L16: Secernenetea

Question 1

Give the two orders of Secernenetea

Answer 1

O. Rhabditida - Strongyloides

O. Strongylida - bursate nematodes

Question 2

What is the causal agent of Strongylodiasis

Answer 2

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

Question 3

Give the geographic distribution of S. stercoralis

Answer 3

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)

Question 4

What group of persons are particularly affected by Strongylodiasis

Answer 4

The Immunocompromised

Question 5

Give the reason for there only being females in the S. stercoralis life cycle

Answer 5

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

Question 6

Where is S stercoralis usually found

Answer 6

Feeding on the tissue of the duodenum (Anterior end of the small intestine)

Question 7

Give the diagnostic feature of S stercoralis

Answer 7

L1 larvae in the stool

Question 8

What is meant by the term autoinfection

Answer 8

Increasing intensity of infection in the body without coming in contact with external sources of infection

Question 9

What are the clinical signs of Strongylodiasis

Answer 9

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.

Question 10

Describe the process of making a laboratory diagnosis of Strongylodiasis along with treatment and preventative measures

Answer 10

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)

Question 11

Give the clinical features of Hookworm’s disease

Answer 11

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

Question 12

Give the process of Lab diagnosis with hookworm infection

Answer 12

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

Question 13

What drug may be used to treat creeping eruptus?

Answer 13

Mebendazol

Question 14

Give the treatment for hookworm infection

Answer 14

Hookworm infections are generally treated with albendazole.

Mebendazole or pyrantel pamoate can also be used.

Question 15

Give the treatment of Strongylodiasis

Answer 15

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.

Question 16

Explain the three pathways within the S. stercoralis lifecycle

Answer 16

https://youtu.be/iQMwziCLyCs

Question 17

Give the causative agents of hookworm infection

Answer 17

The human hookworms include two intestinal nematode (roundworm) species, Ancylostoma duodenale and Necator americanus.

Question 18

Define the geographic distribution of hookworm infection

Answer 18

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%

Question 19

Differentiate between A. duodenale and N. americanus

Answer 19

A. duodenale: 9 to 13 mm posterior cutting plates and anterior teeth
N. americanus: 8 to 11 mm anterior teeth and posterior cutting plates

Question 20

Describe the A.duodenale lifecyle

Answer 20

https://www.youtube.com/watch?v=VSRQBc2SR48&ab_channel=QworldMedicalEducation

Question 21

Name the structure which allows for copulation between hookworms

Answer 21

Copulatory bursa

Question 22

Give the common reasons for transmission of hookworm infection

Answer 22

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)

Question 23

Give a general description of Haemonchosis

Answer 23

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

Question 24

Give a general description of Ostertagiosis

Answer 24

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

Question 25

Give a general description of Dictyocauliasis

Answer 25

Dictyocaulus viviparus – “cattle lung worm” causing “hoose”
Important parasite of cattle
adults live in respiratory tracts – feed on blood
Infection acquired by ingestion of L3 with fodder
L4 penetrates gut, lymph ducts, blood, lungs, bronchioles
Untreated infections cause death due to dyspnoea and pneumonia
D. filaria – sheep and goats
D. arnfieldi – horses
Ivermectin treatment

Question 26

Describe the Life cycle of A. cantonensis

Answer 26

https://www.youtube.com/watch?v=X_u5vfjxzyo&ab_channel=Bioscience

Question 27

Account for the significance of Angiostrongylus cantonensis

Answer 27

Related to hookworms – a metastrongyl
A. cantonensis was first discovered in the pulmonary arteries of rats in China in 1935
10 years later, worms were found in the spinal cord of a 15 y.o. boy in Taiwan
Since then the parasite has spread significantly, and is now in the New World
Occurs in <40% wild rats in Jamaica
Responsible for eosinophilic meningitis in humans here, and elsewhere

Question 28

Describe the process of diagnosis of A.cantonensis

Answer 28

Based on clinical symptoms and eosinophilia
Confusion with other [bacterial, viral, helminth] infections?
Pain killers and steroids – thiabendazole?
Dead adults in brain pose a real problem for treatment

Question 29

Explain some preventative measures for A cantonensis

Answer 29

An emerging infection in Jamaica
Risk behaviour is consumption of raw snails/crustaceans
e.g. “strong man drinks”
or unwashed raw vegetables e.g. case with 2000 outbreak among “spring-breakers” in Jamaica

Question 30

Explain the pathological complications associated with A cantonensis in man

Answer 30

Worms lodge in brain, meninges (and lungs) of humans
Eosinophilic meningoencephalitis
Eosinophilia and leukocytosis of blood and CSF
Headache, fever, stiff neck, paralysis, coma, death
Destruction of brain and spinal cord cells by immune responses evoked by dead worms
< 40 [known] cases in Jamaica in last 10 years
Several deaths recorded, also in Jamaica

Question 31

Give a brief account of A cantonensis history of infection in Jamaica

Answer 31

1994 First case of EM reported in Jamaica in a 31-year-old female, St. Ann.
Recovered. Barrow et al. (1996)
2000 A 14-month-old boy, Kingston. Fatal. Lindo et al. (2004)
Outbreak in Montego Bay: 12 cases: nine hospitalized/two serious
Recovered with serious sequelae. Slom et al. (2002)
2001 American tourist contracts EM in Jamaica Recovered King (2001)
2003 A 27-year-old male prisoner, St. Elizabeth Fatal T. Ferguson, personal
communication
2004 A 19-month-old female, from St. Catherine, diagnosed in Kingston
Permanent neurological damage. Evans-Gilbert et al. (2014)
2007 An 8-year-old male diagnosed Kingston. Recovered. Evans-Gilbert et al. (2014)
2008 A 24-month-old male diagnosed in Kingston. Recovered.
A 19-month-old male diagnosed in Kingston. Recovered
A 12-month-old female diagnosed in Kingston. Hemiparesis
An 8-year-old male diagnosed in Kingston. Recovered. Evans-Gilbert et al. (2014)
2009 A 30-year-old female; ocular angiostrongylosis; diagnosed in Kingston. Recovered. Mattis et al. (2009)
2013 A 19-month-old infant diagnosed in Kingston. Permanent neurological
damage. Evans-Gilbert et al. (2014)