Paper II — 2017 August (Supplementary) (2010 Scheme) — Q13
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Paper II
2017 August (Supplementary) (2010 Scheme) · 40 marks · 120 min
Question
Opportunistic parasitic infection
Q132 marksShort Notes
Answer
Opportunistic parasitic infections are parasitic diseases that are generally mild, self-limiting, or even subclinical in immunocompetent hosts, but cause severe, often life-threatening disease in immunocompromised individuals (particularly advanced HIV/AIDS), reflecting the critical role of intact cell-mediated immunity in controlling these organisms.
Important examples:
Cryptosporidium parvum — self-limiting diarrhoea in immunocompetent hosts; chronic, severe, life-threatening watery diarrhoea in AIDS (CD4 <100 cells/μL).
Toxoplasma gondii — usually asymptomatic/mild in immunocompetent hosts; causes toxoplasma encephalitis (from reactivation of latent infection) in advanced HIV/AIDS, an AIDS-defining opportunistic infection.
Isospora (Cystoisospora) belli — causes chronic diarrhoea in AIDS patients, similar in pattern to cryptosporidiosis.
Microsporidia (e.g., Enterocytozoon bieneusi) — cause chronic diarrhoea and wasting in advanced AIDS.
Leishmania donovani — visceral leishmaniasis can present atypically/severely and relapse frequently in HIV-coinfected individuals.
Strongyloides stercoralis — can cause a life-threatening hyperinfection syndrome/disseminated strongyloidiasis in immunocompromised hosts (notably those on corticosteroids or with HTLV-1 co-infection), due to the parasite’s unique autoinfective life cycle allowing internal amplification of the worm burden.
Clinical significance: recognition of this pattern is important both for guiding diagnostic suspicion in immunocompromised patients presenting with unexplained diarrhoea/systemic illness, and for informing screening/prophylaxis strategies (e.g., avoiding live-attenuated exposures, careful evaluation before corticosteroid therapy in patients from Strongyloides-endemic areas) in at-risk populations.
