Viruses - Part 2

Viruses Causing Glandular Enlargement

• MUMPS
  • Childhood disease characterized by bilateral inflammation of parotid glands.
  • Many infections are asymptomatic (inapparent).
  • Complications: meningitis, orchitis (may lead to sterility), and ovaritis.
  • Epidemiology: Spread through salivary and respiratory secretions with an incubation period of 18-21 days.
  • Prevention: MMR vaccine (live, attenuated).

Infectious Mononucleosis (Epstein-Barr Virus)

• Overview:
  • Part of the Herpes virus family.
  • Typically a mild disease, but can be prolonged and debilitating in children and young adults.
  • Transmission: Primarily through saliva, often termed the "kissing disease."
  • Symptoms:
  • Lymphadenopathy
  • Fever
  • Sore throat
  • Presence of atypical lymphocytes
  • Enlargement of liver and spleen
  • Latent Virus: Can lead to chronic disease (rare) or asymptomatic shedding (common) throughout the host's lifetime.
  • Diagnosis: Blood tests indicating atypical lymphocytes; Monospot Test detects RBC agglutination; presence of EBV antigens.
  • Vaccine: No vaccine available.

Cytomegalovirus (CMV)

• Overview:
  • Part of the herpes family; often asymptomatic and latent but can be dangerous in specific populations.
  • At-Risk Groups:
  • Pregnant women: Risk of neonatal infection leading to jaundice, enlarged liver/spleen, intellectual deficiency, and motor disorders.
  • Transplant patients: Can lead to transplant rejection.
  • AIDS/immunocompromised patients: Risk of frequent infections, GI tract ulceration, and retinitis.
  • Diagnosis:
  • Isolation of the virus (urine, blood, organ biopsies).
  • Faster methods: CMV antigen detection, DNA hybridization, PCR in leucocytes.
  • Serological screening for donor and recipient compatibility pre-transplant.
  • Treatment: Antivirals.
  • Prevention:
  • Matching CMV immune status in transplants, preventive antiviral administration, and universal precautions to avoid transmission.
  • No vaccine available.

Hepatitis Viruses

• Definition: Hepatitis refers to inflammation of the liver characterized by malaise, fatigue, nausea, loss of appetite, and jaundice.
• Common Types: Hep A and B are most common and well-characterized; Hepatitis C, E, and G are less common.
• Diagnosis: Usually serological.

Hepatitis A

• Demographics: Mainly affects children and young adults.
• Epidemiology:
  • Transmitted via fecal-oral route.
  • Incubation period: 15-50 days.
  • Stools can be infectious 2-3 weeks before symptoms develop.
  • Generally mild or asymptomatic in children; no chronic hepatitis cases.
  • Immunity is lifelong.
• Diagnosis:
  • Clinical suspicion leads to detection of IgM antibodies.
  • Detection of IgG indicates immunity (important for travelers).
• Prevention:
  • Vaccine recommended for high-risk populations.
  • Administering γ-globulin after exposure for preventive care.

Hepatitis B

• Affected Population: Sporadic cases in all ages.
• Epidemiology:
  • Transmission primarily through contaminated blood, body fluids (saliva, urine, semen).
  • Average incubation period: 90 days; patient infectious 30-60 days prior to symptom onset.
• Clinical Features:
  • More severe than Hepatitis A.
  • Risks for chronic hepatitis and carrier state.
• Diagnosis:
  • Blood test for HepB surface antigen (HBsAg).
  • Antibodies signify markers of infection and immunity, typically appearing several months after onset.
• Prevention:
  • Universal precautions for blood handling.
  • Proper handling of needles and vaccination.
• Post-exposure prophylaxis: HepB immunoglobulins.

Hepatitis C

• Epidemiology:
  • Transmitted through blood and sexual contact.
  • Initially presents as mild disease but commonly progresses to chronic hepatitis.
• Diagnosis: Primarily serological.
• Prevention: Same precautions as HepB.
• Treatment:
  • Epclusa (sofosbuvir-velpatasvir) shows promise in treatment.

Hepatitis Delta Agent

• Epidemiology:
  • Blood and sexual transmission; considered a "viroid" as it relies on HepB for replication.
  • Increases severity of HepB infection.
• Diagnosis: Serological.
• Prevention: Vaccination against HepB.

Hepatitis E

• Transmission: Fecal-oral route; incubation period 15-50 days.
• Symptoms: Similar to Hep A but with a notably high mortality rate (20%) in pregnant women.
• Prevalence: Endemic in regions including India, Pakistan, Nepal, Burma, North Africa, and Mexico.

Hepatitis G

• Epidemiology:
  • Blood and sexual transmission; incubation 14-180 days.
  • Typically mild without jaundice but can lead to chronic hepatitis.
• Diagnosis: Detection of viral DNA via PCR or other molecular methods.
• Prevention: No vaccine available.

Yellow Fever Virus

• Nature: A hemorrhagic fever virus associated with hepatitis.
• Epidemiology: Endemic in Africa, South America, and the Caribbean, with mortality rates up to 50%.
• Transmission: Spread through mosquito bites.
• Prevention: Live attenuated vaccine for travelers in endemic areas.

CNS Viruses - Overview

• Clinical Manifestations:
  • Aseptic meningitis
  • Encephalitis
  • Meningo-encephalitis
  • Poliomyelitis
  • Slow progressive and persistent infections.

Diagnosis of CNS Viruses

• Always exclude bacterial or fungal infections prior to testing.
• Testing Methods:
  • Lumbar puncture (four sites).
  • Other specimens: blood, urine, aspirate, throat swabs, stool, sera.

CNS Viruses with Human Reservoir

• Often an extension of other primary infections:
  • Mumps: Can lead to aseptic meningitis, primarily in children.
  • Enteroviruses: Aseptically causes meningitis in infants/children.
  • Herpes Simplex Virus: Rarely causes herpetic encephalitis in young adults; also linked to meningo-encephalitis in neonates and young adults.
  • Vaccinations available for mumps, measles, and polio.

CNS Viruses with Animal Reservoir

• Human infections are rare.
• Examples:
  • Arboviruses: Over 200 types, primarily in tropical areas, often leading to encephalitis (e.g., West Nile virus).
  • Rabies Virus: Leads to fatal acute encephalitis; transmitted via saliva; long incubation (30-60 days).
  • Prevention: Active and passive immunization with rabies vaccine; vaccination of wildlife and pets.

HIV and AIDS

• Description: Severe immunosuppressive condition, often fatal. Increases susceptibility to opportunistic infections and cancers.
• Mechanism: HIV depletes helper T-cells, significantly weakening the host’s immune response. Frequent antigenic changes complicate treatment and prevention.

HIV Transmission & Pathogenesis

• Inactivation: Virus often protected by residing within host cells, making it resistant to external disinfectants.
• Modes of Transmission:
  • Sexual contact
  • Blood and blood products
  • Congenital transmission
  • Organ transplants
  • Sperm donation
• Disease Progression: Characterized by a lengthy asymptomatic phase that increases the spread of the disease; cytocidal action against helper T4 cells leads to AIDS as the immune status declines.

HIV Structure and Replication

• HIV-1 Virion Structure:
  • Components: gp120, gp41, RNA genome, capsid, lipid membrane, matrix proteins.
• Replication Cycle: Involves reverse transcription of viral RNA into DNA, integration into host DNA, and ultimately budding of new virions.

HIV Clinical Features and Diagnosis

• Incubation Period: 6 months to several years; can progress to AIDS-related complex (ARC).
• Terminal Stage Symptoms: Patients may develop neurological issues and are susceptible to numerous opportunistic infections.
• Lab Diagnosis: Serology-based testing; seropositivity may take months; isolation of virus from various biological fluids (e.g., blood, semen).

HIV Prevention

• Measures:
  • Universal precautions for healthcare workers.
  • Screening of blood, organ and semen donors.
  • Heat inactivation of plasma (particularly for hemophiliac patients).
  • Sexual education and drug user education.
  • Pregnant women at risk should be tested.
  • No vaccine currently available, but ongoing research to develop one.

HIV Treatment

• Treatment Options:
  • Various treatment modalities exist, but the most effective is a combination therapy (HAART) involving:
  • Protease inhibitors (block viral maturation).
  • Reverse transcriptase inhibitors (stop viral replication).
  • Treatment can lead to significant side effects and is expensive, presenting challenges for implementation in developing countries.