. hematobium eggs are found in urine, while the others in feces*

Describe the Life Cycle of the Schistosoma spp.

- Schistosoma species, specifically *mansoni, haematobium, and japonicum* are parasitic trematodes which demonstrate *distribution to the Western USA, Sub-Equatorial Africa, Coastal Eastern South America, the Antilles, the Middle East and SE Asia, with a focus on water sources, as their reservoirs/intermediate hosts are snails*. Schistosoma species demonstrate the following life cycle: 1. *Transmission* - Schistosoma species arrive in the body by *penetration of the skin as Cercariae, free swimming forms released by Snails*, and in turn, *invasion into the circulation as Schistosomulae* 2. *Migration & Progression* - Once inside the circulation, Schistosomulae *proceed to the vessels of the Portal System, where they take residence, consume ingested resources, mature into adults, and pair off to mate hermaphroditically* 3. *Migration & Release* - Once the adults have paired off in the Liver they *migrate to either the Mesenteric Venules to release eggs that penetrate to the GI lumen to be passed in the stool (japonicum & mansoni) or to the Venous Plexus of the Bladder, where they release eggs that penetrate to the Bladder Lumen to be passed in the urine (haematobium)* 4. *Development* - Once released into the environment, *if they are in water they hatch, releasing Miracidia, a form infectious to snails* 5. *Infection & Progression for Transmission* - Once the Miracidia are present in the water they *freely float until they encounter a snail, at which time they penetrate the tissue and generate Sporocysts which eventually develop through successive generations into Cercariae which are released to repeat the cycle*

Describe diagnosis and treatment of infection by Schistosoma spp.

- Schistosomiasis is *diagnosed by microscopic diagnosis of eggs* - Schistosomiasis is *treated by Praziquantel* - Of note, *Schistosomiasis is prevented by sanitation, protection/purification of the water supply, and use of molluscicides*

Describe the Life Cycle of Diphyllobothrium spp.

- Specifically referring to *D. latum & D. pacificum*, Diphyllobothrium spp. are parasitic cestodes which demonstrate *distribution to North America, Northern & Eastern Europe, Russia, Japan, and Chile* as a result of their *living in fish which live in such colder climes*. Diphyllobothrium species are known to be *transmitted as a result of eating undercooked fish* and are able to *grow up to 30 feet in length*. Their complex life cycle is as follows: 1. *Transmission* - Diphyllobothrium spp. arrive in the human body by *ingestion of Plerocercoids, or infective larvae residing in the muscles of infected fish which have not been effectively cooked* 2. *Progression & Release* - Once the Plerocercoids arrive in the GI they are *passed to the Small Intestine where they are released from their encasement and develop into adults, releasing eggs from gravid proglottids as they generate them* 3. *Development* - If the Eggs are released into a water source they *develop over 2 weeks into Goracidia, which are ingested by Copepods, small crustaceans* 4. *Infection for Transmission* - Once the Goracidia are within the Copepods they *develop into Procercoids which infect fish which ingest the Copepods, migrating to their muscles to become Plerocercoids ready to infect other animals* - *Plerocercoid → Eggs → Goracidia → Procercoid → Plerocercoid → Eggs →*

Describe the Life Cycle of Strongyloides stercoralis

- Strongyloides stercoralis, also known as *Threadworm*, is a parasitic nematode which demonstrates a *worldwide distribution to the Tropics and Subtropics* and is of particular note for the fact that it *persists in the SE US*. Strongyloides stercoralis undertakes the following life cycle: 1. *Invasion* - Strongyloides stercoralis is introduced to the body by *transdermal invasion of the feet by Filiariform Larvae to reach the circulation, whereby they arrive at the Lungs, burrow out of the circulation into the airways, and climb to the top of the Trachea where they may be swallowed to pass into the GI* 2. *Progression, Mating, and Release* - Once the S. stercoralis larvae are in the GI they *progress to the Small Intestine, consuming lumenal contents to develop into fully sexed adult which mate and release eggs* 3. *Development* - Once eggs are released by the Adult Female *they deposit in the mucosa, hatch, and migrate to the Lumen as Rhabditiform Larva* 4a. *Autoinfection* - One of two possible outcomes, Autoinfection refers to the *persistence and progression of Rhabditiform Larvae to Filiariform Larvae, thereby gaining the ability to penetrate the intestinal mucosa or perianal skin and restart the cycle from invasion* 4b. *Release* - One of two possible outcome, Release refers to the *release 5a. *Direct Progression to Infection* - One of two possible outcomes once released, Direct Progression to Infection refers to *Rhabditiform Larvae which directly progress to Filiariform Larvae, capable of infecting any nearby host directly* 5b. *Indirect Progression to Infection* - One of two possible outcomes once released, Direct Progression to Infection refers to *Rhabditiform Larvae which develop into Free Living Adult Worms which then mate to produce eggs that hatch to become Rhabditiform Larvae with the possibility of either repeating the cycle or progressing to the Filiariform Larval stage and infecting a new host* - It is important to note that *the likelihood of 4a, Autoinfection, occurring, is greatly increased by simultaneous use of corticosteroids*

Describe diagnosis and treatment of Strongyloidiasis

- Strongyloidiasis is *diagnosed by microscopic detection of S. stercoralis larvae*. It is important to remember that other forms of diagnosis include detection of larval forms in the duodenum (aspirate/scopy) or saliva (sample), as well as by serology - It is important to note that *the condition can be *corroborated by Eosinophilia and Anemia, which are common in these patients* - The drug of choice is *Ivermectin*, though Albendazole is an alternative

Describe the Life Cycle of Taenia spp.

- Taenia spp., specifically *saginata, asiatica, and soleum*, are a collection of Tapeworms which demonstrate *worldwide distribution, but a particularly strong focus on regions with poor sanitation and close living with animals; this is because each of these species has a tropism for specific animals, infecting humans secondarily*. Taenia spp. are notable for the fact that they demonstrate two life cycles, one that is transmissive, and the other which induces disease: A. *Transmissive Life Cycle* 1. *Ingestion* - Taenia species arrive in the body secondary to *ingestion of encysted eggs, or Oncospheres, encased in undercooked animal muscle* 2. *Progression* - Once the Oncospheres have arrived in the GI they *pass to the Small Intestine, where they are freed from their encasement by digestion and then encounter environmental cues which induce them to hatch, anchor to the Small Intestine by their Scolex, and develop into mature adults* 3. *Release* - Once the Adults have sufficiently developed and grown they *release Embryonated Eggs and/or Gravid Proglottids into the lumen, allowing them to be passed into the feces* 4. *Infection for Transmission* - If the feces passed by humans infected in this way is both untreated and available to animals, *Embryonated Eggs and/or Gravid Proglottids are ingested by the animal specific to that species and develop into Onchospheres that burrow into the circulation in order to arrive at Skeletal Muscle and encyst themselves, beginning the cycle anew* B. *Disease Inducing Life Cycle* 1. *Ingestion* - In contrast to the transmissive life cycle, the disease cycle begins with *ingestion of free Embryonated Eggs and/or Gravid Proglottids by way of food stuffs being contaminated with infected human feces* 2. *Progression & Invasion* - Once Embryonated Egg and/or Gravid Proglottids arrive in the GI they are *passed to the Small Intestine where they develop into Onchospheres which burrow into the circulation in order to encyst themselves in the tissues of the body, causing inflammation and therefore disease*

Objectives

- To understand parasitic disease at the level of the parasite, the patient, and the community - To understand the life cycles, diagnosis, treatment, and prevention for each of the major parasites discussed

Describe Toxocara canis infection clinically

- Toxocara canis infection, *also known as Visceral Larva Migrans*, refers to any tissue damage which results from the inflammation incited by the presence of larvae in a given tissue*. The most common sites of presence and thus damage are the: 1. *Lungs* 2. *Heart* 3. *Eyes (Dead Retina)* 4. *Brain* 5. *Muscles* - It is important to note that *the general symptoms are eosinophilia and fever* with the other symptoms being site specific (Elevated LFT's, etc)*

Describe the Life Cycle of Toxocara canis

- Toxocara canis is a parasitic nematode which demonstrates a *worldwide distribution with a focus on metropolitan areas*. Toxocara canis is unique among the nematodes discussed in that *humans are a dead end host, being infected only as a by product of the life cycle's execution in the dog*. The life cycle is as follows: 1. *Dog Transmission* - Dogs will be introduced to Toxocara canis by *ingestion of animal droppings which contain Embryonated Eggs* 2. *Dog Progression* - Once in the Small Intestine of the Dog, *Embryonated Eggs hatch, develop into adults, mate, and release eggs which are passed in the feces* 3. *Human Transmission* - As a result of contact with dog feces or consumption of rabbit which has consumed dog feces, *Embryonated Eggs enter into the GI where they develop into Larvae* 4. *Invasion & Inflammation* - Once in the lumen of the Small Intestine, *T. canis larva burrow into the circulation, and seed the body, but lack systems to home to tissues, resulting in stasis and incitement of inflammations to the tissues where they end up, most often the Lungs, Liver, Muscles, Heart, and Brain*

Describe the general features of Trematodes

- Trematodes, also known as *Flatworms or Flukes*, are helminths which: 1. *Range from 1 to 80mm* 2. *Demonstrate complex life cycles involving Snails as the intermediate host* 3. *Are Whole Body Hermaphrodites, meaning that their body contains 1 male sex organ and one female sex organ*

Describe the Life Cycle of Trichinella spp.

- Trichinella spp. (spiralis, nativa, nelsoni, pseudospiralis) are parasitic nematodes which demonstrate *worldwide distribution (if all species counted as one), with a focus on metropolitan areas and domesticated animals as reservoirs*. Infections by these species are considered to be *rare*. Trichinella undertake the following life cycle: 1. *Interanimal Transmission* - In the wild Trichinella spp. undergo complex exchanges, beginning as an Encysted Larvae in skeletal muscle which skeletal muscle is then ingested by other animals, leading to execution of the Life Cycle in them and thus encystment in their skeletal muscle* 2. *Human Transmission* - Trichinella spp. gain access to the body by being *ingested as an Encysted Larva inside of Skeletal Muscle of an animal which has in turn consumed such cysts*. 3. *Progression and Development* - Once an Encysted Larva has been ingested, *the encasing Skeletal Muscle is degraded in the Small Intestine, releasing the Larva to be exposed to proteases which in turn degrade it, releasing the larva itself*. Once free inside the lumen of the Small Intestine *larvae develop into full sexed adults and mate, thus releasing larvae themselves* 4. *Invasion* - Once present in the Small Intestine, these second generation larvae *burrow across the mucosa, gain entry to the circulation, and thereby arrive at Skeletal Muscle across the body, where they burrow in and encyst*

Describe the diagnosis and treatment of Trichinellosis

- Trichinellosis is diagnosed by *harmony between history, symptoms. eosinophilia, and serology or microscopic detection of cysts on biopsy* - Treatment of Trichinellosis includes *Albendazole + Corticosteroids* - Of note, *prevention is achieved by cooking meat well*

Describe the diagnosis and treatment of Trichuriasis

- Trichuriasis is *diagnosed by microscopic detection of eggs derived from stool samples* - It is important that *low level cases may indicate colonoscopy, at which point whipworms with curled heads anchored in the Mucosa and tails in the lumen ought be visible, especially as infestations become more severe* - Treatment of Trichuriasis is *Albendazole*

Describe Trichuris trichiura infection clinically

- Trichuris trichiura infection, also known as *Trichuriasis* is *most often asymptomatic (80%)* but is nevertheless important to note that it *can be asymptomatic, especially with heavier infestations*. The symptoms are as follows: 1. *Diarrhea (Mild to Severe Infestation)* 2. *Anemia (Mild to Severe Infestation)* 3. *Hematochezia (Rare- Severe Only)* 4. *Rectal Prolapse (Rare- Severe Only)*

Describe the Life Cycle of Trichuris trichiura

- Trichuris trichiura, also known as *Whipworm* is a parasitic nematode that is *metropolitan in focus, distributed to the Tropics, and currently infects more than one billion people*. Trichuris trichiura is *transmitted fecal/orally*, undergoing the following simple life cycle: 1.*Transmission* - Trichuris trichiura is introduced to the body by *ingestion of an Embryonated Egg which is hardy and capable of passing through the Stomach to the Small Intestine unharmed* 2. *Transformation* - Once it has reached the Small Intestine *the Embryonated Egg will hatch into Larvae, develop on the lumen contents, and once developed into mature, sexed adults they will migrate to the Colon and Rectum 3. *Reproduction* - Once in the Colon the adult sexed forms of the worms will *anchor their whorled heads into the mucosa and continue to feed, grow and develop until they are ready to mate, after which the female will release Embryonated Eggs into the lumen to be passed*. It is important to remember that *the most common source of infection is tainted water supply or tainted food irrigated by a tainted water supply*

Describe diagnosis and treatment of Wucheria bancrofti

- Wucheria bancrofti is *diagnosed by detection of microfilaria on blood smear taken at night* though it is important to remember that in this country Serology can be used for TPE and US can be used to detect adults in the lymphatic channels - Treatment for infections by W. bancrofti *Doxycycline or Ivermectin*

Describe the Life Cycle of Wucheria bancrofti

- Wucheria bancrofti is a parasitic nematode which demonstrates *worldwide distributions to the Tropics and subtropics, a focus on mosquito infected regions (vector) and currently infects 120 million people*. W. bancrofti undertakes the following life cycle: 1. *Transmission* - Wucheria bancrofti is introduced to the human body by *mosquito bite, which transports L3 Larvae into the skin* 2. *Progression* - Once inside the skin of the bitten tissue *L3 Larvae gain access to the Lymphatics, where they will progressively develop, growing larger maturing into fully sexed adults, and mating to produce waves and waves of microfiliariae* 3. *Release* - Once microfiliariae are released from their progenitors they *migrate into the circulation and lymph where they can be taken up by mosquitoes during blood meals* 4. *Maturation and Reinfection* - Once microfiliariae are present in the mosquito they *shed their sheaths, penetrate the gut, and develop into L3 Larvae which migrate tot he proboscis for reinfection during blood meals*

Describe diagnosis of parasitic infections

1. *Microscopy* - By and large microscopy continues to be the *gold standard of diagnosis*, focusing in particular on the *identification of the adult and egg/cyst forms of the parasite in samples taken from the host* 2. Serology - Serology is less used in the diagnosis of parasites, as it becomes extremely complicated in endemic areas and cannot be used to discern present from past infections. For these reasons *serology is predominantly only useful in diagnosis when the patient is a returning traveler with no previous exposure history (thus making detection of antibodies an indication of current infection)* 3. Molecular Diagnostics - While the use of Molecular Diagnostics akin to MALDI-TOF and Rapid Antigen Testing is growing, these tests are generally not widely available or affordable, a very important issue given that regions in which infection is most endemic are most impoverished

List the types of organisms most commonly found to be parasites

1. *Protozoan Protists* 2. *Helminths*

List the Nematodes discussed in this lecture

A. *GI Pathology Inducing Nematodes* ↳ 1. *Enterobius vermicularis/Pin* ↳ 2. *Trichuris trichura/Whip* ↳ 3. *Ascaris lumbricodes/Giant Round* ↳ 4.*Necator americanus/Hook* ↳ 5. *Ancylostoma duodenale/Hook* ↳ 6 *Strongyloides stercoralis/Thread* B. *Tissue Pathology Inducing Nematodes ↳ 1. *Trichinella spp.* ↳ 2. Toxocara canis ↳ 3. *Wucheria bancrofti/* ↳ 4. *Onchocerca volvulus* - Of note *W. banchrofti and O. volvulus are Filarial Roundworms*

List the Helminths discussed in this lecture

A. *GI Pathology Inducing Nematodes* ↳ 1. *Enterobius vermicularis/Pin* ↳ 2. *Trichuris trichura/Whip* ↳ 3. *Ascaris lumbricodes/Giant Round* ↳ 4.*Necator americanus/Hook* ↳ 5. *Ancylostoma duodenale/Hook* ↳ 6 *Strongyloides stercoralis/Thread* B. *Tissue Pathology Inducing Nematodes ↳ 1. *Trichinella spp.* ↳ 2. Toxocara canis ↳ 3. *Wucheria bancrofti/* ↳ 4. *Onchocerca volvulus* C. *Cestodes:* ↳ 1. *Diphyllobothrium spp.* ↳ 2. *Taenia solium* ↳ 3. *Taenia saginata* D. *Trematodes* 1. *Schistosoma spp./Blood Flukes* ↳ 1a. *S. japonicum* ↳ 1b. *S. mansoni* ↳ 1c. *S. hematobium* 2. Chlonorchis & Opisthorchis spp.

List the Trematodes discussed in this lecture

D. *Trematodes* ↳ 1. *Schistosoma spp.* ↳ 2. Chlonorchis & Opisthorchis spp.