Order Strongylida
• Hookworms
– Necator americanus
• Americas, Africa, Asia
– Ancylostoma duodenale
• Europe, Northern Africa,
Asia, Americas
– Ancylostoma braziliensis
• Carnivores in the tropics
• Cutaneous larval
migrans/creeping eruption
– Ancylostoma caninum
• Canids
• Cutaneous larval
migrans/creeping eruption
•Free-living
Juveniles
•Filariform
are
infective
Rhabditiform and Filariform J3’s
•Filariform
are
infective
•Filariform
are
infective
Necator americanus
Ancylostoma duodenale
Necator americanus
Ancylostoma duodenale
Transmission
• Ancylostoma duodenale
–
–
–
–
–
Cutaneous
Oral ingestion of juveniles
Paratenic hosts
Transmammary
Transplacental?
• Necator americanus
– Cutaneous
Hookworm Disease
•
•
•
1300 million people infected
160 million experience illness
Severity depends on:
1. Number of worms
2. Species infected with
3. Nutritional status of host
Hookworm Disease
• Necator americanus
< 25 no symptoms
25-100 light symptoms
100-500 moderate symptoms
500-1000 severe symptoms
> 1000 Very severe, often fatal
• Ancylostoma duodenale
100+ severe symptoms
Pathogenesis
1. Cutaneous Phase
•
•
•
Juveniles enter skin
Entrance into blood vessels initiates tissue
reaction that can kill juveniles
Itching/rash at location of penetration
•
•
Caused by bacteria
“Ground itch”
Pathogenesis
2. Pulmonary Phase
•
•
•
•
Juveniles enter alveoli and move up bronchi
to throat
Usually asymptomatic
Hemorrhaging
Dry cough
Pathogenesis
3. Intestinal Phase
•
•
•
Adults enter intestine
Attach to mucosa with teeth
Feed on blood
Pathogenesis
3. Intestinal Phase
•
•
•
Adults enter intestine
Attach to mucosa with teeth
Feed on blood
Adults pull in a plug of tissue and suck
blood!
Pathogenesis
• Blood loss extensive
– Lesions
– Anticoagulants
• Blood loss exceeds what worms ingest
– Necator americanus
• 0.03 ml/worm/day
– Ancylostoma duodenale
• 0.15-0.26 ml/worm/day
Small Intestine Infected with
Hookworms: They are sloppy feeders!
Pathogenesis
• Heavy infections
–
–
–
–
–
–
Anemia (Iron Deficiency Anemia)
Severe protein deficiency
Edema
Stunting
Mental dullness
Heart failure
Hookworm disease: statue (A) and child (B) from Costa Rica
with typical stance caused by malnutrition and severe
hookworm infection. (Courtesy of Dr. Herman Zaiman and
Muriel Jones).
Iron Deficiency Anemia
• Decrease in erythrocyte count due to lack of
iron
• Less oxygen gets to tissues
• 2 billion people
Iron Deficiency Anemia
• Affects:
• Protein-energy malnutrition
– Growth and development of children
• Physical
• Cognitive
– Pregnancy
• Risk of death of mother and child
• Low birth weight
• Premature birth
– General health
•
•
•
•
Loss of energy
Weakness
Shortness of breath
Mental dullness
• “The disease induced by the
hookworm…was never suspected to be a
disease at all. The people who had it were
merely supposed to be lazy, and were
therefore despised and made fun of, when
they should have been pitied.”
- Mark Twain (Letters from the Earth)
Diagnosis
• Demonstration of eggs in fecal smear
• Cannot distinguish species by eggs
Melenic diarrhea!
Frank blood in diarrhea!
Treatment
•
•
•
•
Mebendazole
Single dose effective
Iron supplementation
Drug resistance of N.
americanus in Africa
Epidemiology
• How do you get infected?
• Necator americanus
– Juveniles penetrate skin
• Ancylostoma duodenale
–
–
–
–
–
Juveniles penetrate skin
Ingest juveniles orally
Paratenic host
Transmammary
Transplacental
Epidemiology
• Transmission
• Environmental conditions
– Need
• Moisture
• Warm temperature
• Shade
– Juveniles live in moisture in the soil
• Migrate to stay in optimal conditions
• Dry: Move downward
• Wet: Move upward to surface of soil extend upward “looking
for a host”
– Live 3 weeks
Epidemiology
• Common in tropical or subtropical areas
• i.e. Southeastern U.S.
Robert, LA
Transmission “Hot spots”
• Mines
• Coffee, banana, sugarcane plantations
Other Hookworm Species
• Ancylostoma braziliensis
– Domestic and wild carnivores in tropics
– Most common cause of cutaneous larval
migrans/creeping eruption in humans
• Ancylostoma caninum
– Adults occur in canids (infrequently humans)
– cutaneous larval migrans/creeping eruption in
humans
Ancylostoma caninum
Cutaneous Larval Migrans/ Creeping
Eruption
• Juveniles penetrate skin
• Cannot complete
migration
• Tunnel through skin
• Secondary infection
• Weeks-months
Cutaneous Larval Migrans/ Creeping
Eruption
Soil Born Nematodes
• “Soil born” nematodes or “Geohelminths”
– Ascaris sp.
– Trichuris trichiura
– Necator americanus
– Ancylostoma duodenale
“Soil-born” Nematodes
• Development to infective stage
• Ascaris sp.
– Eggs embryonate in soil
• Trichuris trichiura
– Eggs embryonate in soil
• Necator americanus
– Eggs embryonate in soil
– Juveniles develop in soil
• Ancylostoma duodenale
– Eggs embryonate in soil
– Juveniles develop in soil
Epidemiological Model of Soil-Born Nematodes
Development
to infective
stage
Infected
people
1. Contact
2. Contact
Soil
Uninfected
people
1. Eggs released with feces of infected human. Eggs develop in the
environment, commonly in soil. Development to the infective stage
must occur for successful transmission.
2. Human contacts infective stage. How does this contact differ among
species discussed?
Sensitivity to Environmental Conditions
•
Rank the species according to their
sensitivity
1. Ascaris sp.
2. Trichuris trichiura
3. Hookworm species
•
How is sensitivity going to effect their
distribution?
Distribution
Warm moist
habitat
Ascaris sp.
Trichuris
Hookworms
Distribution
Warm moist
habitat
Ascaris sp.
Trichuris
Hookworms
Southeastern
United States
Okefenokee Swamp, GA
• Warm temperatures
• High Rainfall
– Moisture
– Runoff
• Dense vegetation
– Shade
• High humidity
Outhouses
Socioeconomic status
• Poverty
• Attitude
Scotlandville, LA
• Parasite survey of school children 1974
– 27% Ascaris lumbricoides
– 22% Trichuris trichiura
– 4% Hookworms
• Which families are infected with parasites?
• Is poverty correlated with infection in
Scotlandville?
• What is the cause and effect relationship?
• Sick people
• Poor facilities
Parasitism
• Economic loss
•Treatment
• Lack of clean
water
•Lost days of
work
• Food quality
Poverty
•Reduced
cognitive
abilities
Summary
• Different way of life
• Climate
– Temperature
– Water
– Vegetation
• Poverty
– Correlates with parasitism
– Sewage disposal
– Reflected in attitude
• Close to home
Geophagy
Geophagy
•
•
•
•
Ingestion of soil
Historical practice
Modern practice in Africa and SE U.S.
Special types of soil are sold
– Clay based soil
• Markets in Georgia, parts of Africa, and parts of
South America sell soil for consumption.
• Intense cravings for soil
– 55 yr old woman who would eat only soil if she could
Why?
• Pregnancy
• Cure for ailments
• Religious practice
• Clay soils contain kaolin, the principal ingredient in
Kaopectate.
– Morning sickness
– Intestinal ailments
• Nutritional supplement
–
–
–
–
Iron
Magnesium
Calcium
Phosphorus
Geophagy
• Geophagy is often correlated with
– Anemia
– Parasite infection
• Cause and effect?
–
–
–
–
–
Does anemia cause geophagy?
Does parasitic infection cause geophagy?
Does geophagy cause anemia?
Does parasitic infection cause anemia?
Does geophagy cause parasitic infection?
Geophagy and Parasitism
• Western Kenya
Geophagic
Non-geophagic
44%
48 (13-133)
37%
20 (7-37)
16%
2413 (1055-6903)
9%
455 (25-920)
Trichuris trichiura
Prevalence
Egg per gram (range)
Ascaris lumbricoides
Prevalence
Egg per gram (range)
Geissler et al. 1998. Transactions of the Royal Society of Tropical Medicine
and Hygiene 77: 432-438.
Summary
• Geophagy is a relatively common practice
• Geophagy is associated with parasitism
– Geophagy causes parasitism
– Does parasitism cause geophagy?
Questions?
• What are the species of “soil-born”
nematodes?
• Why is Enterobius vermicularis not a “soilborn” nematode?