Microbiology Cheat Sheet
Opportunists, Oncoviruses & Emergence
Opportunists, oncoviruses and emergence for NEET-PG: CD4 thresholds, PCP, HPV E6 E7, EBV Burkitt, HTLV-1, SARS-CoV-2 ACE2, Nipah, and Ebola.
MedNext Academy | 3 min read
Opportunists, Oncoviruses & Emergence
Opportunists, oncoviruses and emergence for NEET-PG: CD4 thresholds, PCP, HPV E6 E7, EBV Burkitt, HTLV-1, SARS-CoV-2 ACE2, Nipah, and Ebola.
This topic covers opportunistic infections predicted by the type of immune defect, the oncogenic viruses associated with human malignancy, and key emerging infectious diseases.
High-yield lines
- The nature of the immune defect predicts the opportunistic pathogen: CD4 deficiency favours Pneumocystis and Cryptococcus, while neutropenia favours Aspergillus and Candida.
- Pneumocystis jirovecii pneumonia occurs at CD4 below 200 and is diagnosed by GMS staining of bronchoalveolar lavage showing crushed ping-pong ball cysts.
- TMP-SMX is the drug of choice for both treatment and prophylaxis of Pneumocystis pneumonia, with prophylaxis started at CD4 below 200.
- Cryptococcal meningitis occurs at CD4 below 100 and the cryptococcal antigen lateral flow assay is the single most useful rapid diagnostic test.
- Toxoplasma encephalitis presents as multiple ring-enhancing basal ganglia lesions at CD4 below 100, with empirical pyrimethamine plus sulfadiazine.
- HPV E6 degrades p53 and HPV E7 inactivates Rb, with types 16 and 18 causing about 70 percent of cervical cancers.
- In high-risk HPV cancers, viral DNA integrates and disrupts the E2 gene, derepressing E6 and E7 oncogene expression.
- Epstein-Barr virus causes Burkitt lymphoma with a t(8;14) c-myc translocation and nasopharyngeal carcinoma via LMP-1 mimicking CD40 signalling.
- Hepatitis B causes hepatocellular carcinoma via HBx protein and integration, while hepatitis C causes it purely through chronic inflammation without integration.
- HHV-8 causes Kaposi sarcoma, primary effusion lymphoma, and multicentric Castleman disease.
- HTLV-1 Tax protein activates NF-kappaB and causes adult T-cell leukaemia with flower cells and hypercalcaemia.
- SARS-CoV-2 spike protein binds the ACE2 receptor, with TMPRSS2 facilitating entry, and RT-PCR on nasopharyngeal swab is the gold standard.
- Nipah virus is a BSL-4 paramyxovirus from Pteropus fruit bats causing encephalitis with respiratory involvement and Kerala outbreaks.
- Ebola virus is a BSL-4 filovirus transmitted by body fluid contact, prevented by the rVSV-ZEBOV ring vaccination strategy.
Mapped competency codes
- MI8.2
- MI8.3
- MI8.4
Continue into the full chapter
This summary maps to MI8-zoonotic-diseases-and-miscellaneous.
Frequently Asked Questions
How do HPV oncoproteins cause cancer?
E6 degrades p53 via the ubiquitin-proteasome pathway and E7 inactivates Rb, releasing E2F to drive cell cycle progression.
What stain is used for Pneumocystis and what does it show?
Gomori methenamine silver (GMS) stains the cyst wall black, giving a crushed ping-pong ball appearance on bronchoalveolar lavage.
Which receptor does SARS-CoV-2 use for entry?
The ACE2 receptor via the spike protein receptor-binding domain, with TMPRSS2 serine protease facilitating membrane fusion.
Which oncogenic virus does not integrate into the host genome?
Hepatitis C virus, which causes hepatocellular carcinoma purely through chronic inflammation without genomic integration.
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