Schistosomiasis

Question 1

Number of people infected with schistosomiasis.

Answer 1

200 million

Question 2

Percentage severe morbidity.

Answer 2

10%

Question 3

What host is each trematode from?
S.mansoni
S.haematobium
S.japonicum

Answer 3

S.mansoni - biomphalaria
S.haematobium - bulinus
S.japonicum - oncomelania

Question 4

Regions each species native to.

Answer 4

S.mansoni - Africa
S.japonicum - China
S.haematobium - America and Africa

Question 5

Species of schistosomiasis of importance in humans

Answer 5

S. mansoni, S.japonicum, S.haematobium, S.intercalatum, S.guineensis, S.mekongi

Question 6

West African schistosomiasis zoonosis detection.

Answer 6

Recent detection of novel hybrids between S.haematobium and S.bovis revealed unexpected zoonosis.

Question 7

Schistosomiasis life cycle.

Answer 7

Egg hatches > miracidium > miracidium penetrate snail intermediate > multiply in successive generations of sporocysts > snail releases free-swimming cercaria which penetrates host skin > cercaria tail falls off, forms a schistosomulum in skin tissue > enter circulation, travel to portal vein to mature to adults > paired adults migrate to mesenteric/bladder veins

Question 8

What are cercariae morphology adapted for?

Answer 8

Motility and penetrating unbroken skin with an acetabular gland which produces proteases and elastases.

Question 9

Aetiology of symptoms

Answer 9

From egg presence, 100s eggs released per day. Most released but some remain in tissue.
Immune response from soluble egg antigen (SEA), the immune response involves various cell types (T cells, B cells, eosinophils, mast cells, [granulomatous or multinuculated giant cells], macrophages) and cytokines.

Question 10

Pathophysiology of acute symptoms

Answer 10

Granulomatous reaction to eggs in mesentery/urogenital veins

Question 11

Symptoms of chronic infection

Answer 11

Hepatosplenomegaly, portal hypertension and varacies. Blood in urine/faeces.

Question 12

Diagnosis

Answer 12

Clinical presentation
Microscopic methods (Kato-Katz, Flotac, centifruged pr filtered urine/semen)
Parasite protein detection (CCA, CAA, SEA)
Haematuria (visible or cryptic)
Antibody detection - don’t indicate current infection concerns over sensitivity or specificity. Patterns of An and Ab can be confusing.

Question 13

Treatment of schistosomiasis

Answer 13

Praziqunatel (?voltage gated Ca2+ ion channels. This may damage worm tegument and expose surface to immune dependent attack)

Question 14

Limitations of praziquantel

Answer 14

• Active against adult worms alone, doesn’t reverse pathology.
• Tablets hard for children to swallow.
• Performance of drug enhanced with ingestion of fatty or high carb meals.
• Cure rates by praziquantel sensitive to baseline prevalence of infection (higher infection, the lower the cure rate), particularly true in pre-school children

Question 15

Why is there a need for mapping of schistosomiasis?

Answer 15

For effective control of disease by targeting resources. This is a fundamental concept in the WHO strategic plan for schistosomiasis.

Question 16

Methods of schistosomiasis control?

Answer 16

Vaccines/ Molluscicides/Prevention chemotherapy

Question 17

Schistosomiasis and vaccines

Answer 17

Glutathione-S-transferase (GST) has been investigated as a potential. GST based vaccines potentially don’t produce and appropriate response. Bourke et al (2014) showed performance varies on patient age and prior schistosomiasis/praziquantel exposure.

Question 18

Schistosomiasis and molluscicides

Answer 18

Expensive. Large ecological impact.

Question 19

Schistosomiasis and preventative chemotherapy

Answer 19

Large efforts in up-scaling drugs in sub-Saharan Africa. Single dose of praziquantel given to millions of children from improved political advocacy, and the increase of Merck’s donation from 25 to 250 million tablets a year.

Question 20

Why are school aged children prioritised for schistosomiasis treatment?

Answer 20

• Higher parasitaemia burden
• Greater vulnerability to disease
• Easier accessibility within educational infrastructure (attending primary school) as supported by universal primary education

Question 21

WHO recommendations regarding praziquantel treatment.

Answer 21

Schools in high risk areas (>50% parasitological methods, >30%questionnaires for frank haematuria) - all school age children annually, improve sanitation, water and health education
Schools in moderate risk areas (>10% and 1%

Question 22

Schistosomiasis treatment challenges.

Answer 22

• Treatment doesn’t prevent/guard against subsequent infections (pathology eggs induce diminished by reduction in their production)
• Schistosomiasis detection in infant/pre-school children that highlights other shortcomings in present control tools

Question 23

Why is socio-anthropology of interest to epidemiology?

Answer 23

Cultural KAP may inhibit success of otherwise logical disease interventions. Information, education, communication.

Question 24

Barriers to disease acceptance.

Answer 24

Disease aetiology unknown, not recognised as low perceived morbidity, not known as disease can be prevented, other priorities (e.g harvesting(, limited resources (time/money/materials) to take effect, solutions may undermine standing of existing community leaders/doctors

Question 25

Kick out Kichoco. What is it?

Answer 25

2003-2007, Zanzibar. Aimed to provide praziquantel, monitor disease and develop appropriate strategies for health education. Books with locally attractive story lines printed for children to improve awareness and reduce bad behaviours.
Result: Knowledge didn’t improve, practice of urinating in water decrease (from survey data)