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McGill University
Microbiology and Immun (Sci)
MIMM 413

Lecture 15 Strongyloidiasis Phylum Nematoda Family Strongylidae Class Secernentasida Order Rhabditoria 100 million people worldwide are infected endemic in tropical regionsAlso known as threadwormsStrongyloides stercoralis causes the most mortality in humansRaccoons are a suspected reservoir in the US and Canada S procyonisNatural hosts humans primates dogs catsExperimental hosts incomplete life cycle gerbils Patas monkeys SCID mice th4most important nematode infection in the worldAsymptomatic chronic disease of the GI tract comaDissemination into organs in immunocompromisedTreatment ivermectin thiabendazole albendazole unless comaDiagnosis blood test serologyeosinophil count and stool eggsLarva L1 only seen in the stool of immunocompromised patientsNo reliable test for diagnosis false positives commonUnique life cycle among nematodes freeliving autoinfective and parasitic life cycles3 components of life cycle autoinfective homogonic direct and heterogonic indirectParthenogenetic unfertilized egg develops into a new parasite wo male involvementParasitic adult females in epithelial mucosa and crypts of Lieberkuhn are parthenogeneticFreeliving adult parasites in the soil reproduce sexually only a few eggs are producedL1 is the rhabditiform posterior end and oesophagus separated by prominent bulbLife cycle determined by ALD sensor default pathway is heterogonicThe larva can actively search for a hostL3a is the autoinfective filariform larger than L3i outside filariform migrates to colonTriggers of autoinfection corticosteroids prednisone immunosuppression infections neonates immunocompromised massive or with Th1 pathogens intestinal stasisInfective filariform properties thermotactic attracted to salt CO urocanic acid geotactic 2 Migration L31 penetrates skinlungssmall intestine takes 56 daysL4 2 daysPeriod prepatent PPP L1 found in faeces 1014 days postinfectionSymptoms GI pulmonary and skin eosinophilia abdominal pain heartburn diarrheaELISA using the NIE recombinant antigen more effective than crude antigenNIE Western blot was more specific than the NIE ELISAHigh prevalence of coinfection with HTLV1 in Caribbean and South AmericaHTLV1 leads to dissemination of strongyloidiasis by increasing the number of regulatory T cells which leads to a reduced IL5 responseThe role of IL5 is to reduce eosinophilia and keep the parasite load in check Lecture 16 Trichinellosis One of the most widespread and clinically important nematodes in the worldWorldwide distribution especially developing or tropical countries Puerto Rico and Australia are free of trichinellosisThe parasite disseminates throughout the body causing extensive inflammationUnlike most nematodes Trichinella is not host specificIt is the largest intracellular parasite but the smallest nematode to infect humansLike most nematodes males are smaller than femalesCommon species T nativa endemic in Canada and T spiralis worldwide except CanadaSpecies not infective to humans T papuae and T zimbabwensisMost species are encapsulated form cysts except the two above and T pseudospiralisGastric acidpepsincysts release larvaesmall bowel mucosaadult worms develop and matenew larvae carried by portal system to liver heart lungs and arteriesLarvae can invade all tissues but preferentially target skeletal muscleOnce a larva invades a muscle fibre it turns it into a nurse cellUnlike most nematodes Trichinella life cycle takes 30 hours instead of 34 monthsThe life cycle had 4 molts larval stagesAll Trichinella species are zoonoses because humans do not play a role in the life cycleSylvatic cycle transmission between vector and wild animalsDomestic cycle transmission between vector and nonwild urban or domestic animalsSymptoms abdominal cramping eosinophilia and diarrheaEncystation fibre loses myofilaments nuclei enlarge smooth ER increases mitochondria degenerate collagen secreted by fibroblastsThe cysts calcifies after 18 months but encysted larvae remain alive for yearsCalcified cysts can be detected by Xray encysted larvae in muscle biopsyTrichinellosis isnt usually fatal but acute phase causes significant inflammation in immunocompromised patients who cannot control the infectionImmune response to initial infection T cells B cells and antibodiesReservoirs T nativa polar bear walrus T spiralis pigUnlike other species T spiralis is not resistant to freezing and has a high reproductionThe stichosome is a row of discoid cells stichocytes containing secretory granulesThese granules are both immunogenic and modulate the host gene expressionThey are secreted into the nurse cell and can be used as a diagnostic toolMost invaded muscles eye tongue masticary muscles diaphragm intercostals arms legsLarvae can infect all muscles but nurse cells do not form in heart or CNSLarvae cannot encyst in smooth muscleInvasion of muscle is associated with intense inflammation due to secretion of granulesResistance can be innate fish amphibians genetics mucus nonspecific acquired Th1 infections M tuberculosis Toxoplasma or specific acquired Th1 Th2 IgM IgG and IgE in serum IgA in gut T cells and ADCCFour cardinal features of trichinellosis fever orbital oedema myalgia eosinophiliaOften asymptomatic but heavy infections can lead to fatal myocarditis or encephalitisUnlike most nematodes adult worms eggs or larvae cannot be detected in stool sampleMigrating juveniles cannot be detected either only nurse cells by biopsyDiagnosis is by biopsy serology not very sensitive false negatives or PCR
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