Nemathelminthes, Nematodes or Roundworms

The Nematodes or roundworms inhabit a broad range of environments. Most species are free-living, feeding on microorganisms, but many are parasitic. Parasitic worms (helminths) are the cause of soil-transmitted helminthiases.

1. MEDICAL
HELMINTHOLOGY
(NEMATHELMINTHES)
Huda AlislamTalab
B.Sc., M.Sc. Medical Parasitology
University of Medical Sciences and Technology (UMST)

2. Nematodes (round worm)
•Thenematodesarefreeliving(majority)orparasitesofhumans,
plantsoranimals.
•Theyaregenerallylightcream-whitecolored.
•Theirlifecycleincludes:egg,larvaeandadult.

3. The parasitic nematodes are divided into :
Intestinalnematodes:
•Ascarislumbricoides
•Hookworms
•Strongyloidesstercoralis
•Trichuristrichuira
•Enterobiusvermicularis
Tissue nematodes :
•Filarialworms
•Dracunculusmedinensis
•Trichinellaspp

4. Intestinal nematodes

5. Ascarislumbricoides
•Ascarislumbricoides,alsoknownasthe
largeintestinalroundworm
•Causeascariasis
•Liveinthesmallintestinefeedingonthegut
contents

6. Transmission
•A.lumbricoidesisspreadbyfaecalpollutionofthesoil.
•Apersonbecomesinfectedbyingestioninfectiveeggsin
contaminatedfoodorfromhandsthathavebecomefaecally
contaminated.

7. Ascarsiasis
•Duringtheirmigration,Ascarislarvaecancauseinflammatoryand
hypersensitivereactionsincludingpneumonia-likesymptoms(Loeffler’s
syndrome).
•Developingandmaturewormsintheintestinefrequentlycause
abdominalpain,nausea,diarrhoeaandvomiting.
•Ascariswormsarelargeandinheavyinfections,especiallyinchildren,
wormcancauseobstructionorperforationoftheintestineand
occasionallyobstructionofthebileductandpancreaticduct.

9. A.lumbricoidesexpelled through anus or mouth
Wormscanpassthoughtheanusorbevomited.

10. Visceral larva migrans
Thisisakindofviscerallarvamigranscausedby
•Toxocaracanis(DogAscaris)(dogroundworm)
•Toxocaracatis(CatAscaris)(catroundworm)
ThelifecycleoftheseparasitesinhostsissimilartothatofA.
lumbricoidesinhumans

11. S. stercoralis
•Thewormisovoviviparous.
•Malesarenotseeninhumaninfectionbecausetheydonothave
penetratingpower,thereforedonotinvadetheintestinalwall.
•Parthenogenesisisaformofasexualreproductioninwhichgrowth
anddevelopmentofembryosoccurwithoutfertilization.
•Theindividualwormhasalifespanof3or4months,butbecauseit
cancauseautoinfection,theinfectionmaypersistforyears.

12. Transmission
•Penetrationofskinbythelarva,whenapersonwalksbarefoot.
•Autoinfection:Itmayleadtoveryheavyinfectioncausingseriousand
sometimesevenfatalillness

13. •Strongyloidosisisgenerallybenignandasymptomatic.
•Bloodeosinophiliaandlarvaeinstoolbeingtheonlyindicationsof
infection.
•Sometimesitmaycauseclinicalmanifestations,whichmaybesevere
andevenfatal,particularlyinthosewithdefectiveimmuneresponse.
•Theclinicaldiseasemayhavecutaneous,pulmonary,andintestinal
manifestations.

14. Hyperinfection
•Inindividualswithcellularimmunedefects,extensiveinternalreinfection
takesplace,leadingtoanmassivenumberofadultwormsintheintestines
andlungsandlarvaeinvarioustissuesandorgans,thisisknownas
hyperinfection.
•Duringhyperinfection,thelarvaemayenterintoarterialcirculationand
lodgeinvariousorganse.g.heart,lungs,brain,kidney,pancreas,liver,and
lymphnodes.
•Manifestationsdependonthesitesaffected.

15. Hookworm
Necatoramericanus
Ancylostomaduodenale

16. •ThebuccalcapsuleofN.americanus
containsapairofcuttingplates,
whereasthatofA.duodenaleconsists
ofactualteeth

17. Transmission
•Humanscontracthookwormwhenfilariformlarvaepenetratethrough
theskin,particularlyintoareassuchasunprotectedfeet.
•Thecommonsitesofentryaretheskinbetweenthetoes,thedorsumof
thefoot,andthemedialaspectofthesole.Infarmworkersandminers,
thelarvaemaypenetratetheskinofthehands.

18. Clinical Symptoms
Hookwormdisease,Ancylostomiasis,Necatoriasis
Therearefourphasesofclinicalmanifestation:
Cutaneous,pulmonary,intestinalandanaemia
•Patientswhoareinfectedmaydevelopintenseallergicitchingatthesite
ofhookwormpenetration,aconditionknownasgrounditch.

19. •Anumberofsymptomsexperiencedbyinfectedpersonsareassociatedwith
larvaemigrationintothelungs,includingsorethroat,bloodysputum,
wheezing,headache,andmildpneumoniawithcough.
•Thesymptomsassociatedwiththeintestinalphaseofhookwormdisease
dependonthenumberofwormspresent.
•Furthermorebecauseadulthookwormscompetewiththehumanhostfor
nutrientsastheyfeed,infectedpatientsmaydevelopamicrocytic
hypochromicirondeficiency,weakness,andhypoproteinemia.
•Mortalitymayresultfromtheenormouslossofblood.

20. •Wormsliveinthesmallintestinebyattachingtothemucoseviathe
buccalcapsule.
•Wormsfeedonhostmucosaandblood
•Wormschangepositionofattachmentsiteevery4–6hoursinresponseto
tissuedepletionandortheonsetoflocalinflammation.
(Thebloodisstillcomingoutfromtheoldattachmentsiteforseveralday)
•Thewormssecreteananticoagulantthatblockstheactionofhosttissue
factorXandVII.Bloodlosscontinuesafterthewormsmovetoanew
location.

21. Cutaneouslarva migrans
(Creeping eruption)
•Variousanimalsharborhookworms.Two
speciesofdogsandcatsareimportant:
•Ancylostomabraziliens:catshookworms.
•Ancylostomacaninum:dogshookworms.

22. •Ifmancomesincontactwithinfectivelarvae,penetrationoftheskinmay
takeplace;butthelarvaearethenunabletocompletetheirmigratory
cycle.
•Trappedlarvaemaysurviveforweeksorevenmonths,migratingthrough
thesubcutaneoustissues.Theymayevokeseverereactionanddermatitis
leadstoscratchingandthenbacterialsuperinfection.

23. Trichuristrichiura
•Causestrichuriasis,whipworminfection.
•Femaleslayingfewthousand(2000-10,000)eggs/day
•Theadultwormsarefoundattachedtothewallofthe
caecumandappendix.

24. As is usual among the nematodes, the females
are larger than the males.

25. Transmission
•Infectionisbyingestinginfectiveeggsincontaminatedfoodorfrom
contaminatedfingers.
•Childrenaremoreofteninfectedthanadults,duetoplayingonfaecally
contaminatedground.

26. Pathogenesis and Clinical
Features
•Duringtheearlystageofinfectiontheremaybeonlylimitedsignsof
infectioninfecalsamples.
•InfectionwithT.trichiura(trichuriasis.whipworminfection)is
asymptomaticexceptwhenthewormloadisheavy.
•Diseasemayresulteitherduetomechanicaleffects(Mechanicaldamage
tothemucosa)orallergicreaction(allergicresponsebythehost).
•Thewormsliethreadedintothecaecalmucosaandeventhoughitisnota
bloodfeeder,oozingofbloodmayoccuratthesitesofattachment

27. •T.trichiurainfectionandaredefinitelyrelatedtothewormburden,the
lengthoftheinfection,andtheageandoverallhealthstatusofthehost.
•Inheavyinfection,thewormmaybeabundantonthecolonicmucosa,
evenuptotherectum.

28. •Mucusdiarrheaandchronicdysenteryarefrequentlyseen.
•Somepatientsmaydeveloprectalprolapse.
•Inthiscaseadultwormsmaybevisibleonmacroscopicexaminationof
therectum.
•Prolapseoftherectumisusuallyseeninpatientswithheavyinfections

29. Enterobuis vermicularis
Pin worm
•ThenameEnterobiusvermicularismeansatinywormlivinginthe
intestine(Greekenteron:intestine,bios:lifeandvermiculus:small
worm)
•ItsoriginalnamewasOxyurisvermicularis,ThetermOxyurismeans
‘sharptail’.

30. •E. vermicularisis a small white worm.
•Also known as the pinworm or threadworm
•Infection is common in children
•A single worm lays from 5000 to 17,000 eggs /day

31. Transmission
•Ingestinginfectiveeggs..
•Autoinfection:byswallowinginfectiveeggsiscommonin
childrensoitthemostprevalenttypeofhumanworm
infection.

32. •Retroinfection:larvaehatchfromtheeggsontheperianalskinand
migratebackintotheintestinewheretheygrowintomatureworms
•Airbornetransmission

33. Enterobiasis(Pinworminfection)
•E.vermicularisinfectionrarelycausesserioussymptoms.
•Thereisusuallyintenseirritationaroundtheanus.(pruritus)
•Wormsintheappendixcancauseappendicitis(Obstructionof
appendixlumenbylargenumberofworms).
•Vulvovaginitis

34. •Themostcommonsymptomsexperiencedbyindividualsinfectedwith
pinwormincludeintenseitchingandinflammationoftheanaland/or
vaginalareas.
•Thesesymptomsmaybeaccompaniedbyintestinalirritation,mild
nauseaorvomiting,irritability,anddifficultysleeping.

35. Tissue nematodes

36. Thisgroupincludes:
•Thefilarialworms
•Theguineaworm(Dranculuculusmedinensis)
•Trichinellaspiralis.

37. The filarial worms
•Thefilarialwormshavecomplexlifecyclesinvolvingadevelopmental
stageinaninsectvector.
•Theyrequireanarthropodvectorfortheirtransmission
•Thewormsinhabiteitherthelymphaticsystemorthesubcutaneous
tissuesofman.
•Humansgetinfectedwhenbittenbytheinfectedarthropodintermediate
host.

38. •Wuchereriabancrofti:Lymphaticfilariasis.
•Brugiamalayi,andBrugiatimori:lymphaticfilariasis.
•Onchocercavolvulus:onchocerciasisorriverblindness.
•Loaloa:Calabarswelling

39. Wuchereriabancrofti
•Wuchereriabancrofticauseslymphaticfilariasis(bancroftianfilariasis).
•W.bancroftiistransmittedbyspeciesofmosquitoesbelongingtothe
generaCulex,AnophelesandAedes.

40. Adult worm
•Adultwormsarelocatedinthe
lymphaticvesselsandlymphnodes
•Theyarelong,slender,creamywhite
threadlike

41. Lymphatic filariasis
•Clinicalfeaturesandpathologydependonthesitesoccupiedbydeveloping
andmatureworms,thenumberofwormspresent,lengthofinfection,and
theimmuneresponsesofthehosttodamagedanddeadworms.
•Lymphaticfilariasisischaracterizedbyrecurrentattacksoffeverwith
painfulinflamedlymphatics.
•Damagetothelymphaticsleadstothickningandeventualblockageof
lymphaticsvessels.

42. •Thelymphaticsinvolvedaremainlythoseofthelimbs,genitalorgansand
breasts.
•Obstructiontotheflowofthelymphcausesswelling,fibrosisand
elephantiasis.

43. Acutelymphaticfilariasis
•Intheacuteformtherearerecurrentattacksoffever(filarialfever)with
painfulinflammationofthelymphnodes(lymphadenitis)andlymph
ducts(lymphangitis).
Chroniclymphaticfilariasis
Ischaracterizedby:
•Hydrocele(isafluid-filledsackinthescrotum)
•Lymphedema
•Elephantiasis
•Chyluria

45. Elephantiasis
•Elephantiasisisacomplicationofadvancedlymphaticfilariasis.Itis
seenasacoarsethickening,hardening,andcrackingoftheskin
overlyingenlargedfibrosedtissues.
•Presenceoftheadultwormscauseslymphaticblockage.
•Theblockagecouldbeduetomechanicalfactorsorallergic
inflammatoryreactiontowormantigensandsecretions.

46. Chyluria
Anuncommoncomplicationofchronicbancroftianfilariasisischyluria.
Itoccurswhentheurogenitallymphaticvesselswhicharelinkedtothose
thattransportchylefromtheintestinebecomeblockedandrupture.

47. Loa loa
Commonname:theAfricaneyeworm.
Loaloacausesloiasiswhichissubcutaneousfilariasis.
Thediseaseisalsoknownas‘Calabarswelling’or
‘fugitiveswellings’
L.loaisoftenreferredtoasthe‘eyeworm’because
theadultwormssometimesmigrateacrossthe
conjunctivaoreyelid.

48. Microfilariaappearinperipheralcirculationonlyduringthedayfrom12
noonto2pm(diurnalperiodicity).
Peakoccursaboutmidday;theremainderofthetimetheycanbefound
inpulmonarycapillaries.
Transmission
L.loaistransmittedbyblood-suckingchrysopsorhorsefliesormango
fliesordeerflies

49. Loiasis
Thepathogenesisofloiasisdependsonthemigratory
habitoftheadultworm.
•Theirwanderingsthroughsubcutaneoustissuessetup
temporaryfociofinflammation,whichappearas
swellingsupto3cminsize,usuallyseenonthe
extremities.
•Thesearethecalabarswellingsorfugitiveswellings,
becausetheydisappearinafewdays,onlytoreappear
elsewhere.

50. •Adultwormsalsomigrateinsubconjunctivaltissues.Theycanbeseen
undertheeyelidsandslowlycrossingthewhiteoftheeye.
•Theycancauseinflammationandirritationbutnotblindness.

51. Dracunculusmedinensis
(Guinea Worm)
•Dracunculusmedinensisisatissue
nematodethatcausesdracunculiasis
(Guineawormulcerdisease).

52. •D.medinensisistransmittedbyswallowingwatercontaininginfected
crustaceanswiththelarvaeofD.medinensisbelongingtothegenus
Cyclops.

53. •D.medinensisisfoundinareaswherecommunitiesuseshallowpondsor
walkinopenwellsassourceofdrinkingwater

54. •Dracontiasisoftencausesseriousclinicalsymptomsespeciallyinheavy
infection.
•Thefemalewormscauseseverepainandallergicreactionincluding
urticaria,fever,nausea,andvomiting.
•Damagetothewormsintheskincanproducesevereinflammation.

55. •Secondaryinfectionmayalsooccurleadingtosepticaemia.
•Ifajointisinvolved,arthritismaydevelop

58. Water filter to prevent infection by
Guinea worm

59. Onchocercavolvulus
•Onchocercavolvulusisasubcutaneousfilarialwormthatcauses
onchocerciasis.
•Thediseaseisalsoknownasriverblindnessbecauseinvasionoftheeye
canleadtolossofvision.
•Onchocerciasis,isamajorpublichealthproblembecausetheinfectionis
aleadingcauseofblindnessintheworldandmayalsocausesignificant
disfigurementoftheskin.

60. •O.volvulusistransmittedbySimuliumblackflies
•Theinfectivelarvaeenterthroughthebitewoundafteraninfected
blackflytakesabloodmeal.

61. Onchocerciasis
•Pathogenesisdependsonthehost’sallergicandinflammatoryreactionsto
theadultwormandmicrofilariae.
•Theseriousclinicalfeaturesandpathologyofonchocerciasisarecaused
mainlybytheinflammatoryreactionsarounddamagedanddead
microfilariae.
•Theinfectivelarvaedepositedintheskinbythebiteofthevector
developatthesitetoadultworms.Adultwormsareseensingly,in
pairs,orintangledmassesinsubcutaneoustissues.

62. Nodule formation
•Themainclinicalfeaturesaretheformationofnodules
(Onchocercomas).

63. •Inflammatorydermatitiswhichisusuallyaccompaniedbyintenseirritation,
raisedpapulesontheskin,andsubsequentlyalterationinthepigmentation
oftheskin.

64. Leopard skin

65. •Theterm‘sowda’(blackdisease)isusedtodescribeasevereallergic
responsewithdarkeningoftheskin.

66. •Inchroniconchocerciasis,theskinlosesitselasticityand
becomeswrinkledwhichmakespeoplelookmoreagedthan
theyare(knownas‘elephantskin’).

67. Ocular Involvement
•Amajorcomplicationofonchocerciasishasbeenocularlesionsleadingto
blindness.
•Theprevalenceofblindnessdependsontheorganismstrainandthe
prevalenceofdiseasewithinanarea,whilethedegreeofeyeinvolvement
dependsonthedurationandseverityofinfection.
Inflammatoryreactionsintheeyeleadingtoocularonchocerciasis,
blindness.

68. Ocular onchocerciasis

69. Trichinellaspiralis
•Trichinellaspiralisisatissuenematodenormallyparasiticindomestic
andwildpigs,rats,andmanywildcarnivores
•Humaninfectioniscalled(trichinosis)(trichinellosis)andisazoonosis

70. Transmission
Human infection occurs when encysted Trichinellalarvae are
eaten in raw or undercooked meat, usually from an infected wild
pig .

71. Development in a human host
•HumaninfectionwithTrichinellaspiralisisazoonosis.
•Whenmanbecomesahost,thelifecycleends‘blindly’.

72. Trichinosis
•Within48hoursofingestingTrichinellalarvae,intestinaldisturbances
mayoccur.Thesecanincludeabdominalpain,nauseaandvomiting.
•Duringmigrationofthelarvae,allergicsymptomsdevelopincluding
fever,oedemaoftheface,headache,andeosinophilia
•Encystmentofthelarvaeoftencausesmusclepain
•Heavyinfectionwithwidespreadmigrationoflarvaemaycause
neurologicaldisordersandoccasionallyafatalmyocarditis

73. Muscle digestion