Viruses and Protozoa

Viruses

• Most common cause of illness

  • Primary & secondary infections

  • Overlapping symptoms → need for detailed diagnostics

  • Multiple transmission routes:

    • Person to person (horizontal)

    • Mother to child

    • Animal to person

• Viruses are obligate intracellular parasites

  • Do not grow independently

  • Only reproduce in host cells

  • Depend on host metabolism

Attachment

• Viral proteins (capsid/envelope) bind to specific host receptors

  • Image: Viral Attachment 📷 Image 2

• Receptors normally have other cellular functions

• Viral receptors may bind to carbohydrate components

Specificity

• Highly host specific:

  • Smallpox virus (Human specialist)

• Broad host range:

  • Influenza A → mammals and birds

• Immunization relevance

Entry & Uncoating

• Direct penetration

• Fusion with host membrane

• Stimulation of endocytosis (both enveloped and non-enveloped)

  • Image: Virus Entry Mechanisms 📷 Image 4

Synthesis & Assembly

• Viral protein synthesis in cytoplasm

• Genome replication:

  • DNA viruses → nucleus

  • RNA viruses → cytoplasm

• Assembly of new virus particles

Release / Exit

• Lysis:

  • Naked & pox viruses rupture host cell

  • Host cell usually dies

• Budding:

  • Enveloped viruses

  • Host cell may survive

  • Image: Budding vs Lysis 📷 Image 6

Symptom Generation

• Host cell destruction

• Gene expression changes

• Immune system degradation

• Viral evasion from immune detection

🔄 Outcomes of Infection

• Possible outcomes visualized in diagram

  • Image: Infection Outcomes 📷 Image 7

🧬 Oncogenic Viruses

• DNA Viruses:

  • Adenoviridae, Herpesviridae, Poxviridae, Papovaviridae, Hepadnaviridae

• RNA Viruses:

  • Retroviridae (e.g., HTLV-1, HTLV-2)

  • RNA transcribed to DNA, integrates into host DNA

🧪 Classification

• Based on replication strategy and host type

• Image: Baltimore Classification 📷 Image 9

🧬 DNA Viruses of Importance

• Herpesviridae:

  • HSV-1, HSV-2, VZV (HHV-3), CMV (HHV-5), HHV-6, HHV-7, EBV (HHV-4), KSHV (HHV-8)

  • Common features:

    • Latency & reactivation

    • Often asymptomatic

    • Age-specific infection patterns

    • 90% adults infected

  • Image: Herpesviridae Summary 📷 Image 11

• Poxviridae:

  • Smallpox, Cowpox, Monkeypox

  • High historical mortality

  • Eradicated in 1977

  • Image: Smallpox Historical Impact 📷 Image 13

🧬 RNA Viruses

• Poliovirus, Norovirus, Influenza, Rotavirus, Hantavirus, Ebola, Coronaviruses

• Image: RNA Viruses & Structures 📷 Image 14

🧠 Poliovirus

• +ve RNA, naked virus

• Transmitted by ingestion

• Can enter CNS → paralysis

• Preventable by vaccination

  • Image: Poliovirus Pathogenesis 📷 Image 15

🔁 Retroviruses

• DNA integrates into host genome

• Transcribed to mRNA

• May persist latently as provirus

🎯 Antiviral Targets

• Interference with viral life cycle

• Image: Antiviral Targets Diagram 📷 Image 16

• Challenges:

  • Virus-specific targeting

  • Drug resistance

🦠 Protozoa

🧬 General Characteristics

• Intracellular parasites

• Cause significant morbidity/mortality

• May behave as parasites or pathogens

  • Insect-borne → systemic, hard to treat

  • Faecal-oral → short-term diseases

💩 Faecal-Oral Protozoa

• Giardia

  • "Beaver Fever"

• Amoebic Dysentery

• Cryptosporidium

🧠 Acanthamoeba & Naegleria

• Acanthamoeba → corneal damage, fatal encephalitis

• Naegleria → brain infection

  • Image: Brain Scan Naegleria 📷 Image 19

👩‍⚕ Trichomonas vaginalis

• Most common protozoal STD in industrialized nations

• Lives in genitourinary tract

• Transmitted via sex

• Causes vaginitis in women

• Often asymptomatic in men

  • Image: Trichomonas Microscopy 📷 Image 18

🐱 Toxoplasma gondii

• Causes toxoplasmosis

• Wide animal reservoir

• Transmission:

  • Undercooked meat

  • Inhalation/ingestion of contaminated soil

  • Can cross placenta → fetal infection

  • Image: Toxoplasmosis Transmission 📷 Image 21

🪳 Trypanosoma cruzi

• Chagas’ disease

• Reservoir: armadillos, opossums

• Transmitted by Triatoma (“kissing bugs”)

• Causes parasite-induced heart disease

🦟 Trypanosoma brucei

• African sleeping sickness

• Vector: Tsetse fly

• Three-stage illness

• Characterized by cyclical waves

• Habitat control reduces cases

  • Image: Trypanosoma brucei Life Cycle 📷 Image 22

🐶 Leishmania

• Causes leishmaniasis

• Reservoir: dogs, rodents

• Vector: Sandflies

🦟 Plasmodium

• Malaria causative agent

• Four species: P. falciparum, P. vivax, P. ovale, P. malariae

• Transmitted via mosquitoes

• Life cycle has 3 prominent stages

  • Image: Plasmodium Life Cycle 📷 Image 23