Viruses and Protozoa

What are viruses classified as in terms of cellular structure?

Obligate intracellular parasites that do not grow but replicate only inside host cells.

How do viruses use host cells?

They exploit host metabolism for replication, using cell receptors for entry.

What are the main routes of viral transmission?

Person-to-person (horizontal), vertical (mother to child), animal-to-person.

What proteins help viruses attach to host cells?

Capsid or envelope proteins that bind to specific cell surface receptors.

How does receptor binding aid viral entry?

Viruses exploit cellular receptors with normal functions, often using carbohydrate components.

What determines viral host specificity?

The presence of specific receptors and host factors (e.g., smallpox vs. influenza A).

What are the main methods of viral entry into host cells?

Direct penetration, membrane fusion, and endocytosis.

Where do DNA viruses typically replicate?

In the nucleus.

Where do RNA viruses typically replicate?

In the cytoplasm.

What are two main mechanisms of virus release from host cells?

Lysis (naked viruses) and budding (enveloped viruses).

How do viruses generate symptoms?

Through cell destruction, altered gene expression, and immune system degradation.

What are the outcomes of viral infections?

Cell death, latency, chronic infection, or transformation (e.g., oncogenesis).

Name two types of oncogenic viruses.

Oncogenic DNA viruses and oncogenic RNA viruses (e.g., Retroviridae).

How do retroviruses integrate into host cells?

Viral RNA is reverse transcribed into DNA and integrates into the host genome.

What is HTLV?

Human T-cell leukemia viruses (HTLV-1 and HTLV-2), associated with oncogenesis.

How are viruses classified?

By replication strategy and host type.

Name four diseases caused by Herpesviridae family viruses.

Cold sores (HSV-1), genital herpes (HSV-2), chickenpox (VZV), mononucleosis (EBV).

What is a notable feature of Herpesviridae infections?

Latency and reactivation (e.g., chickenpox → shingles).

What are common routes of herpes virus transmission?

Through mucosal breaks, eye/genital contact, and skin abrasions.

What can reactivate latent herpes infections?

Physical or psychological stressors (e.g., UV light, menstruation, stress).

Which DNA virus caused smallpox?

Poxviridae.

What is the mortality rate of smallpox historically?

20–60% in adults, over 80% in children.

When was smallpox eradicated globally?

1977, through vaccination.

Name four important RNA viruses.

Poliovirus, Norovirus, Influenza, Rotavirus.

What are key features of poliovirus?

+ssRNA, naked, transmitted via ingestion, vaccine-preventable.

What are early symptoms of poliovirus infection?

Sore throat and nausea.

What severe symptom can poliovirus cause?

Paralysis (in <1% of infections).

What is a retrovirus provirus?

Integrated viral DNA that can remain latent in host genome.

What is a challenge in antiviral drug development?

Identifying virus-specific targets and avoiding resistance.

How do protozoa differ from viruses?

Protozoa are cellular and often cause systemic, long-term infections

Name a faecal-oral protozoan pathogen.

Giardia lamblia (Beaver fever)

What protozoa can damage the cornea and cause encephalitis?

Acanthamoeba and Naegleria

What disease does Trichomonas vaginalis cause in women?

Vaginitis

How is Trichomonas vaginalis transmitted?

Almost exclusively through sexual contact.

What is the reservoir for Toxoplasma gondii?

Wild/domestic mammals and birds; transmission via undercooked meat or contaminated soil.

How can toxoplasmosis affect pregnancy?

It can cross the placenta and infect the fetus.

What disease does Trypanosoma cruzi cause?

Chagas' disease

What is the vector for Trypanosoma cruzi?

Triatoma ('kissing bugs')

What disease does Trypanosoma brucei cause?

African sleeping sickness

What protozoan causes malaria?

Plasmodium species (e.g., P. falciparum, P. vivax)

What is the vector for Trypanosoma brucei?

Tsetse fly