3Where is this Parasite Found? Tropical and Sub-tropcial regionsTemperate regionsRural areas, institutional settings, and in lower socioeconomic groupsMostly found in warm moist areas that favor the survival of the juvenile stages
4Geographic Distribution Currently, an estimated million people are infected worldwide in 70 countriesIn the US: Appalachians, especially in eastern Tennessee, Kentucky, and West Virginia.Internationally: Sub-Saharan Africa, South and Southeast Asia, Central America, and South America, and parts of Eastern Europe
5Question #1Name a state that has Strongyloides stercoralis?
7General Things to Know Commonly called a Threadworm The smallest nematode parasites of humansMost Strongyloides and their eggs are found in the soilInfections are initiated when exposed skin contacts contaminated soilAutoinfection commonly occurs allowing infection to persist for decadesMore common in people who suffer from alcholism, who are caucasion, males, or have an occupation that involves soil contactNot likely to be transmitted through water
8Hosts Definitive Intermediate Hosts Humans Dogs Cats Other mammals NoneThere are 38 species of threadworms found in sheep, swine, goat, ox, deer, camel, rabbit, primates, dogs, and cats
9Question #2How many species of Strongyloides are there?
10Egg stage Eggs are about 50 um to 68 um long and 30 um by 34 um wide. Females produce several dozen eggs and release them in to the gut lumen or submucosaNot normally diagnostic because eggs hatch before exiting the human host
11Rhabditiform larvae stage (L1) Non infective stageSize ranges from microns in length and 60 microns in diameterPassed with feces
14Filariform Stage (L3) Reside in the small intestine of the host They are about 650 microns long and 50 microns in lengthHave a long esophagusThis is the infective stage of Strongyloidiasis
15Filariform Stage (cont’d) Have a long non bulbous esophagus of about 2/5 of the length of the bodyFemale filariform larvae are slender and faster moving than the rhabditiform stageMale filariform larvae are not parasitic, only the females areFilariform larvae penetrate the skin by releasing hydrolitic enzymes
16Question #3Name one of the three distinguishable characteristics of rhabditiform larvae from other species of nematodes?
17Question #4What larvae form is the infective stage?
18Free living Females Have a rhabditiform esophagus Females are about 1 mm in length by um wideContain embryonated eggsFemales have a vulva that is about equatorialFemales uteri contains more eggs than most parasitic females
19Free living Males Have a rhabditiform esophagus Males are up to 0.9 mm long and 40um to 50 um wideHave two simple spicules and a gubernaculumTheir pointed tail is a curved ventrad
20Parthenogenetic females Parthenogenetic females reach a length of mm1/3 of the worm is the esophagusInhabit crypts of the small intestinesFemale is stout and has a vulva that is about equatorialVulva is in the posterior third of the bodyThe uteri carries only a few eggs at a time
21Question #5T/F The adult male is found in the definitive host.
23Life CycleAdults lay eggs in the intestines within the definitive hostRhabditiform larvae hatch from the eggs in the intestinesThree possibilities from hereFree living adult worms (Heterogonic)Filariform larvae (Homogenic - Parasitic Generation)Autoinfection
24Free living adult worms (Heterogonic) Rhabditiform larvae will be excreted in the stoolIn this developmental option, the rhabditiform will molt four times and will either become a female or male adult wormThe free-living adults then mate and produce eggsThe rhabditiform larvae then hatch from the eggsThe larvae then can either produce a new generation of adults or become filariform larvae
25Homogenic Life CycleRhaabditiform larvae will be excreted in the stoolThe rhabditiform larvae molt twice and develop into filariform larvaeNo adult stages outside of host with this life cycle
26AutoinfectionIn this, the rhabditiform larvae develop into filariform larvae before they leave the hosts intestinesThe filariform larvae then penetrate the intestinal mucosa or perianal skinThey then follow the life cycle in the host…to be explained next…
27Parasite in the hostNow, the filariform larvae from each cycle enter the circulatory system and travel to the heartThey come out of the pulmonary artery and enter into the lungsPenetrate the alveolar spaces and are carried to the trachea and pharynx, swallowed, and make there way to the small intestinesIn the small intestines they molt twice and become adult female wormsBy parthenogenesis they produce eggs, yielding rhabditiform larvaeThe prepatent period lasts about 1 monthPossible cycles start over againParthenogenesis – growth and development of an embryo without fertilization of a male
28Question #6Name 1 of the 3 cycles that occurs with Strongyloides stercoralis?
29Question #7What larvae stage is excreted in the stool?
30Transmission Through contaminated soil Autoinfection IngestionSkin contactAutoinfectionTransmammary infection (with dogs)Presumably it can occur in humans
31SymptomsMost Strongyloides infections are asymptomatic and can survive decades undiagnosedThe longest documented asymptomatic infection was more than 65 yearsSymptomatic infections typically manifest in gastrointestinal, pulmonary, and dermatologic systemsIn immunocompromised persons, symptomatic infections can be devastating and carry a 60-85% mortality rateAcute InfectionChronic infectionHyperinfectionDisseminated Infection
32Types of Infections Acute Infection Chronic infection Hyperinfection Symptoms occur after a few weeks whether it is a cough, abdominal pain, diarrhea, and/or anorexia.Most likely detection of hundreds of larvaeChronic infectionmanifested by epigastric pain, recurrent hives (urticaria) and transient red lines on the skin that appear and move rapidly (larva currens) and sporadic diarrheaHyperinfectionMost patients that experience this are immunocompromisedMost likely from accelerated autoinfectionLarge number of parasites presentLarge numbers of larvae in stool and/or sputumDisseminated InfectionMigration of larvae to organs beyond the range of the pulmonary autoinfective cycle
33Gastrointestinal Symptoms Bloating, distensionDiffuse abdominal painDiarrhea, typically nonbloodyAnorexia, weight loss, nauseaMalabsorption syndromes may occur in chronic infections
34Question #8T/F It can be transmitted by breast milk
35Dermatologic Symptoms Ground itch - Papulovesicular pruritic rash, usually on the feetCutaneous infection: Dermatitis is produced by migration of the infective juveniles through the skinPetechial/purpuric rash (with disseminated disease)InflammationSlight hemorrhage and swellingLarva currens – Skin lesions, hives, or rash often on the trunk and buttocks (allergic response due to migrating larvae
36Cardiopulmonary Symptoms Wheezing or coughingMild to severe symptoms of pneumonia when worms are present in the lungsHyperinfection syndromemassive proliferation of larval formsPulpatationsAtriofibrillationsChoking sensation
37Diagnosis Examination of feces and duodenal contents Finding rhabdiform or filariform larvae in a fresh stoolIf not in a fresh stool, may be misdiagnosed as hookwormFinding larvae in the sputumCulture techniquesELISAImmunodiagnosis by indirect immunofluorescenceAntigen: whole Strongyloides ratti larvae
38Question #9Name a way the parasite can be diagnosed?
39Culture Technique Fairly new technique Movement of the larval forms can be seenBacterial colonies of normal oral flora are formed along the moving trailPerformed using a chocolate agar sputum culture
40Treatment and Prevention ThiamendazoleKeeps nematode larvae from growing into adult formsCambendazoleIvermection – 100% effective for clearing Strongyloides infection with no side effects
41Control Proper hygiene Do not allow infected hosts to breast feed Do not walk barefoot in soilIn HospitalsMake sure you wear clean masks, gloves, and apronsWash hands frequently
42Question #10What drug is 100% effective against Strongyloidiasis?
43Question #11Are you more likely to get Strongyloidiasis by swimming in a lake or walking barefoot in the woods?
44Works citedSchmidt, G., & Roberts, L. (2005). Foundations of Parasitology (7th ed.). New York, NY: McGraw-HillSchmidt, G.S., and L.S. Roberts Chapter 25. Order Rhabditata: Pioneering Parasites. in Foundations of Parasitology. Times Mirror/Mosby College Publishing. St. Louis pages.