Viral Diseases Notes

Viral Disease

Virus Structure and Classification

• Viruses cause disease primarily by:

  • Taking over cells, preventing their normal function.

  • Killing cells.

• Millions of cells killed leading to signs and symptoms.

Types of Viral Disease

• Viral diseases can be described as:

  • Acute

  • Subclinical

  • Persistent

  • Latent

Acute Infections

• Characterized by:

  • Short duration

  • Rapid onset

  • Quick resolution

Subclinical Infections

• Share qualities with asymptomatic infections (no signs or symptoms).

• Involve vague feelings of being unwell, but not severe enough to seek medical attention.

• Symptoms may include:

  • Slight fever

  • Enlarged glands

• Individuals recover without fully realizing they had a viral illness.

Antibody Response

• Antibodies (represented as Y-shape) attach to antigens (proteins or lipopolysaccharides on foreign substances).

• Antibody titer: concentration of antibodies in the blood.

  • High antibody titer indicates immunity.

• Previous exposure to an illness results in cells ready to produce antibodies.

  • Antibodies quickly attach to the virus.

Rubella (German Measles)

• Often mild or subclinical in adults.

• Significant danger to pregnant women, especially during the first trimester, causing congenital abnormalities.

• Vaccination is crucial.

Cytomegalovirus

• Similar risks to rubella during pregnancy.

• No available vaccine.

• Antibody measurements can indicate prior exposure in pregnant women.

Antibody Timeline

• Different types of antibodies appear at different times after exposure.

  • IgM: increases ~7 days after exposure, peaks, then declines after ~3 weeks

  • IgG: grows after IgM, indicating past exposure. Measuring IgG tells the presence of rubella in the trimester.

• Graph showing the levels of IgM and IgG antibodies over time:

Subclinical Viral Illnesses

• Examples include:

  • Polio

  • Glandular fever

  • Hepatitis B and C

• Majority of viruses can be subclinical.

Self-Limiting Viruses

• Acute lytic infections (e.g., common cold) resolve on their own.

Persistent Viral Infections

• Viruses persist in the body for extended periods.

• Classified as:

  • Latent

  • Slow

  • Chronic

Viral Infections that Cause Cancer

• Virus can alter DNA, leading to uncontrolled cell reproduction (tumor).

• Neoplasia: viruses change the cell multiplication slightly, creating a wart. The wart grows uncontrollably, becomes cancer.

• Viruses introduce genes into cells, altering gene function.

Latent Viral Infections

• Virus particles remain present in cells for years or decades.

• Herpes varicella (chickenpox) example:

  • Initial chickenpox infection in childhood.

  • Reactivation as shingles in adulthood.

• Many herpes viruses and HIV can establish latency.

• Initial disease appears as an acute lytic infection.

• Viral particles hide in cells, often nerve cells, which are less accessible to the immune system.

• Reactivation occurs during stress, illness, or weakened immunity.

Implications for Nurses

• Hospitalized patients are often stressed, unwell, and immunocompromised.

• Latent viral infections, such as shingles, may reactivate.

Herpes Simplex Virus

• Causes cold sores.

• Dormant in nerve cells around the mouth.

• Reactivation triggered by sunlight, stress, or colds.

• Spread by physical contact.

Varicella Zoster Virus

• Causes chickenpox and shingles. Remains in nerve that comes out of the spine and goes to the chest.

• Chickenpox in childhood, remains dormant, reactivates as shingles.

Epstein Barr Virus

• Causes glandular fever.

• Exists in immune cells.

Reactivation of Latent Viruses

• Common in immunocompromised patients, elderly individuals, and those on immunosuppressants.

Shingles Schematic

• Latent viruses (blue spheres) reside in nerve cells.

• Weakened immune system activates the virus.

• Virus travels along the nerve, causing burning sensation and sensitivity.

• Blisters develop, similar to chickenpox, filled with clear fluid that becomes purulent.

• Blisters crust over and heal.

• Nerve damage can result in ongoing pain (postherpetic neuralgia).

Slow Viral Infections

• Virus persists, causing different symptoms from the original disease.

• Measles example:

  • Subacute sclerosing panencephalitis (SSPE): brain damage caused by measles virus.
    Virus particles lodge in the brain and activate about 6-8 years after initial infection, deteriorating the brain over 2 years until the virus kills the host

Chronic Viral Infections

• Virus remains in the host with continuous low-level viral production.

• Virus particles detectable in blood or feces.

• Carrier state: individuals have no symptoms but are infectious.

• Classic example: Hepatitis B.

  • Acute infection can lead to mild/subclinical disease, then chronic stage.

  • Infants have a 90% risk of becoming carriers if infected.

  • Adults have a 10% risk of becoming carriers if infected.

Risks of Carrier State

• Spread of disease to others.

• Risk of long-term liver damage.

Viruses and Cancer

• Possible link between viruses and many cancers.

• Viruses alter DNA, leading to uncontrolled cell reproduction (tumor).

Mechanisms:

• Viruses change cell multiplication (neoplasia, e.g., warts).

• Viruses introduce genes into cells, altering gene function.

Examples of Virus-Induced Cancers:

• Adult T-cell leukemia (human T-cell leukemia lymphoma virus).

• Skin carcinomas, genital carcinomas (human papillomavirus/HPV; vaccine available).

• Kaposi's sarcoma (human herpesvirus; common in HIV patients).

• Liver cancer (hepatocellular carcinoma; hepatitis B and C).

• Nasopharyngeal cancer (Epstein-Barr virus/EBV).

• Burkitt's lymphoma (Epstein-Barr virus/EBV; swelling in glands).

Body's Response to Viral Infections

• Depends on virus type and individual susceptibility.

• Viruses spread via blood or lymphatic system.

• Early stages: virus numbers increase, virions found in plasma or blood cells.

• Infected cells release cytokines, specifically interferon.

Interferon

• Acts directly on uninfected cells, preventing viral replication.

• Triggers immune response.

Immune Response

• Activation of T cells to destroy infected cells (cell-mediated immunity).

• Activation of B lymphocytes to produce antibodies (humoral response).

• Antibodies neutralize free viral particles.

• Development of memory T and B cells for protection against reinfection.

Symptoms of Viral Disease

• Result from the body's immune response, not directly from the virus.

• Include fever, aches, swollen glands, malaise, headache, and muscle aches.

Diagram showing the immune system and the virus.
Exposed to stimulus -

1. activated cytotoxic T cell --> kills infected virus

2. activated T helper cells --> stimulates the B lymphocytes --> releases antibodies to eliminate virus.

Diagram

• Influenza virus stimulates T cell response.

• Cytotoxic T cells directly destroy infected cells.

• T helper cells stimulate B lymphocytes.

• B lymphocytes produce antibodies to eliminate the virus.

• Process leads to symptoms of viral disease.

• Diagram briefly outlines the immune system combating a viral illness.

Treatment of Viral Illness

• Limited treatment options available.

• Focus on maximizing immune response:

  • Rest.

  • Hydration.

  • Nutritious diet.

• Panadol (acetaminophen) provides relief from muscle aches and reduces fever (antipyretic).

  • It's a balancing act to reduce discomfort but may need to prolong the fever.

• Recovery depends on effective antibodies and cytotoxic T cells.

Immune System Considerations

• Immune system less effective in the elderly and very young.

• Viral illnesses like mumps and chickenpox are often worse in adults.

• Hepatitis E is associated with maternal mortality.

Viral Immune Evasion

• Viruses evade the immune system by:

  • Hiding inside infected cells.

  • Changing appearance (e.g., influenza).

  • Becoming latent (dormant).

  • Manipulating the immune response (e.g., HIV destroying T cells).

  • HIV hides in macrophages

Spread of Viral Diseases

• Complete viral particles (virions) are shed by the infected host.

• Most viruses don't survive long outside living cells.

Transmission Requires:

*Direct transfer.
*Close contact.
*Transmission via an insect.

Infectious Period

• Varies during infection.

• Highest number of particles shed just before feeling sick (prodromal phase).

• Explains epidemics: individuals spread the disease before realizing they are ill.

Virus Survival Outside the Body

• Depends on:

  • Whether it's enveloped (survives less long) or naked (survives longer).

  • Number of viruses shed.

  • Temperature (hotter = less survival).

  • Exposure to sunlight (UV light).

Examples of Virus Survival

• Hepatitis A: can survive outside the body for months.

• Hepatitis B: can survive for about 7 days.

• Respiratory syncytial virus (RSV): survives on worktops for ~6 hours, clothing/tissue for ~30-40 minutes, and skin for ~20 minutes.

• Coronaviruses (including COVID-19): can remain infectious on surfaces for up to 9 days at room temperature; inactivated by temperatures above 27-30°C and lipid-destroying substances like alcohol.

Viral Transmission Routes

• Airborne transmission:

  • Problematic due to difficulty in controlling spread.

• Fecal-oral transmission:

  • Associated with poor hand hygiene.

  • Causes hepatitis A, rotavirus, enteroviruses, and noroviruses.

  • Rotavirus -> severe dehydration in children.

  • Food poisonings (noroviruses).

  • Viral shedding continues after symptoms disappear.

  • No immune system response.

• Body fluids:

  • Breast milk, semen, blood, saliva.

• Vectors:

  • Insects (typically mosquitoes) and mammals transmit the viruses.

Vectors: Arthropod Borne Viruses

• Affects: time and ambient temperature.

• 80 affect: humans.

• Requires:

  • Infected individuals.

  • Favorable breeding conditions for mosquitoes.

  • Specific type of mosquito.

Mosquito Control

• Poisoning.

• Preventing.

• Removing breeding areas.

Common Vectors Transmitted Viruses in Australia

• Ross River Fever

• Murray Valley encephalitis

• palmer forest fever

• dengue fever

Consumption of infected animal products

• Cooking the meat kills the virus, spread bacteria though not viruses.

Damage to the Unborn Fetus

• viruses have teratogenic effects

  • German Measles

  • Cytomegalovirus -> congenital effects (heart defects, cataract stiffness and damage to the brain

  • Mother to child = vertical transmission (via body fluids and blood).

Examples:

• Hepatitis B: 90% chance of transmission if untreated.

• HIV: 90% chance of transmission if untreated.

• Hepatitis C

  • Hepatitis B: Mothers given antibodies against Hepatitis B, and child given a course of vaccine.

• Herpes simplex: contracted during birth which damages Childs eyes and brain and can be fatal.

• Cesarean section to avoid exposure of baby to genital tract

Prevention

• Inactivating viruses by changing environmental conditions, such as heat or alkaline solutions.

• Chlorhexidine, ineffective against viruses.

Diagnosis of Viral Infections

• Signs and symptoms:

  • Rash

  • Fever

  • Aches and pains

• Treatment:

  • Panadol

  • Fluids

• early diagnosis to prevent the spread

• COVID tests --> PCR Test to raise the DNA to detectable levels.

Diagnostic Techniques:

• Immunofluorescence.

• DNA test.

• Antibodies in blood:

  • IgM (recent infection).

  • IgG (past infection).

• Viral cultures (difficult and expensive).

Treatment

• Primarily symptomatic:

  • Rest

  • Fluids

  • Analgesia

• limited antiviral drugs due to harming the host.

AZT or Ziduvidine is an example.

Other antiviral treatments

• Acyclovir another nucleoside analog.

• Drugs such as interferons (not great effect).

Drugs are limited for treatments and has a reasonable risk of effects