Viral Diseases: DNA Viruses Classification

Viral Diseases and Oncogenic Viruses

DNA Viruses Classification

• DNA viruses can be classified based on their DNA structure and presence of an envelope.
• ssDNA, naked viruses include Parvo.
• Partially dsDNA, enveloped viruses include Hepadna.
• dsDNA, naked viruses include Adeno and Papova.
• dsDNA, enveloped viruses include Herpes and Pox, with Pox having complex symmetry.

Poxviridae (Poxvirus)

• Poxviridae are the largest DNA viruses.
• They have double-stranded DNA and complex symmetry.
• Transmission typically occurs through direct contact.
• Poxviruses can cause skin lesions, including macules, papules, and pustules (pocks or pox).
• Molluscum contagiosum is another disease caused by poxviruses, also sexually transmitted.
• Orthopoxvirus includes Variola which causes Smallpox (now eliminated), and its primary host is humans.
• Orthopoxvirus vaccinia primary host is humans and causes localized lesion; used for smallpox vaccination.
• Orthopoxvirus includes Monkeypox, which primarily affects rodents and monkeys, can cause generalized disease in humans.
• Parapoxvirus includes Orf, which primarily affects sheep and is zoonotic, causing localized lesions in humans.
• Molluscipoxvirus includes Molluscum contagiosum, which primarily affects humans and causes benign skin nodules.
• Smallpox is a disease caused by the Orthopoxvirus Variola.
• Smallpox (variola major) has a fatality rate 10-50%.
• Smallpox (variola minor) has a fatality rate less than 1%.
• Smallpox progresses through stages: macules to papules to vesicles to pustules, leaving permanent marks.
• Smallpox was eradicated in 1978.
• Monkeypox is transmitted to humans via infected animal bodily fluids or bites, and through human to human transition.
• Monkeypox causes systemic illness and rash, genital, anal, and/or lesions without systemic illness .
• Cowpox affects cattle and results in haemorrhagic ulcers.
• Vaccinia, also found in cattle, is used for smallpox vaccination, causing vesicles and pustules.
• Molluscipoxvirus is transmitted through direct contact or fomites, and it causes Small warty umblicated papules on trunk, buttocks, arms and face.
• Parapoxvirus orf is transmitted through sheep and results in Zoonosis as well as pustular dermatitis, large and granulomatous.

Parvoviridae (Parvovirus)

• Parvoviridae are the smallest DNA viruses.
• They have a single-stranded DNA and the smallest genome (20 nm).
• Erythrovirus (Parvovirus B19) replication occurs only in human erythrocyte precursors.
• Parvovirus B19 is the only known human pathogenic parvovirus.
• Parvovirus B19 is transmitted by respiratory aerosol.
• Parvovirus B19 causes erythema infectiosum (fifth disease, or slapped cheek syndrome).
• Aplastic crisis can occur in chronic haemolytic patients (sickle cell disease or thalasemia).
• Parvovirus B19 can cause persistent infection in immunocompromised hosts.
• Vertical transmission of Parvovirus B19 in pregnancy can lead to severe anaemia.
• Vertical transmission of Parvovirus B19 in pregnancy can lead to hydrops fetalis and congestive heart failure.
• Rare transmissions of Parvovirus B19 through transfusion can trigger aplastic anaemia.

Hepadnaviridae (Hepadnavirus)

• Hepatitis B Virus (HBV) is transmitted via parenteral (injection), sexual contact, and vertical transmission.
• HBV causes acute/chronic infections of hepatitis, cirrhosis, and liver cancer.
• Hepatitis B Vaccine is available in 3 doses for newborns.

Herpesviridae (Herpesviruses)

• There are only 8 herpesviruses known to infect humans.
• All herpesviruses result in latent infections.
• Human herpes viruses includes human herpes virus 1, human herpes virus 2, Varicella zoster virus, Cytomegalovirus, Epstein Barr virus, Herpesviruses 6, Herpesviruses 7, Herpesviruses 8.
• HHV-1 can be transmitted through direct contact or sexual contact and can result in Gingivostomatitis, herpertic whitlow, dendritic ulcer (keratitis), encephalitis
• During Primary infection mucoepithelial cells, Latent site-nerve ganglia is triggered during immune state.
• HHV-2 can be transmitted through sexual or congenital contract with congenital and can result in Genital herpes, Severe neonatal infections, meningitis.
• During Primary infection mucoepithelial cells, Latent site-nerve ganglia is triggered.
• Varicella-zoster virus (HHV-3) is transmitted through aerosol, close contact and congenital contact and can result in Varicella (chickenpox) as a primary infection and Zoster (shingles) : reactivation.
• Cytomegalovirus (HHV-5) is transmitted Direct Sexual Congenital Blood transfusion and transplantation and Mononucleosis

Papovaviridae (Papovavirus)

• Human papillomavirus (HPV) is closely related to genital neoplasia and has >100 types.
• HPV is a dsDNA, naked virus with an icosahedral capsid.
• 30-40 HPV types infect the anogenital region (anus + genital).
• HPV 16 and 18 account for the majority of cervical cancers.
• HPV 6 and 11 are most often associated with external anogenital warts.
• Close contact and sexual contact results in Warts where there is skin on the skin.
• Carcinoma of the cervix, anus, oropharyngeal, subset head and neck squamous cell - ca : HPV 16 and 18
• (At risk: Immunocompromised, MSM) homosexual
• Laryngeal papillomas in children: HPV 6 and 11
• HPV vaccine : Gardasil 9 is available.
• BK virus and JC virus are polyomaviruses.
• Respiratory and Oral can lead to Progressive multifocal leukoencephalopathy (PML) Demyelinating disease in immunocompromised patients.

Adenoviridae (Adenovirus)

• Adenoviridae cause multi-systemic diseases, commonly in paed.
• Adenoviridae diseases present as runny nose, coughing, conjunctivitis, haemorrhagic cystitis or gastroenteritis.
• Primarily affect respiratory systems.

RNA Virus Classification

Caliciviridae (Calcivirus)

• Calciviridae are small, naked ssRNA icosahedral viruses, 27-38 nm.
• There are 2 genera- Norovirus and Sapovirus
• Calcivirus is an extremely hardy virus and resistant to being infected after being exposed to acid, ether and heat (60C for 30 minutes)
• Calcivirus transmits through contaminated food and water (fecal-oral spread) and results in Gastroenteritis

Hepeviridae (Hepevirus)

• Hepeviriae have a small naked icosahedral surface, 27-34 nm with spikes the surface.
• Hepeviride transmits faecal orally and result in endemic hepatitis in countries with poor sanitation

Picornaviridae (Picornavirus) – 7.

• 1 Naked, ssRNA, icosahedral capsid
• 2 Usually transmitted via fecal-oral
• 3 Mostly asymptomatic
• 4 Severe complications (rare) may occur in

Reoviridae (Reoviruses)

• Reoviridae include Respiratory Enteric Orphan and Four of nine genera
• Reoviridae result in a icosahedral, double-shell capsid
• Reoviridae have a double stranded RNA genome (dsRNA)
• Vector borne
• Rotavirus A-C groups - cause human disease
• Rotavirus is through Fecal Oral transmission with the vaccine available and can result in Acute gastro-enteritis in children (mild to severe. Associated with mortality and on EM: Wheel like appearance. Latin 'rota'

Coronaviridae- coronaviruses

• Coronaviridae are ssRNA, enveloped, helical nucleocapsid
• Coronaviridae is transmitted through droplet aerosol can may also be detected in faeces
• The primary hosts of Coranaviridae is humans
• Transmission through droplet aerosol results in Cold upper respiratory infection

Orthomyxoviridae (Orthomyxovirus)

• Transmits Genetic variation occurs on H and N of influenza A and B
• Envelope glycoproteins include hemagglutinin (H) and neuraminidase (N). e.g: H1N1 Segmented genome

Paramyxoviridae (Paramyxoviruses)

• 2 types of envelope glycoproteins - hemagglutinnin (H) and neuraminidase (N) activities; another assists in membrane fusion-F protein •  3 genera
•  Paramyxovirus (H & N activities)
• - Parainfluenza virus
• -- Mumps virus, vaccine available Morbillivirus (H activity only)
• -Measles virus, vaccine available
• ---Nipah virus Pneumovirus (No H nor N activity)
• -Respiratory syncytial virus (RSV) Common in infant Transmitted by droplets

Togaviridae (Togaviruses) - arthropod borne ar/bo/viruses

•  Majority of arboviruses are in the Alphavirus genera
•  Mosquitoes are the vectors of alpha viruses
•  Rubella:
•  Transmission: respiratory droplet direct contact, placental transfer (congenital infection)
• Chikungunya - Fever (dengue-like), myositis-arthritis, Monkeus
• Rubella-* Rubella; congenital syndrome (severe fetal malformation), man droplets
• Vaccine available

Flaviviridae (Flaviviruses)

•  Most flaviviruses are arboviruses.
•  Russian spring-summer encephalitis virus may also be transmitted thru milk For almost all flaviviruses, birds and animals are the natural hosts
•  Man is only an accidental host For the dengue virus, man is the only host Yellow Fever Monkeys - Jaundice, Haemorrhagic fever Dengue- ManFever, Dengue Haemorrhagic Fever, dengue shock syndrome Japanese encephalitis Birds Encephalitis

Bunyaviridae (Bunyaviruses)

• 4 genera- Bunavirus, Phlebovirus, Nairovirus, Hantavirus
• Spherical, enveloped, ssRNAvirus All are arboviruses except hantavirus.
• Present in Malaysia
• Haemorrhagic fever & renal syndrome (HFRS)
• -Mammals
• Vector-(mosquitoes Encephalitis encephalitis

Rhabdoviridae (Rhabdovirus)

Bullet-shaped, envelope stray Transmitted via saliva of rabid animals by deep penetrating bite wounds, abrasions or scratches on skin, mucous membranes exposed to saliva from licks. Inhalation in bat-infested caves, corneal transplant.

Filoviridae (Filovirus)

• Tubular shaped, enveloped viruses with ss, unsegmented, helical RNA genome
• Transmitted via direct contact with blood (parenteral)

Arenavirus

• Rodents (mice) are their hosts
• Man is infected thru dried rodent feces, probably via aerosol