Virology

This page is exclusively on the properties of selected viruses that can cause human diseases. Information has been condensed and kept to minimal so that learning becomes easy. A list of viruses is displayed below, click on it and view the properties that appear underneath.

Properties of medically important viruses

Please select individual viruses from the list above to view their properties and the diseases produced.

Properties	Description
Classification	Family: Herpesviridae Sub-family: Alphaherpesvirinae Types: Herpes simplex-1 (HSV-1), Herpes simplex-2 (HSV-2)
Nomenclature	Herpes derived from the Greek word herpein, which means to creep
Morphology	Spherical enveloped viruses measuring 150-200 nm Membrane is derived from host’s nuclear membrane Nucleocapsid is icosahedral in symmetry
Nucleic acid	Double stranded linear DNA; multiplication in host nucleus; replication cycle is approximately 8-16 hours
Antigens	HSV-1 and HSV-2 share many antigenic determinants; glycoprotein G (gG-1) in HSV-1 and gG-2 in HSV-2 are immunodominant.
Types	HSV-1 and HSV-2; have 50% genetic homology
Diseases produced	Grow rapidly and are cytolytic HSV-1 is spread by contact with oral secretions; HSV-2 by genital secretions Virus transmitted by direct contact through skin & mucus membrane Primary HSV infections are usually mild or asymptomatic Incubation period short; 3-5 days Oropharyngeal disease (involve buccal and gingival mucosa; vesicular and ulcerative lesions, gingivostomatitis, pharyngitis and tonsillitis) Keratoconjunctivitis (dendritic keratitis or corneal ulcers, may lead to blindness) Genital disease is acquired as a STD; mainly caused by HSV-2; vesiculoulcerative lesions of the penis, or of the cervix, vulva, vagina and perineum Skin infections (herpetic whitlow, herpes gladiatorum, Eczema herpeticum) Encephalitis is a complication Establishes latent infection; HSV-1 in trigeminal ganglia, HSV-2 in lumbosacral ganglia Recurrent disease (fever blisters/ cold sores/ herpes labialis) commonly at the border of lip
Diagnostic tests	specimen collected from the vesicles/ulcers, throat washings, blood, CSF and corneal scraping Smear stained with Giemsa’s stain, Tzank smear-multinucleated giant cells; Cowdry Type A inclusions; immunofluorescenceor immunoperoxidase Culture on monolayer cells; detected by cyopathic changes, immunofluorescence or nuetalization test Detection of viral DNA by PCR Serodiagnosis by antibody detection; cross-reaction between HSV-1 and HV-2 is common
Antiviral drugs	Acyclovir, valacyclovir, famciclovir and vidarabine useful; intravenous foscarnet or cidofovir for acyclovir-resistant HSV strains.
Prophylaxis	No commercial vaccines yet

Properties	Description
Classification	Family: Poxviridae Sub-family: Chordopoxvirinae Genera: Orthopoxvirus Variola Variola major Variola minor Vaccinia Monkeypox Cowpox Parapoxvirus Orf Pseudocowpox Bovine papular stomatitis Molluscipoxvirus Molluscum contagiosum Yatapoxvirus Tanapox Yabapox
Nomenclature	Variola derived from Latin word varius (meaning "spotted") or varus (meaning "pimple"). Term Smallpox used to differentiate from the "great pox" (syphilis)
Morphology	large, oval or brick- shaped, Measure 400 x 230 nm, outer lipoprotein layer or envelope, contains hemagglutinin proteins, external surface of viral particles contain ridges, contains core and two lateral bodies.
Nucleic acid	Linear, double-stranded DNA genome; replication occurs in host cytoplasm
Antigens	All vertebrate poxvirus have a common nucleoprotein antigen in the inner core. There is immunological cross reaction between members of a genus but little across the genera.
Diseases produced	V. major produced serious form of smallpox with 30-35% mortality; V. minor produced milder form- alastrim, (cottonpox, milkpox, whitepox, or Cuban itch) with fatality of 1%. Clinical types of smallpox: ordinary, modified, malignant, and hemorrhagic. Monkeypox, a zoonotic disease that resembles smallpox; pronounced lymphadenopathy; fatality up to 11%. Cowpox transmitted from infected cow; lesions restricted to hand; fever, regional lymphadenitis; hemorrhagic skin lesion. Orf, also known as contagious pustular dermatitis or sore mouth; transmitted from animals; generally occurs as a single lesion on a finger, hand or forearm; lesions are large nodules, painful with inflamed skin Molluscum contagiosum is benign epidermal tumor; seen only in humans; transmitted by direct contact including sexual; incubation period is upto 6 months; small, pink, wart-like tumors on face, arms, back, buttocks or genitilia
Diagnostic tests	Sample collected: vesiclular fluid, scraping from base of vesicles demonstration of viral antigen by immunofluorescence; includion bodies (Guarnieri bodies, molluscum bodies) culture in embryonated hen's egg, pocks formed, grown on tissue culture; Molluscum contagiosum has not be grown until now detection of viral nucleic acid by molecular methods.
Antiviral drugs	For smallpox: Methisazone, Cidofovir, Ribavirin, ST-246, STI-571
Prophylaxis	For smallpox: Vaccinia virus - a live vaccine; intradermal using forked needle; Complications include generalized vaccinia, progressive vaccinia and post-vacinial encephalitis
Miscellany	Small pox declared eradicated by WHO in 1969 Viable cultures still preserved in two labratories (USA, Russia) Vaccinia virus is able to undergo multiplicity reactivation. ACAM2000 and Imvanex are approved vaccine (mainly for troops); Vaccinia is used as a vector for recombinant vaccines.

Properties	Description
Classification	Family Adenoviridae; divided into seven groups (A–G)
Nomenclature	Named so because it was isolated from explants of human adenoid tissue in 1953
Morphology	Non-enveloped virus Capsid icosahedral symmetry Vertices posses projecting fibre Has hemagglutinating properties
Nucleic acid	Linear, double-stranded DNA; replication in the host nucleus
Antigens	Hexons & penton base give group specific antigen, penton fibers give type specific antigen
Serotypes	57 human serotypes exist
Diseases produced	Respiratory diseases: common cold, tonsillitis, bronchiolotis, pneumonia Eye infections: Pharyngoconjunctival fever and Epidemic keratoconjunctivitis Gastrointestinal infections: infantile gastroenteritis Hemorrhagic cystis; Hepatitis & pneumonia in the immunocompromised
Diagnostic tests	Antibody detection by ELISA, indirect IFA, neutralization, hemagglutination inhibition; fold fold rise in titre significant Infects epithelial cells of the RT, eye, GIT, urinary bladder & liver Can be grown on Primary human embryonic kidney cells, or human epithelial cell lines such as HEp-2, HeLa CPE includes rounding, enlargement, and aggregation of affected cells into grape-like clusters Increased glycolysis in cells results in acidic culture medium Growth can be accelerated by shell vial technique Molecular techniques can rapidly detect viral DNA in clinical specimens
Antiviral drugs	No antiviral drugs
Prophylaxis	Personal hygiene, handwash, chlorination of water
Miscellany	Recombinant Adenovirus used in gene therapy, recombinant vaccine, cancer treatment

Properties	Description
Classification	Family: Parvoviridae, Subfamily: Parvovirinae, Genera: Parvovirus , Erythrovirus (B19) and Dependovirus
Nomenclature	B19 virus was discovered in a blood sample labelled B19 in a blood bank, which was being screened for Hepatitis B
Morphology	Smallest viruses, measure 18-26 nm, non-enveloped, capsid- icosahedral symmetry
Nucleic acid	Linear single-stranded DNA
Diseases produced	Erythema infectiosum or “fifth disease”, is an erythematous illness of childhood transient aplastic crisis that may complicate chronic hemolytic anemia Chronic parvovirus B19 infection in transplant recipients has been linked to anemia, myocarditis, and pneumonitis Immunocompromised patients develop chronic parvovirus B19 infection resulting in chronic anemia Hydrops fetalis seen in nonimmune woman usually in the first 20 weeks of pregnancy; result in fetal death in 2-6% of cases
Diagnostic tests	IgM and IgG antibodies to B19 can be detected by ELISA or indirect immunofluorescence. Viral nucleic acid can be detected by molecular methods
Antiviral drugs	No antiviral therapy is available
Prophylaxis	No vaccine is available

Properties	Description
Classification	Family Herpesviridae, sub-family Alphaherpesvirinae and genus varicellovirus
Nomenclature	Human Herpes virus -3
Morphology	Spherical, enveloped virus measuring 100-110 nm; capsid icosahedral
Nucleic acid	Double-stranded DNA; virus replicates in host nucleus
Diseases produced	Primary infection: chickenpox Mild in children, severe in neonates, elderly & immunocompromised congenital varicella syndrome (premature neonates); complications varicella pneumonia and encephalitis Secondary bacterial infection, pneumonia or sepsis Reactivation: zoster (shingles) Rashes usually appear in a single dermatome on one side Pain & loss of sensation in the affected dermatome Post-herpetic neuralgia Zoster sine herpete: zoster without rashes Myelitis & encephalitis may also occur Ramsay-Hunt syndrome Keratoconjunctivitis
Diagnostic tests	Specimen collected: Skin scraping from base of vesicle, vesicular fluid, CSF, blood Tzank smear show multinucleated giant cells Antigen detection by direct immunofluorescence Vesicular fluid can be cultured on diploid cell lines Presence of viral DNA in CSF (meningoencephalitis) Rise in antibody titre can be demonstrated by ELISA or indirect IFA
Antiviral drugs	Acyclovir, valacyclovir, penciclovir, and famciclovir; strains resistant to acyclovir have developed
Prophylaxis	Varicella immunoglobulin given to those who are exposed and are likely to develop serious disease Administered intramuscularly within 4 days (but up to 10 days) of exposure Active immunization by live attenuated Oka/Merck strain of virus 0.5 ml is administered intramuscularly Children <13 years: First dose at 12-15 months of age, second at at 4-6 years of age For ≥13 years of age should get 2 doses separated by 28 days 98% effective in preventing chickenpox, efficacy 70% in adults Antibody lasts for at least 20 years

Properties of medically important viruses

Herpes Simplex

Pox viruses

Adenovirus

Parvovirus

Varicella zoster

Epstein Barr virus

Cytomegalovirus

Human papillma virus

Influenza virus

Rabies virus

Hepatitis B virus

Hepatitis A virus

Hepatitis C virus

Properties	Description
Classification	Family: Herpesviridae, Syb-family: Gammaherpesvirinae; Genus: Lymphocryptovirus
Nomenclature	Human Herpesvirus 4. It was discovered by Epstein, Achong and Barr in 1964 by electron microscopy in cells cultured from Burkitt's lymphoma tissue
Morphology	Spherical, measure 120-180 nm, enveloped, capsid-icosahedral
Nucleic acid	ds-DNa
Antigens	EBV-EA (early antigen), EBV-MA (membrane antigen), EBV-VCA (viral capsid antigen), Nuclear antigens EBNA 1-3
Types	Two major types, EBV type 1 and EBV type 2
Diseases produced	Infection is acquired through contact with oral secretions Infects epithelial and B cells; infection of B cells results in latency & immortalization of cell In young healthy individuals: Infectious mononucleosis (glandular fever or “kissing disease”); Incubation period is variable- ranges from 33-49 days, resolves spontaneously Malignancies: Burkitt’s lymphoma, Hodgkin’s lymphoma, Nasopharyngeal carcinoma, Oral hairy leukoplakia, CNS lymphomas
Diagnostic tests	Peripheral blood smear shows atypical lymphocytes Paul-Bunnel is a heterophile tube agglutination test involving sheep RBC. Monospot is a slide agglutination test based on the same principle Specific test includes detection of IgA, IgM or IgG antibodies to EB antigens by ELISA, immunoblot assays, and indirect immunofluorescence Detection of EB nuclear antigen in tissue by immunofluorescence or immunohistochemistry can be done EBV DNA can be detected by molecular methods EBV can be isolated from saliva, peripheral blood, or lymphoid tissue by immortalization of normal human lymphocytes, usually obtained from umbilical cord blood
Antiviral drugs	Generally, antiviral treatment is not given. Acyclovir inhibits viral shedding from the oropharynx.
Prophylaxis	No vaccines exist

Properties	Description
Classification	Family: Herpesviridae, Subfamily: Betaherpesvirinae, Genus: cytomegalovirus
Nomenclature	Human Herpes virus 5; causes enlargement of affected cells
Morphology	Spherical, measure 150-200 nm, enveloped, capsid-icosahedral,
Nucleic acid	Linear and non-segmented DNA
Antigens	Matrix protein pp65 antigen
Diseases produced	Incubation period is 4-8 weeks Inapparent infections are common in the childhood Infectious mononucleosis-like syndrome in 20-50% cases Primary infection is self-limiting but establishes life long latency Transplacental infection of the fetus occurs during pregnancy Congenital infection may result in death of the fetus in utero Cytomegalic inclusion disease of newborns is characterized by involvement of the CNS and the reticuloendothelial system Clinical features include intrauterine growth retardation, jaundice, hepatosplenomegaly, thrombocytopenia, microcephaly, and retinitis Infection in the immunocompromised: interstitial pneumonitis, myocarditis, bone marrow suppression, pneumonia, colitis, hepatitis, pancreatitis, nephritis, retinitis and encephalitis In patients with HIV-AIDS, it causes disseminated disease with accompanying gastroenteritis and chorioretinitis Acute or chronic graft rejection and accelerated atherosclerosis
Diagnostic tests	Atypical lymphocytes absent in peripheral blood smear Serum samples test negative for heterophile antibodies pp65 antigen in serum can be detected by immunofluorescence assay CMV can be isolated from saliva, urine by culture on human fibroblast cells Intracellular ("owl's eye") inclusions surrounded by a clear halo may be demonstrated with Giemsa, Wright, hematoxylin-eosin or Papanicolaou Shell-vial technique enchances culture; results available in 1-2 days In primary infection elevated IgM levels are seen; there is 4-fold increase in IgG levels Viral DNA in saliva, blood & tissue samples can be detected by PCR
Antiviral drugs	Ganciclovir is drug of choice; valganciclovir may be used for non-severe CMV infections. Foscarnet is used to treat ganciclovir-resistant strains. Acyclovir and valacyclovir used in bone marrow and renal transplant patients. Cidofovir is used t treate retinitis.
Prophylaxis	CMV immune globulin is administered to high-risk lung transplant recipients along with ganciclovir. Valganciclovir prophylaxis indicated in CMV-positive renal allograft recipients. No vaccines are currently available.

Properties	Description
Classification	Family: Papovaviridae, Genus: Papillomavirus
Nomenclature	Papilloma-warts
Morphology	non-enveloped virus, measuring 55 nm, capsid is icosahedral symmetry
Nucleic acid	circular double-stranded DNA
Antigens	L1 and L2
Types	More than 200 genotype exist
Diseases produced	Transmission occurs via skin-to-skin contact, including sexual; perinatally at childbirth Cutaneous warts (plantar warts, common warts, flat warts) on the hands and feet Heck’s disease is the focal epithelial hyperplasia of the oral cavity Epidermodysplasia veruciformis is warts on the trunk and upper extremities Conjunctival papillomas and carcinoma Throat and laryngeal cancer Condyloma acuminata (genital warts) Squamous cell carcinoma involving primarily the cervix, vagina, vulva, penis, and anus
Diagnostic tests	Cytology and histology; monolayer cytology or biospsy Pap smear is useful in cervical carcinoma HPV cannot be cultured in tissue culture from clinical specimens Immunologic assays are not adequate HPV DNA can be detected by molecular techniques such as PCR
Antiviral drugs	Most cases of cervical cell changes and warts resolve spontaneously within months or years Treatment options for anogenital warts include ablation, excision, or topical agents such as 0.5% podophyllin or 5.0% imiquimod Early invasive cervical cancers are managed with radical hysterectomy or high-energy radiotherapy Concurrent chemotherapy, surgical procedures, antiviral (cidofovir) and immunomodulatory methods (interferon) also followed
Prophylaxis	Two vaccines are commercially available, which offers protection against some HPV types Gardasil is a recombinant quadrivalent vaccine, whereas Cervarix is bivalent; both offer protection against HPV types 16 and 18 Also protects men against anal cancers, warts and genital warts Given in three doses over a period of 6 months

Properties	Description
Classification	Family: orthomyxoviridae, Genera: Influenza A, B and C
Nomenclature	Word influenza derived from "divine influence"
Morphology	Size: 80-120 nm, generally spherical, enveloped, spiral nucelocapsid
Nucleic acid	Single-stranded negative-sense segmented RNA virus; Genome consists of eight gene segments; Influenza C has 7 segments
Antigens & types	Hemagglutinin (HA) and Neruaminidase (NA) are chief antigens. Matrix, nuclear & ion channels are antigens. Influenza A has 17 HA and 10 NA types Influenza A undergoes antigenic variations due to drift (mutations) and shift (reassortment)
Diseases produced	Typical incubation period for influenza is 1-4 days Infections can be asymptomatic, mild upper RTI or complicated lower RTI Pediatric and elderly populations are considered vulnerable during influenza epidemics Pulmonary complications of influenza virus infection include primary viral pneumonia and secondary bacterial pneumonia Elderly individuals are at higher risk for developing hemorrhagic bronchitis, pneumonia, and death Most cases of necrotizing bronchiolitis is associated with bacterial co-infections
Diagnostic tests	Specimen collected: nasopharyngeal swabs, nasal/throat swabs, blood Cultured on embryonated eggs (amniotic cavity) or tissue culture (Monkey Kidney cells) Antibody detected by HI test, netutralization, CFT or ELISA; rise in titre by at least 4-folds is significant demonstration of viral antigen (immunofluorescence) Viral RNA is detected by RT-PCR
Antiviral drugs	Neruraminidase inhibitors such as Zanamivir, Oseltamivir, Peramivir Matrix protein M2 inhibitors such as amantadine or rimantidine Ribavirin inhibits viral polymerase
Prophylaxis	Zanamivir and Oseltamivir can be used prophylactically Killed, subunit or live-attenuated vaccines available. Vaccine includes 2-3 circulating strains of influenza grown in eggs or tissue culture. Recommended for high risk groups Killed vaccine single intra-muscular; immunity for 6-12 months Live attenuated quadrivalent vaccine: nasal spray; attenuated strain capable of growing only at 33°C
Miscellany	There have been at least six recorded pandemics 1889–1890 Asiatic or Russian Flu 1918-1920 Spanish flu 1957-1958 Asian flu 1968-1969 HongKong flu 1977-1978 Russian flu 2009-2010 2009 Flu Pigs are the "mixing vessels" of influenza viruses since they have both α2,6-linked and α2,3-linked SA receptors Influenza A hemagglutinates guinea pig RBCs, Influenza B agglutinates fowl and guinea pig RBCs, whereas Influenza C agglutinates only fowl RBCs, that too at 4°C Hemagglutination by HA proteins are reversed by a process called elution, which is brought about by NA proteins (receptor destroying enzyme)

Properties	Description
Classification	Family: Rhabdoviridae, Genus: Lyssavirus
Nomenclature	Greek rhabdos meaning “rod” referring to the shape of the viral particles. In Greek mythology, Lyssa was the spirit of mad rage, frenzy, and rabies in animals
Morphology	Bullet-shaped virus measuring 180 x 75 nm Envelope; envelope covered with 10 nm long glycoprotein spikes Ribonucleoprotein is helical
Nucleic acid	Single-stranded negative sense RNA. Virions contain an RNA-dependent RNA polymerase
Antigens	Surface glycoprotein, nucleoprotein and matrix protein
Diseases produced	Incubation period for rabies is typically 1–3 months, but may vary from <1 week to >1 year Rabies is a fatal disease; causes meningoencephalitis, paralysis and death Two clinical types: furious (encephalitic) and dumb (paralytic)
Diagnostic tests	Antemortem: Specimens include saliva, CSF, corneal impressions and skin biopsy (facial or neck’s nape), blood demonstration of antigen by immunofluorescence demonstration of nucleic acid by RT-PCR demonstration of antibodies in serum/CSF demonstration of viral culture Postmortem: Brain samples are collected post-mortem by biopsy from cerebellum or hippocampus Viral antigens can be detected by fluorescent antibody test (FAT) or immunoperoxidase tests Eosinophilic intracytoplasmic inclusion bodies (Negri) can be demonstrated by H&E or Seller’s technique
Antiviral drugs	No specific treatment exists; Few cases of treatment as per Mulwaukee Protocol have been successful. It includes induced coma (Ketamin+Midazolam) & antiviral drugs (Ribavirin+amantadine). Four versions of this protocol exists.
Prophylaxis	Pre-exposure, post-exposure and re-exposure regimens exist Pre-exposure prophylaxis Consists of three doses (IM or ID): 0, 7 and either day 21 or 28 High risk individuals should check antibody levels every 6 months If titre <0.5 IU/ml, single booster dose should be taken Post-exposure prophylaxis Depends on category (I, II and III) of exposure Thorough washing of wounds with water and soap followed by application of antiseptics Consists of active and passive immunization Passive immunization by administration of human (HRIG) or equine (ERIG) immune globulin; half is injected intramuscularly, rest is infiltrated around wound Active immunization by vaccines: Neural tissue based, Egg based or Tissue culture based Several dosing regimens exist: on 0, 3, 7, 14, 28 days (Essen Schedule) is commonly followed Two site intradermal injections on days 0, 3, 7 and 28 days is recommended Re-exposure dosage in those who had taken pre- or post-exposure prophylaxis: two doses; 0 and 3 days