Pathogenesis of Parasitic Infections

Question 1

What are the 3 main species of Schistosomiasis?

Answer 1

Three main species:
•Schistosoma mansoni
•S. haematobium
•S. japonicum

Question 2

What is Schistosomiasis; cercarial dermatitis?

Answer 2

• Exposure to cercariae from animal or bird schistosomes
• Requires pre-sensitization
• Allergic-type reaction

Key feature of immune response is granuloma formation
•Eggs become organized in granulomas
•Repeated insults and tissue repair leads to fibrosis and organ damage

Question 3

What is pathology caused by in Hepato-intestinal schistosomiasis?

Answer 3

• Infections with S.mansoniand S. japonicum

* Pathology caused by immune response to eggs

Question 4

What do we know about Helminths: onchocerciasis?

Answer 4

• Major blinding disease
• Caused by filarial parasite (Onchocercavolvulus)
• Transmitted by blackflies

Question 5

What do we know about the pathology of Onchocerciasis?

Answer 5

•Repeated episodes of inflammation to presence of microfilariae leads to permanent damage and scarring in skin and eyes

Question 6

What drugs are used in the Control of parasite infections for protozoa, helminths and ectoparasites?

Answer 6

Protozoa:
Tinidazole
Metronidazole
Nitazoxanide
Benznidazole
Heavy metals (meglumine antimoniate)

Helminths:
Albendazole/mebendazole
Praziquantel
Ivermectin
Diethylcarbamazine
Pyrantel

Ectoparasites:
Ivermectin
Benzyl/malathion lotions

Question 7

How can we take Control of parasite infections?

Answer 7

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

For many parasite infections in an endemic settings, treatment must be given periodically over long periods of time because re-infections are rapid or because the treatment kills larval rather than adult stages

Question 8

Summarise the above lecture:

Answer 8

• Parasites are important infections of humans
• They have a worldwide distribution but are found predominantly in tropical regions among populations living in poverty
• Although there are effective treatments for most parasitic infections, limited investment still means limited treatment options and problems of drug toxicity for many infections.
• Poverty reduction and education interventions combined with drug treatments will control/eliminate many parasite infections.