School Science Lessons
Viruses
2025-08-21
(UNBiology9)
Viruses
Contents
DNA Deoxyribonucleic acid
RNA Ribonucleic acid
9.14 Virus list
9.1 Viruses
9.2 Virus classification
9.3 Viruses and viral diseases
9.4 Bacteriophage
9.5 Coronavirus
9.11 Virus diseases of plants
9.12 ToBRFV, New tomato virus, 269/03/2025
9.13 Tobamovirus


9.1. Viruses
Viruses are minute infectious agents whose genomes are composed of DNA or RNA, but not both.
They lack independent metabolism and cannot replicate outside living host cells, so they must infect the cells of other types of organisms to reproduce.
Most viruses are capable of passing through fine filters that retain bacteria, but are not visible through a light microscope.
1. A viruses consists of two parts, genetic material, DNA or RNA, in a coat of protein.
The nucleic acid in the virus contains instructions for the cell to make new viruses.
A virus is a submicroscopic infectious agent that replication inside a cell by using the cell's own biochemical processes.
Viruses cause infected cells to produce progeny viruses.
Retroviruses use the enzyme reverse transcriptase to copy the viral RNA into DNA.
Viruses are not affected by antibiotics.
To transduce a cell is to transfer genetic material from another cell to that cell, another usually by a virus particle or a virus.

9.2 Virus classification
The classification of viruses can be based on the type and arrangement of the genetic material.
The Baltimore classification is based on the viruses nuclreic acid, (DNA or RNA), single or double strand, DNA sense, method of replication.

Group I. dsDNA viruses, Double-strand DNA viruses including:
Oral herpes, herpes zoster (shingles) genital herpes, chickenpox viruses, cold sore, Herpes simplex virus, types 1 and 2 (HSV-1 and HSV-2)
Adenoviruses human adenoids, tonsils, Human Papilloma Virus (HPV) causes dermal warts and genital warts Condylomata acuminata,

Group II. ssDNA viruses, Single-strand DNA viruses include the smallest viruses, (ssDNA = Single-Stranded DNA).

Group III. dsRNA viruses, Double-strand RNA viruses, include viruses responsible for diarrhoea in children.

Group IV. +ssRNA viruses, Positive-strand RNA viruses include influenza, hepatitis C virus (HAV)
Infectious hepatitis from faecal contamination of food and water and possibly milk, shellfish
Hepatitis C virus (HCV) from exchange of body fluid, blood transfusion, sexual contact, shared needles for intravenous drug use
West Nile virus
Dengue virus
MERS, SARS and SARS-COV2 coronoviruses
Rinoviruses, the common cold

Group V. -ssRNA viruses, Negative-strrand RNA viruses viruses include influenza, measles (rubeola)
Mumps infection of salivary glands (paramyxovirus) rabies, Ebola virus, foot-and-mouth disease.

Group VI. ssRNA-RT viruses, Retroviruses, use reverse transcriptase, and include HIV-1 and HIV-2 viruses.
A retrovirus can insert a DNA copy of its RNA genome into the DNA of the host cell.

Group VII. dsDNA-RT viruses, Double-stranded RNA viruses
Rotaviruses cause gastroenteritis in young children.
Bluetongue virus affects cattle and sheep.
Hepatitis B virus (HBV) serum hepatitis from exchange of body fluid, blood transfusion, sexual contact, pregnant mother to baby, shared needles.
Human Immunodeficiency Virus, HIV, and AIDS, is the acquired immune deficiency syndrome.


Infectious agent | Common name | Signs and symptoms
1. Junin virus | Argentine hemorrhagic fever | fever, headache, loss of appetite, vomiting, if left untreated: organ failure
2. BK virus | BK virus infection | usually asymptomatic; fever, difficulty urinating
3. Machupo virus | Bolivian hemorrhagic fever | headache, fever, myalgia, external and internal bleeding, convulsions, tremours
4. Sabiá virus | Brazilian haemorrhagic fever | flushing of face and chest, petechiae, bodily swelling caused by edema, low blood pressure
5. Chlamydia trachomatis | Chlamydia In women | if is not detected by their doctor, approximately half will develop pelvic inflammatory disease (PID)
6. Coxsackie B virus | Coxsackie B virus infection | fever, headache, sore throat, gastrointestinal distress, extreme fatigue as well as chest and muscle pain
7. Cytomegalovirus | Cytomegalovirus infection | fatigue, swollen glands, fever, sore throat, muscle aches
8. Parvovirus B19 | Erythema infectiosum (Fifth disease)
9. Human herpes virus 6 (HHV-6) and human herpes virus 7 (HHV-7) Exanthem subitum (Sixth disease)
10. Enteroviruses, mainly Coxsackie A virus and enterovirus 71 (EV71) Hand, foot and mouth disease (HFMD) | fever, rash, small blisters
11. Herpes simplex virus 1 and 2 (HSV-1 and HSV-2) | Herpes simplex | blisters on genitalia and lips
12. Human papillomavirus (HPV) infection | Warts
13. Human parainfluenza viruses (HPIV) | Human parainfluenza virus infection
14. Human T-lymphotropic virus 1 (HTLV-1) | Human T-lymphotropic virus 1 infection
15. Epstein–Barr virus (EBV) | Epstein–Barr virus infectious mononucleosis (Mono)
16. Orthomyxoviridae species | Influenza (flu) | fever, chills, headaches, muscle pain or aching, a feeling of discomfort, loss of appetite, lack of energy/fatigue,
dry cough, sore or dry throat, hoarse voice, and a stuffy or runny nose.
17. Japanese encephalitis virus | Japanese encephalitis | fever, headache and malaise, cachexia, hemiparesis, convulsions body temperature between 38–41 °C<
18. JC virus | Progressive multifocal leukoencephalopathy | clumsiness, progressive weakness, and visual, speech, and sometimes personality changes

9.3 Viruses and viral diseases

1. Respiratory infections
Rhinovirus, (coronovirus), causes common cold, (Acute viral rhinopharyngitis; Acute coryza), nasal congestion, headache, sneezing, runny nose, sore throat.
Influenza, (orthomyxovirus), (influenza virus A, B, C), causes nasal obstruction, headache, sneezing, chest pain, cough.
Coronavirus disease 2019 (COVID-19), fever, cough, loss of taste and smell
SARS coronavirus causes Severe acute respiratory syndrome (SARS-CoV-2)
Respiratory syncytial virus (RSV) causes Respiratory syncytial virus infection, which may be a mild upper respiratory tract infections (URTI)
or a severe lower respiratory tract infections (LRTI).
Adenovirus causes Adenovirus infection, fever, sore throat, conjunctivitis
Parainfluenza virus infection

2. Digestive system infections
Gastrointestinal viral diseases, spread by ingestion into the digestive tract, cause gastroenteritis.
Norovirus infection, Rotavirus infection, Adenovirus infections, Astrovirus infection, diarrhoea, nausea, vomiting, fever, abdominal pain.
Hepatitis viruses cause liver disease.

3. Eruptive viral diseases
They are rash causing viruses, and spread from skin contact
Varicella zoster virus, (VZV), causes Chickenpox, (and shingles), nausea, loss of appetite, aching muscles, headache, chickenpox rash.
Alphavirus Chikungunya causes Chikungunya, transmitted by Aedes Aegypti mosquito, high fever, severe joint pain, rash.
Fifth disease, caused by parvovirus.
Measles virus | Measles Fever, (rubeola, subacute sclerosing panencephalitis), cough, runny nose, inflamed eyes, rash and Koplik's spots.
Rubella virus | Rubella, (German measles), now regional elimination.
Monkeypox virus | Monkeypox Fever, with headache, muscle pains, shivering, blistering rash, swollen lymph nodes
Variola major or Variola minor viruses | smallpox, which has been eradicated worldwide, but some cultures exist in laboratories.

4. Hepatic viral diseases
These are liver inflammation diseases.
9.7.0 Hepatitis

5. Cutaneous viral diseases These viruses are spread through physical contact.
Warts, Genital warts, Human Papilloma Virus (HPV), Genital warts, (Condyloma acuminata)
Variola major or Variola minor
Varicella zoster virus (VZV) Shingles (Herpes zoster) 9.6 Herpes, genital herpes, genital ulcers
9.5 Herpes, Oral herpes, Genital herpes
Molluscum contagiosum virus (MCV) causes Molluscum contagiosum (MC, small raised, pink lesions with a central dimple).

6. Viral haemorrhagic fevers
Haemorrhagic viral diseases
Crimean-Congo hemorrhagic fever virus causes Crimean-Congo hemorrhagic fever (CCHF) Dengue fever viruses, (DEN-1, DEN-2, DEN-3 and DEN-4) cause Dengue Fever, transmitted by Aedes Aegypti mosquito, high fever, flu-like symptoms,
muscle and joint pains, and a rash, if severe then dengue hemorrhagic fever.
Ebola virus disease from body fluids of infected animals.
Lassa virus causes Lassa fever, partial or complete hearing loss.
Marburg virus causes Marburg Haemorrhagic Fever (MHF), fever, weakness.
Yellow fever virus causes Yellow Fever, from infected mosquitoes.

7. Neurologic viral diseases
Nipah virus causes Nipah virus infection, diarrhoea, vomiting, stomach pain, headache.
Mumps virus, (Paramyxovirus) causes Mumps, fever, headache, malaise, muscle pain, and loss of appetite
Poliovirus caused Poliomyelitis Fever, which attacked motor neurones, paralysis and atrophy of muscles, but now worldwide eradication.
Rabies lyssavirus caused Rabies Fever, infected peripheral nerves then central nervous system, with extreme aversion to water, excessive salivary secretion,
hallucinations, but worldwide elimination in humans and animals.
Viral meningitis, Viral encephalitis
West Nile virus causes West Nile fever, transmitted by mosquitoes, joint pain and skin rash.

8. Congenital virus infections
Cytomegalovirus (CMV) a herpes virus causes congenital CMV, now regional elimination
, Rift Valley fever virus causes Rift Valley fever (RVF), affects grazing animals which may infect humans, causing mild fevers.
9.10 Zika virus

9. Sexually transmitted viruses
9.8.1 HIV/AIDS, weakens the immune system
HPV (Human Paoillomavirus), may cause cervical cancer
Genital herpes, Herpex simplex, HSV-1, HSV-2
Hepatitus B, causes liver inflammation

9.4 Bacteriophage
See diagram 9.3.70: T4 bacteriophage that attacks E. coli.
A bacteriophage or "phage" is a very small virus that infects bacteria.
The T4 bacteriophage infects the bacterium Escherichia coli, (E.coli), found in the human gut.
This infection is used to study viruses and how they infect and replicate inside cells.
T-phages have head, capsid, containing double-stranded DNA genetic material.
The tail of the bacteriophage includes the tail, sheath, base plate and tail fibres, made of different proteins, used to attach itself to the bacterium.
The phage then inserts its own genetic material inside of the host bacterial cell so that it replicates and make more bacteriophages.

9.5 Coronavirus
COVID-19 virus Centres for Disease Control and Prevention
CORONAVIRUS National Institutes of Health
Coronaviruses are a big group of viruses that cause illnesses, e.g. common cold or diseases including SARS (severe acute respiratory syndrome) and MERS.
COVID-19, (Corona Virus Disease 19), is a new strain that has not been previously identified in humans.
The viruses are named for the corona, or crown, of surface proteins that the virus uses to penetrate the cells of its host.
Coronavirus disease 2019
(COVID-19) is an infectious disease caused by the severe acute respiratory syndrome coronavirus 2, (SARS-CoV-2).
The disease had spread globally by 13/03/2020, since 2019, resulting in the 2019–20 coronavirus pandemic.
Common symptoms include fever, cough and shortness of breath.
Muscle pain, sputum production and sore throat are some of the less common symptoms.
While the majority of cases result in mild symptoms, some progress to pneumonia and multi-organ failure.
The case fatality rate is estimated at between 1% and 5%, but varies by age and other health conditions.

"Kill Coronavirus by washing your hands with soap"
Based on article by Palli Thordarson, Professor of Chemistry, University of New South Wales.
Viruses can be active outside the body for hours, even days.
Disinfectants, liquids, wipes, gels and creams containing alcohol are all useful at getting rid of them, but they are not quite as good as normal soap.
Health authorities have been giving us two messages:
1. When you have the virus there are no drugs that can kill it or help you get rid of it.
2. Wash your hands to stop the virus spreading.
Why does soap work so well on the Coronavirus, and indeed most viruses?
Because the virus is a self-assembled nanoparticle in which the weakest link is the lipid (fatty) bilayer.
Soap dissolves the fat membrane and the virus falls apart and dies, or rather, we should say it becomes inactive as viruses aren’t really alive.
Most viruses consist of three key building blocks: RNA, proteins and lipids.
A virus-infected cell makes lots of these building blocks, which then spontaneously self-assemble to form the virus.
There are no strong covalent bonds holding these units together, so you do not necessarily need harsh chemicals to split those units apart.
When an infected cell dies, all these new viruses escape and go on to infect other cells.
Some end up also in the airways of lungs.
When you cough, or especially when you sneeze, tiny droplets from the airways can fly up to 10 metres.
The droplets are thought to be the main Coronavirus carriers and they can go at least two metres.
These tiny droplets end on surfaces and often dry out quickly, but the viruses remain active.
Human skin is an ideal surface for a virus, because it is “organic” and the proteins and fatty acids in the dead cells on the surface interact with the virus.
When you touch, say, a steel surface with a virus particle on it, it will stick to your skin and hence get transferred on to your hands.
If you then touch your face, especially your eyes, nostrils or mouth, you can get infected, and most people touch their face once every two to five minutes.
Washing the virus off with water alone might work, but water is not good at competing with the strong, glue-like interactions between the skin and the virus.
Soapy water is different, because it contains fat-like substances, amphiphiles, some of which are structurally similar to the lipids in the virus membrane.
An amphiphile chemical compound, (Greek amphis, and philia both 'love'), has both hydrophilic (water-loving) and lipophilic (fat-loving) properties.
The soap molecules “compete” with the lipids in the virus membrane, which is similar to how soap also removes normal dirt from the skin.
The soap not only loosens the “glue” between the virus and the skin, but also the Velcro-like interactions that hold the proteins, lipids and RNA in the virus together.
Coronavirus hits ill and disabled people hardest.
Alcohol-based products, including most “disinfectant” products, contain typically 60-80% ethanol, and kill viruses in a similar fashion.
But soap is better, because you only need a fairly small amount of soapy water, which, with rubbing, covers your entire hand easily.
Whereas you need to literally soak the virus in ethanol for a brief moment, and wipes or rubbing a gel on the hands does not guarantee that you soak every corner of the skin on your hands effectively enough.
Soap is the best, but do use alcohol-based sanitisers, when soap is not handy or practical.
5.3.2 Warts
Causative organism: Human papilloma viruses (HPV) usually types 6 & 11
Incubation period: 3 weeks to >12 months.
Most HPV infection is subclinical
Usual testing method: Clinical examination
Common symptoms: Anogenital warts
Likelihood of transmission per unprotected exposure High
Likelihood of long-term sexual partner being infected > 60%
Protective effect of condoms: Moderate
Transmission by oral sex: Rarely of clinical significance
Duration of potential infectivity: Months, probably years if HSV infection is persistent
Important consequences: Psychosexual morbidity
Possibly enhanced HIV transmission
Direct benefit of detection and treatment of contacts: None, unless already symptomatic
How far back to trace Contact tracing not recommended
Usual management of contacts: Counselling
Contact tracing priority: Low and not recommended
The majority of partners are probably already infected subclinically.
Notification: Not notifiable.

9.10 Zika virus
Zika virus Zika fever rash, fever, red or swollen eyes, pain in joints, The Zika virus is on the move and new measures are needed to help to slow it down.
It is a distressing and disturbing infection that may be linked to thousands of babies being born with microcephaly.
It is spreading through the Americas.
Threats from the same virus family are increasing.
Currently, there is no effective treatment or vaccine against the Zika virus
The best way to protect yourself is to avoid being bitten by mosquitos.
The Brazilian Ministry of Health will distribute 500, 000 tests to perform Zika virus diagnostics.
As a result, public laboratories will expand 20 times to assist with this extra surveillance.

9.11 Virus diseases of plants
Viruses may cause yellow patches on leaves and later the plant dies, e.g. in taro and bananas.
These diseases cannot be cured, but if the virus is carried by insects they may be controlled.
The best way to deal with bacterial or virus diseases is to burn the infected plant or part of the plant.
Diseases are carried to plants in four ways:
1. Wind can carry diseases a short distance.
2. Disease can be carried in running water or in the splash of rain drops.
3. Infected plants can pass disease to healthy plants if the plants are touching.
4. Disease can be carried by insect pests that can then infect healthy plants.
Virus diseases include apple mosaic, clover stunt and cymbidium virus of orchids.
Yellow crinkle of papaya and big bud of tomatoes are caused by mycoplasma-like organisms (phytoplasmas).

9.12 ToBRFV, New tomato virus, 19/02/2020
Tobamoviruses include Tobacco Mosaic Virus (TMV) and Tomato Mosaic Virus (ToMV).
ToBRFV can overcome all known genetic resistance in tomato, including the Tm-22 gene.
It can cause severe fruit symptoms on otherwise resistant tomato varieties.
Pepper is another primary host for ToBRFV.
The L genes for resistance to TMV and PMMoV (Pepper mild mottle virus) in pepper currently seem to hold up to ToBRFV.
Peppers without the resistance gene(s) are highly susceptible to the virus.
Transfer of the virus from infected to healthy plants commonly occurs via mechanical means, e.g. touching and manipulation of infected plants.
ToBRFV is similar to other tobamoviruses in that the virus particles are long, symmetrical rods, so it cannot be distinguished by electron microscopy.
Tomato F1 cultivars that are highly resistant (HR) to ToMV and TMV can be severely affected by this new virus. ToBRFV.
The known resistance genes do not protect against ToBRFV, and only preventative crop management and sanitation practices will produce a useful crop.
Some tomato varieties can develop a high virus level without physically expressing symptoms.
Iinfected plants of these varieties can then become a source for spread of ToBRFV infection to healthy tomato plants or susceptible pepper plants.
Seed companies are working on identifying and introducing resistance to the virus in new varieties.
However, but it could take several years, until new resistant varieties are introduced.

9.13 Tobamovirus
Tobamovirus is a genus in the virus family Virgaviridae.
The name "Tobamovirus" comes from the first virus discovered, (Tobacco mosaic virus).
Tobamovirus is a genus of plant viruses with a rigid helical rod containing linear single-stranded RNA.
Tobacco mosaic virus is the type species and is also known as Tobacco mosaic virus group.
Tobamoviruses are a group of viral diseases that cause mottling and damage to important vegetable, fruit, field and ornamental plants.
They occur in Asia, Nigeria, North America, Brazil, and Europe.
They spread by importation of infected plants and plant material including seeds; local spread through plant to plant contact, pruning, harvesting, and clothing.
Many vegetable crops including melons, squash, tomatoes, potatoes, and capsicum are suseptible, but they do not affect human health.
Tobamoviruses are highly infectious and can survive for long periods in plant material, contaminated soil and on equipment surfaces.
Plants infected with tobamoviruses have mosaic-like mottling and discolouration on the leaves and fruit.
The Cucumber green mottle mosaic virus, affects cucurbits, pumpkins, melons and related fruit and vegetables.
Infected plants produce little fruit and, since there is no cure, they must be destroyed.
Tobamoviruses include tomato mottle mosaic virus, zucchini green mottle mosaic virus, cucumber mottle virus and tobacco mosaic virus – potato strain.
Farmers and gardeners should look out for, mosaic-like mottling and discoloration on the leaves, distorted leaves, absence of fruit or distorted fruit.
Importation of infected seed, plants and plant material is the most likely way that tobamoviruses infections can occur.
The viruses can infect some weeds, including prostrate pigweed and creeping cucumber.
One key virus, cucumber green mottle mosaic virus (CGMMV), is under management in some areas of Australia.
Classification
* Bell pepper mosaic virus (BPeMV), Brugmansia mild mottle virus, Cactus mild mottle virus (CMMoV),
* Clitoria yellow mottle virus, Cucumber fruit mottle mosaic virus, Cucumber green mottle mosaic virus (CGMMV)
* Cucumber mottle virus, Frangipani mosaic virus (FrMV), Hibiscus latent Fort Pierce virus (HLFPV)
* Hibiscus latent Singapore virus (HLSV), Kyuri green mottle mosaic virus, Maracuja mosaic virus (MarMV)
* Obuda pepper virus (ObPV), Odontoglossum ringspot virus (ORSV), Paprika mild mottle virus
* Passion fruit mosaic virus, Pepper mild mottle virus (PMMoV), Rattail cactus necrosis-associated virus (RCNaV)
* Rehmannia mosaic virus, Ribgrass mosaic virus (HRV), Sammons's Opuntia virus (SOV)
* Streptocarpus flower break virus, Sunn-hemp mosaic virus (SHMV), Tobacco latent virus
* Tobacco mild green mosaic virus, Tomato brown rugose fruit virus (ToBRFV), Tomato mosaic virus (ToMV)
* Tobacco mosaic virus (T2MV) - (Type species of genus Tobamovirus), Tomato mottle mosaic virus,
* Tropical soda apple mosaic virus, Turnip vein-clearing virus (TVCV), Ullucus mild mottle virus,
* Wasabi mottle virus (WMoV), Yellow tailflower mild mottle virus,
* Youcai mosaic virus (YoMV) aka oilseed rape mosaic virus (ORMV)
* Zucchini green mottle mosaic virus

9.14 Virus list
Humans
Respiratory infections
Digestive system infections
Eruptive viral diseases
Hepatic viral diseases
Cutaneous viral diseases Viral haemorrhagic fevers
Neurologic viral diseases
Congenital virus infections
Sexually transmitted viruses
Plants
Bacteriophage (T type) (host E coli)
Broad bean wilt virus on legumes
Clover stunt virus on legumes
Cucumber mosaic virus
Cymbidium virus of orchids
Infection variegation of Camellia japonica
Iris mosaic virus
Leaf roll of potato virus
Lettuce big vein virus
Lettuce necrotic yellows virus
Potato mosaic virus, Potato Virus X
Rose mosaic
Tobacco mosaic virus
Tomato spotted wilt virus on tomato, capsicum, dahlia, chrysanthemum
Turnip mosaic virus
Woodiness of passion fruit virus

DNA
See diagram DNA10: DNA.
DNA, deoxyribonucleic acid, C15H31N3O13P2, primary genetic material polymer of all cells, usually double-stranded, but can be single-stranded.
DNA has a polysugar-phosphate backbone with projections of purines (adenine and guanine) and pyrimidines (thymine and cytosine), to form a double helix.
The double helix is held together by hydrogen bonds between the purines and pyrimidines, (adenine to thymine and guanine to cytosine).
RNA
Ribonucleic acid (RNA), molecule in most organisms and viruses, usually single-stranded, but can be double-stranded.
RNA is made of nucleotides, ribose sugars attached to nitrogenous bases, (adenine, guanine, uracil, and cytosine), and phosphate groups.
The three main types of RNA involved in protein synthesis are 1. messenger RNA (mRNA), 2. transfer RNA (tRNA), and 3. ribosomal RNA (rRNA).
mRNA is transcribed from DNA and contains the genetic blueprint to make proteins.
rRNA forms ribosomes, which link amino acids together to create polypeptides.
RNA mutations can diseases, e.g. Myotonic dystrophy disease, prostate cancer, fragile X syndrome, and amyotrophic lateral sclerosis (ALS). RNA viruses have very high mutation rates to produce newer variants with higher infectivity or increased resistance to antivirals, and these mutations are heritable.
HIV infections are examples of where the viruses replicate and cause severe disease, even in the presence of drugs.