61. Pathogenesis of Parasitic Infections

Question 1

Pathogenesis of cutaneous leishmaniasis

Answer 1

ACUTE LESIONS

• Tissue damage caused by inflammatory response to presence of parasites in macrophages
• Parasite killing by Th1 pro-inflammatory responses and macrophage killing.

LATENCY
- Parasites remain present long-term. Regulatory immune response characterized by balance of Th1 and anti-inflammatory responses

RELAPSE (RARE)
- Alteration in immune response (i.e change in Th1 vs. immune regulation secondary to HIV, malnutrtition) may trigger relapse
•Mucocutaneous disease associated with strong but inadequate inflammatory response to parasites that have metastasized to mucosa
•Diffuse cutaneous leishmaniasis associated with uncontrolled parasite replication.
• Recividans – recurrence of lesions at old ulcer site.

Question 2

Schistosomiasis

Answer 2

Three main species

• Schistosoma mansoni
• S. haematobium
• S. japonicum

•Cercarial dermatitis
•Urinary Schistosomiasis
- Haematuria
- Bladder damage

Question 3

Helminths: onchocerciasis

Answer 3

• Major blinding disease
• Caused by filarial parasite (Onchocerca volvulus)
• Transmitted by blackflies
  ~ The vector: Simulium

• Onchocercal nodules
• Skin disease
  - Acute papular onchodermatitis
  - Chronic onchodermatitis
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•Eye disease
  - Anterior segment
     ~ Punctate keratitis
     ~ Acute iridocyclitis
     ~ Sclerosing keratitis
- Posterior segment
     ~ Optic neuritis/atrophy
     ~ Chorioretinopathy

Question 4

Control of parasite infections

Answer 4

•DRUGS

BEHAVIOURS
•Education
• Hand washing and hygiene behaviours

ENVIRONMENTAL INTERVENTIONS
•Spraying of residual insecticides for household vectors
•Mosquito nets for malaria
•Improved housing
•Sewage disposal and potable water
•Drainage of swamps

POVERTY REDUCTION
•Micro-financing, etc