L16: Secernenetea Flashcards
Give the two orders of Secernenetea
O. Rhabditida - Strongyloides
O. Strongylida - bursate nematodes
What is the causal agent of Strongylodiasis
Mainly the nematode Strongyloides stercoralis - infects humans, but also primates, and dogs
Other Strongyloides include S. fülleborni, which infects chimpanzees and baboons and may produce limited infections in humans
Give the geographic distribution of S. stercoralis
Tropical and subtropical areas, but cases also occur in temperate areas (including the South of the United States).
More frequently found in rural areas, institutional settings, and lower socio-economic groups
100M human infections; <3% sero-prevalence in Jamaica (3% of Jamaicans harbor strongyloides antibodies)
What group of persons are particularly affected by Strongylodiasis
The Immunocompromised
Give the reason for there only being females in the S. stercoralis life cycle
The female worm reproduces parthegenically giving rise to only females (2-4mm)
Additionally males only exist in the free-living life cycle of the parasite
Where is S stercoralis usually found
Feeding on the tissue of the duodenum (Anterior end of the small intestine)
Give the diagnostic feature of S stercoralis
L1 larvae in the stool
What is meant by the term autoinfection
Increasing intensity of infection in the body without coming in contact with external sources of infection
What are the clinical signs of Strongylodiasis
Frequently asymptomatic.
Dermatologic manifestations include:
Larva currens by L3; 10cm in1 hour!
Urticarial rashes in the buttocks and waist areas
Pulmonary symptoms can occur during pulmonary migration of the filariform larvae (L3) e.g. coughing, blood in sputum
Gastrointestinal symptoms include abdominal pain and diarrhea.
Disseminated strongyloidiasis due to increased rate of autoinfection occurs in immunosuppressed patients (e.g. HTLV-I infection, severe malnutrition, immunosuppressive drugs)
This can present with abdominal pain, distension, shock, pulmonary and neurologic complications and septicemia, and is potentially fatal.
Blood eosinophilia is generally present during the acute and chronic stages, but may be absent with dissemination.
Describe the process of making a laboratory diagnosis of Strongylodiasis along with treatment and preventative measures
Laboratory Diagnosis:
Diagnosis rests on the microscopic identification of larvae (rhabditiform and occasionally filariform) in the stool or duodenal fluid.
The duodenal fluid can be examined using techniques such as the Enterotest string test or duodenal aspiration.
Larvae may be detected in sputum from patients with disseminated strongyloidiasis.
Enzyme immunoassay may also be used (anti - S. stercoralis IgG)
Give the clinical features of Hookworm’s disease
Local skin manifestations (“ground- itch“ or “cutaneous larva migrans”) can occur during penetration by the filariform (L3) larvae – ~10 cm in 24 hours (c.f. Strongyloides)
Respiratory symptoms can be observed during pulmonary migration of the larvae (= Strongyloides)
Gastrointestinal and nutritional/ metabolic symptoms can also occur e.g. protein-losing enteropathy
Iron deficiency anemia (caused by blood loss at the site of intestinal attachment of the adult worms) is the most common symptom of hookworm infection
A. duodenale 0.15 mL blood/day
N. americanus 0.03 mL blood/day
Give the process of Lab diagnosis with hookworm infection
Laboratory Diagnosis:
Microscopic identification of eggs in the stool is the most common method for diagnosing hookworm infection.
However, examination of the eggs cannot distinguish between N. americanus and A. duodenale.
Larvae can be used to differentiate between N. americanus and A. duodenale –
Imperative to distinguish Strongyloides stercoralis
What drug may be used to treat creeping eruptus?
Mebendazol
Give the treatment for hookworm infection
Hookworm infections are generally treated with albendazole.
Mebendazole or pyrantel pamoate can also be used.
Give the treatment of Strongylodiasis
The drug of choice for the treatment of uncomplicated strongyloidiasis is ivermectin, with thiabendazole as an alternative.
All patients who are at risk of disseminated strongyloidiasis should be treated for fear of fatality.
Explain the three pathways within the S. stercoralis lifecycle
https://youtu.be/iQMwziCLyCs
Give the causative agents of hookworm infection
The human hookworms include two intestinal nematode (roundworm) species, Ancylostoma duodenale and Necator americanus.
Define the geographic distribution of hookworm infection
The second most common human helminthic infection (after ascariasis)
740 - 1300M people infected
DALY = 22.1M which makes hookworm infection clinically the most important intestinal nematode infection
Worldwide distribution, mostly in areas with moist, warm climates.
N. americanus predominates in the Americas and Australia, while only A. duodenale is found in the Middle East, North Africa and southern Europe.
Occurs in Jamaica <5%
Differentiate between A. duodenale and N. americanus
A. duodenale: 9 to 13 mm posterior cutting plates and anterior teeth
N. americanus: 8 to 11 mm anterior teeth and posterior cutting plates
Describe the A.duodenale lifecyle
https://www.youtube.com/watch?v=VSRQBc2SR48&ab_channel=QworldMedicalEducation
Name the structure which allows for copulation between hookworms
Copulatory bursa
Give the common reasons for transmission of hookworm infection
Combination of poor sanitation and appropriate environmental conditions required for high endemicity
Multiple returns to secluded area to defecate contributes to reinfection
Frost kills larvae and eggs
Alternative cycles of drying and wetting also kills larvae
…..also urine
Highest prevalences and intensities amongst teenagers and middle-aged individuals – c.f. Trichuris and Ascaris – affects control strategy? Still targetted?
Infected individuals often crave red dirt (high iron content)
Give a general description of Haemonchosis
Called the “Barber–pole worm” (white ovary twisted around red, blood-filled intestine)
Occurs in 4th stomach of sheep, cattle, goats, etc
Common in Jamaica
Rare in man
Important veterinary parasite
Adults feed on blood – cause severe anaemia
Infection occurs through ingestion of L3 with forage
ppp = 20 days
Untreated heavy infections usually fatal
Survivors usually elicit “self-cure” – immune response to release worm antigens
Potential anthelmintic resistance shown against benzimidazoles and ivermectin
Give a general description of Ostertagiosis
Ostertagia ostertagia – dirty brown colour
also called ‘brown stomach worm” ~3 cm long
Common in Jamaica
Similar to Haemonchus in host, infective stage and location
Feed on blood in 4th stomach
Cause anaemia, but not so severe as Haemonchus
Albendazole treatment
Human infections rare – arise from ingestion of undercooked tripe (ingestion of adult worms)
Economic losses in cattle industry exceed $600m in USA alone
