Viruses Honor

Nature Study

Requirements

1. What does the word virus mean? Explain why there is a controversy over whether it is a living being or not.

   Answer: Virus comes from the Latin virus = "poison" or "toxin". There is controversy because viruses have characteristics of living beings (genetic material, they evolve, they reproduce) and of non-living things (no cells, no metabolism of their own, they depend on a host to replicate). Without a host cell, a virus is just an inert chemical structure. Many scientists consider it an extreme parasite, not life. — The definition of life requires cells, metabolism, autonomous reproduction; a virus has only genetic material (DNA or RNA) and a protein capsule; discovered in 1892 by Ivanovsky in tobacco; the "living or non-living" debate appears in every biology book since Lwoff (1957); SARS-CoV-2 is a recent example that renewed the scientific debate, in effect today.

2. Cite the distinctive characteristics of viruses and why they are not included in any kingdom.

   Answer: Viruses are acellular (without cells), they have only genetic material (DNA or RNA) wrapped in a protein capsule (capsid), they are obligate parasites (they need a host cell to replicate) and they have no metabolism of their own. Because of these unique characteristics — they do not live, do not feed, do not respond to stimuli — they do not fit into the 5 biological kingdoms. — The 5 classic kingdoms (Monera, Protista, Fungi, Plantae and Animalia) require the being to have cells — and viruses have no cell at all. That is why they are left out of the kingdoms; some scientists have even proposed a separate group just for them, but there is no consensus classification. The Covid-19 pandemic (SARS-CoV-2) reignited the debate over whether viruses should or should not be considered living beings.

3. Cite some morphological forms of viruses and an example of each.

   Answer: Forms: icosahedral (a 20-faced polyhedron — adenovirus, herpes), helical (spiral — the tobacco mosaic virus TMV, rabies), enveloped (with an external lipid membrane — influenza flu, HIV) and complex (a mixture of forms — the T4 bacteriophage that looks like a spaceship, smallpox). Each morphology helps with entering and leaving the host cell in different ways. — The icosahedral capsid is the most common (efficient in volume); HIV and the flu have an envelope that facilitates fusion with the cell; the T4 bacteriophage attacks bacteria with its contractile tail structure; morphological classification formalized by Lwoff and Tournier in 1962 — the basis of modern virology taught at Brazil's Fiocruz, in effect today.

4. Explain the importance of vaccines in combating viruses. How do they work?

   Answer: Vaccines are fundamental — they have prevented millions of deaths from smallpox, measles, polio. They work by presenting an antigen (a weakened or killed virus, a fragment or messenger RNA) to the immune system without causing disease. The body produces antibodies and memory cells — when the real virus attacks later, there is a quick and efficient response. Individual and collective (herd) immunization. — Smallpox was eradicated in 1980 thanks to the vaccine; mRNA vaccines (Pfizer, Moderna) revolutionized things with COVID; herd immunity protects those who cannot be vaccinated (allergic, immunocompromised people); SUS offers 19 free vaccines in the national schedule; the Sabin Vaccine Institute estimates 4 million lives saved per year worldwide, in effect.

5. Describe the forms of viral reproduction and how the genetic differentiation that promotes viral mutations and resistance can occur.

   Answer: Viruses reproduce in a lytic cycle (they enter the cell, replicate, destroy it) or a lysogenic cycle (they integrate viral DNA into the cell's DNA, remaining dormant). Mutations occur from copying errors of the viral polymerase (especially in RNA viruses such as HIV, the flu), and from genetic recombination between different viruses. Mutations can generate variants that are more infectious or resistant to treatment. — HIV mutates 1 million times more than humans; influenza mutates seasonally (hence the annual vaccine); SARS-CoV-2 generated the Alpha, Delta, Omicron variants through mutation; recombination occurs when 2 viruses infect the same cell (such as avian + swine flu = the 2009 pandemic); the cycles described by Lwoff (Nobel 1965) are a virological basis, in effect.

6. Has any viral disease ever been eradicated? Why is the treatment of viral diseases so difficult?

   Answer: Yes, smallpox was eradicated in 1980 (the only eradicated human viral disease). Polio is close to eradication. Viral treatment is difficult because the virus invades cells and uses the cellular machinery to replicate — attacking the virus can damage the cell. Antibiotics do not work (they are for bacteria). Antivirals exist but are limited; vaccines are the best preventive strategy. — Smallpox eradicated by the WHO after a 200-year campaign started by Edward Jenner (1796); polio fell from 350 thousand cases in 1988 to fewer than 50 in 2023; antivirals such as acyclovir (herpes) and oseltamivir (flu) are exceptions; HIV has no cure but is controllable; the WHO global standard applied in Brazilian public health, in effect today.

7. Differentiate the following exanthematous (rash) diseases:
   • Rubella
   • Measles
   • Chickenpox (Varicella)

   Answer: Exanthematous diseases are those that cause an exanthem, that is, red spots/eruptions spread over the skin. 1) Rubella: caused by the Rubivirus. It presents mild and more discreet red spots, low fever and swollen lymph nodes, mainly on the neck and behind the ears. It is especially dangerous in pregnant women, as it can cause malformation in the baby. Preventable by the MMR vaccine. 2) Measles: caused by the Morbillivirus. It causes high fever, red spots that spread over the body (starting on the face) and the characteristic white spots inside the mouth (Koplik's spots), in addition to coughing and conjunctivitis. It is highly contagious and is also prevented by the MMR vaccine. 3) Chickenpox (Varicella): caused by the Varicella-zoster virus. It is characterized by little blisters (vesicles) filled with fluid that itch a lot and appear all over the body, in different stages at the same time, accompanied by fever. It has its own vaccine. — The MMR vaccine prevents measles + rubella + mumps (SUS double dose); chickenpox has an optional vaccine (SUS); congenital rubella causes fetal malformations (rubella syndrome); HHV-6 infects 95% of people by age 2; the Ministry of Health classification standard applied in Brazilian pediatrics, in effect today.

8. Choose three of the viral diseases below and describe the form of contagion, symptoms and prevention:
   • Rabies
   • Herpes
   • AIDS
   • Mumps
   • Poliomyelitis
   • Meningitis
   • Hepatitis
   • Dengue

   Answer: Choosing three diseases from the list — Dengue, Rabies and AIDS: 1) Dengue: contagion through the bite of an infected Aedes aegypti mosquito. Symptoms — high fever, headache, pain behind the eyes, body aches and red spots on the skin. Prevention — eliminate sources of standing water (where the mosquito breeds), use repellent and screens, and keep water tanks covered. 2) Rabies: contagion through a bite, scratch or lick on a wound made by an infected animal (dogs, cats, bats). Symptoms — fever, agitation, difficulty swallowing, intense salivation and behavioral changes; it is almost always fatal once symptoms appear. Prevention — vaccinate dogs and cats, avoid contact with unknown or wild animals and go to a health center immediately after any bite (post-exposure vaccine). 3) AIDS: caused by the HIV virus; contagion occurs through unprotected sexual intercourse, contact with contaminated blood (shared needles/syringes) and from mother to baby during pregnancy, childbirth or breastfeeding. Symptoms — progressive weakening of the immune system, leaving the body vulnerable to opportunistic infections, weight loss, fever and fatigue. Prevention — use of a condom, not sharing sharp objects and prenatal care; there is treatment with antiretrovirals that controls the disease. — Dengue kills 1,500 Brazilians/year (3 million cases in 2024); COVID-19 caused 700 thousand deaths in Brazil 2020-2023; seasonal flu kills 30 thousand/year worldwide; a pattern of common viral diseases applied in Brazilian public health campaigns by the Ministry of Health throughout the national territory, in effect today.

9. Differentiate the flu and the common cold. Why does the Influenza virus cause periodic epidemics (such as the Spanish flu, avian flu, swine flu (H1N1), etc.).

   Answer: Flu (Influenza): high fever (>38°C), intense muscle pain, fatigue, lasts 5-7 days, can have complications. Common cold (rhinovirus, etc.): runny nose, sneezing, mild sore throat, no high fever, lasts 3-5 days. Influenza causes epidemics because it has a high mutation rate (antigenic drift and shift) — the vaccine needs to be updated annually to keep up with new variants. — The Spanish flu (1918) killed 50 million; the H5N1 avian flu still worries the WHO; antigenic drift is gradual mutation; shift is recombination between human and animal viruses (pigs are mixers); the seasonal vaccine is updated with 4 predicted strains; the CDC and Ministry of Health standard for Brazilian campaigns, in effect today.

10. What is the difference between a virus and a prion? Cite a disease caused by a prion.

    Answer: A virus has genetic material (DNA or RNA) and a protein capsule; it replicates by invading a cell. A prion is just a misfolded protein — it has no genetic material. A prion contaminates by forcing other normal proteins to misfold, causing fatal neurological degeneration. Prion diseases: mad cow disease (BSE) in cattle, Creutzfeldt-Jakob (CJD) in humans, kuru (cannibalism). — The prion was discovered by Stanley Prusiner in 1982 (Nobel 1997); it contradicts the central dogma of biology (it does not use DNA); BSE caused a global crisis in the 1990s; CJD affects 1 in a million per year; resistant to heat and disinfectants — a normal autoclave does not destroy it; the Anvisa standard for spongiform encephalopathy applied in Brazil, in effect today.

11. Make a brief report on a viral pandemic and the impact it caused on the world.

    Answer: Choose a pandemic (Spanish flu 1918, AIDS 1981, COVID-19 2020) and describe: the causative virus, the year it started, the affected countries, the number of cases and deaths, the social impact (lockdowns, closed schools, the economy), the resulting scientific advances (vaccines, treatments), the lessons learned and the permanent changes (public health, remote work, online education). — The Spanish flu killed 50 million; AIDS has already killed 40 million; COVID-19 killed 7 million officially; each pandemic accelerated science (mRNA vaccines in months), the economy lost trillions (IMF 2020); remote work jumped from 5% to 40% in the US during COVID — a historical medical study pattern applied in Brazilian schools, in effect today.