This document provides an overview of helminthic infections, highlighting the modes of entry, life cycles, and clinical features of various parasitic worms. It emphasizes the role of host factors in the expression of disease and outlines treatment options for conditions like trichinosis and schistosomiasis. The material is available under a Creative Commons license and includes a caution for graphic medical content.

1. Author(s): Vernon Carruthers, Ph.D., Cary Engleberg, M.D., D.T.M.&H., 2009
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3. Helmintic Infections
M1 Infectious Diseases Sequence
Vernon Carruthers
Cary Engleberg
Spring 2009

4. Infection vs. disease
• successful parasites live in, but do not
kill their hosts
• protozoa multiply within hosts
expression of disease depends on host
factors
• helminths do not multiply within hosts
severity of disease depends on parasite
burden and immunologic response to
parasites
3

5. Helminth forms
Larva
Egg
Cyst
Adults
4
C. Engleberg/V. Carruthers

6. Helminth modes of entry
• Ingestion (eggs or cysts)
• Arthropod bites (larvae)
• Penetration of intact skin or
mucous membranes (larvae)
5

7. Spread and tropisms
• Some parasites must migrate to
certain locations within the host
in order to complete their life
cycle
• Non-human parasites, in humans,
often fail to migrate properly and
become dead-end infections
6

8. Cary Engleberg
7

9. Mechanisms for evading the host response
• antigenic variation - trypanosomes, malaria,
giardia
• intracellular infection - malaria, toxoplasma
• encystation* - Toxoplasma, cestodes
• camouflage - schistosomes
• cleavage of ABs or C components - amoebae,
leishmania
• suppression/redirection of the cellular immune
response - malaria, leishmania, schistosomes
* cyst has multiple meanings 8

10. Tissue damage and host
response
• direct destruction of tissue
• hypersensitivity reactions
• eosinophila
– occurs with helminths, not protozoa
– results from tissue migration
9

11. Classification of helminths
Nematodes (roundworms)
Platyhelminthes (flatworms)
Trematodes ( flukes )
Cestodes ( tapeworms )
C. Engleberg/V. Carruthers
10

12. Helmintic diseases
• Intestinal
– Others
– Strongyloides (autoinfection cycle)
roundworms • Invasive
– Trichinosis (muscle pain, uncooked carnivores)
– Filaria (worms in lymphatics or under skin)
flukes – Schistosomiasis (liver or urinary tract
granulomas and fibrosis)
tapeworms
– Cysticercosis (cysts in brain, seizures)
– Echinococcus (massive cysts in liver or lung)
11

13. Intestinal nematodes
Adult worms in the
the intestine
Larvae pass
through lungs
Trichiuris (whipworm)
Enterobius (pinworm)
Larvae enter Eggs
bloodstream Eggs ingested
ascaris
strongyloides
hookworm Larvae hatch
Larvae penetrate
from eggs
through intact skin
C. Engleberg/V. Carruthers
12

14. Strongyloides life cycle
Adult worms in the
the intestine
Larvae pass
through lungs
Larvae enter Eggs
bloodstream Autoinfection
1st stage
Larvae penetrate larvae hatch
through intact skin Larvae molt from eggs
twice to form
filariform larvae 13
C. Engleberg/V. Carruthers (infectious)

15. Source Undetermined
14

16. Strongyloides - clinical features
• uncomplicated
– GI upset
• autoinfection
• hyperinfection
– rash
– bronchspasm, chest X-ray infiltrates
– diarrhea
– profound eosinophilia
– recurrent Gram-negative bacteremia 15

17. Trichinosis
16

18. Trichinella spiralis - life cycle
• cycle of carnivorism among hogs and rats
• humans ingest encysted larvae in infected,
undercooked pork
• larvae exist in stomach and burrow into small
intestinal mucosa
• adult males and female reemerge and produce
larvae which penetrate intestine and circulate in
bloodstream
• larvae enter skeletal muscle cells and encyst
17

19. Source Undetermined Source Undetermined
18

20. Trichinosis cases, by source of
infection, U.S.,1981
Pork products
sausage 93
other 44
unspecified 9
Non-pork products
hamburger 18
bear 10
other wild animals 7
Unknown 7
188 19

21. Clinical features of trichinosis
• Most common sxs:
– muscle pain and tenderness
– fever +/- chills
– edema (often periorbital)
• >10% eosinophilia (often ~50%)
• elevated creatine phosphokinase (CPK)
• +/- chronic neurologic/myocardial sxs
• self-limited (2% mortality)
20

22. Treatment of trichinosis
• antihelmintic (albendazole) to kill
any intestinal adults
• steroids to relieve inflammatory
reactions
• antipyretics
21

23. Filaria
22

24. Life cycles of two types of
filaria
Arthropod Adult Larvae
vector worm pairs (microfilariae)
Lymph- mosquitoes peripheral circulate
dwelling lymphatics in bloodstream
(e.g, Wuchereria
bancroftii )
Skin- biting flies skin nodules migrate through
dwelling or migratory dermis
23

25. Microfiliaria found in the blood of
lymph dwelling species
Armed Forces Institute of Pathology
24

26. Long-term
consequences of
persistent lymph-
dwelling filarial
infection:
Blockage of lymph
drainage with
chronic lymphedema
(elephantiasis)
Source Undetermined
25

27. Source Undetermined
26

28. Life cycles of two types of
filaria
Arthropod Adult Larvae
vector worm pairs (microfilariae)
Lymph- mosquitoes peripheral circulate
dwelling lymphatics in bloodstream
(e.g, Wuchereria
bancroftii )
Skin- biting flies skin nodules migrate through
dwelling or migratory dermis
(e.g., Onchocerca
volvulus &
Loa loa )
27

29. Source Undetermined
Black fly: vector of Onchocerciasis
28

30. O. volvulus microfilaria (a skin-
dwelling species) in skin snip
Snip site
Source Undetermined
Depigmentation due to chronic
microfilarial production, degradation, and
allergic host responses in the skin
Cary Engleberg
29

31. Cary Engleberg
30

32. Source Undetermined
O. volvulus skin nodule removed and sectioned,
showing cross-sections of male and female
adult worms (source of microfiliariae)
31

33. Source Undetermined
Onchocerciasis ( River blindness ) 32

34. Role of endosymbiont Wohlbachia
sp. in filiaria infection
• Rickettsia-like organisms required
for fecundity and viability of filaria
• Wohlbachia-free worms produce
less inflammation in tissue (? LPS)
• Implications for rx:
– ivermectin kills microfilaria only
– tetracycline may destroy adult worms
33

35. Schistosomiasis
34

36. Geographic distribution of
schistosomiasis
S. mansoni
S. hematobium
S. japonicum
35
Cary Engleberg

37. Schistosomiasis - life cycle
Eggs
Cercaria
S.m. S.h. S.j.
(snail) Pearson Scott Foresman, wikimedia commons
36
Cary Engleberg (All other images)

38. Source Undetermined
Source Undetermined Source Undetermined
S. mansoni S. haematobium S. japonicum
37

39. Source Undetermined
38

40. Events following cercarial penetration
1. Larva migrate to lungs and develop as
schistosomulae (this may trigger a self-
limited febrile illness).
2. Male and female schistomulae migrate to the
abdominal venules:
I. Superior mesenteric (S. japonicum)
II. Inferior mesenteric (S. mansoni)
III. Bladder plexus (S. hematobium)
3. Males and females pair off and egg production
begins
4. Eggs migrate out of the body through visceral
organs or become trapped and die in tissues.
39

41. Immune response to
schistosoma infection
Source Undetermined
40

42. Source Undetermined
41

43. Source Undetermined
42

44. Source Undetermined
43

45. Source Undetermined
44

46. Source Undetermined
45

47. Source Undetermined
pipestem fibrosis
46

48. Source Undetermined
47

49. Schistosomiasis - pathogenesis
• egg granuloma (type IV reaction)--> fibrosis
• morbidity ~ worm (egg) burden
• concomitant immunity to schistosomula
• adult worms: invisible to the immune
system (survive for years)
48

50. Schistosomiasis- clinical features
• Cercarial dermatitis
• Intestinal schistosomiasis (granulomas -->
polyps, protein loss, malabsorption, strictures)
• Hepatosplenic schistosomiasis (portal
hypertension --> ascites, varices, splenomegaly,
normal hepatic function)
• Urinary schistosomiasis (hematuria, chronic
infection, obstruction)
• Other (cardiopulmonary, CNS, etc.)
49

51. Drug treatment of
schistosomiasis
• Praziquantel increases permeability
of adult parasite to Ca++.
• Tetanospasm --> death
50

52. Cestode infections
51

53. Tapeworms
• Definitive hosts: harbor adult worms
• Intermediate hosts: harbor tissue cysts
(containing worm heads)
• Humans acquire infection two ways:
– ingestion of eggs from feces (to acquire
tissue cysts) = Intermediate host
– ingestion of tissue cysts in undercooked
meat (to acquire a tapeworm) = Definitive host
52

54. Taeniasis poor
sanitation
ingestion of
undercooked pork
poor
hygiene
Tapeworm Cysticercosis
(pig) Martin von Nathusius, wikimedia commons
53
Cary Engleberg (All other images)

55. Source Undetermined
54

56. Source Undetermined
55

57. Source Undetermined
56

58. Source Undetermined
57

59. Cysticerci Hydatid Cyst
C. Engleberg/V. Carruthers
58

60. Isolated cysticerci Hydatid cyst
Source Undetermined
Source Undetermined
59

61. Source Undetermined
Duane Newton 60

62. Echinococcosis ingestion of
eggs in
pastures
ingestion of
entrails
contact
with
dogs
(dog) Abujoy, wikimedia commons Cystic Hydatid Disease
(sheep) wikimedia commons 61
Cary Engleberg (All other images)

63. Cary Engleberg
62

64. Treatment of cysticercosis and
echinococcosis
• Antihelminthic therapy (e.g.,
albendazole, praziquantel)
• (Echinococcus only)
– Surgical removal
– Irrigation-evacuation of cysts
63

65. Comparison of pork tapeworm
and Echinococcus life cycles
Definitive
hosts Dog Dead-end
(adult Human hosts
tapeworms)
Human
Human
Intermediate
hosts Sheep
(tissue cysts)
Pig
C. Engleberg/V. Carruthers
64

66. Additional Source Information
for more information see: http://open.umich.edu/wiki/CitationPolicy
Slide 5: Cary Engleberg and Vernon Carruthers
Slide 8: Cary Engleberg
Slide 11: Cary Engleberg and Vernon Carruthers
Slide 13: Cary Engleberg and Vernon Carruthers
Slide 14: Cary Engleberg and Vernon Carruthers
Slide 15: Source Undetermined
Slide 19: Sources Undetermined
Slide 25: Armed Forces Institute of Pathology, http://www.afip.org/index.html
Slide 26: Source Undetermined
Slide 27: Source Undetermined
Slide 29: Source Undetermined
Slide 30: Cary Engleberg (left) Sources Undetermined (right)
Slide 31: Cary Engleberg
Slide 32: Source Undetermined
Slide 33: Source Undetermined
Slide 36: Cary Engleberg
Slide 37: (snail) Pearson Scott Foresman, Wikimedia Commons, http://commons.wikimedia.org/wiki/File:Snail_(PSF).png; Cary Engleberg All other images)
Slide 38: Sources Undetermined
Slide 39: Source Undetermined
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Slide 43: Source Undetermined
Slide 44: Source Undetermined
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Slide 48: Source Undetermined
Slide 54: (pig) Martin von Nathusius, Wikimedia Commons, http://commons.wikimedia.org/wiki/File:Cochon.svg; Cary Engleberg (All other images)
Slide 55: Source Undetermined
Slide 56: Source Undetermined
Slide 57: Source Undetermined
Slide 58: Source Undetermined
Slide 59: Cary Engleberg and Vernon Carruthers
Slide 60: Sources Undetermined
Slide 61: Duane Newton, University fo Michigan
Slide 62: (dog) Abujoy, Wikimedia Commons, http://commons.wikimedia.org/wiki/File:Dog_silhouette.svg, CC:BY-SA,
http://creativecommons.org/licenses/by-sa/2.5/deed.en ; (sheep) Wikimedia Commons,
http://commons.wikimedia.org/wiki/File:LA2-Blitz-Ostfriesisches_Milchschaf.png ; Cary Engleberg (All other images)
Slide 63: Cary Engleberg
Slide 65: Cary Engleberg and Vernon Carruthers