Why Hepatitis B Core Antigen (HbcAg) is not detected in Serum?

During the lab diagnosis of  Hepatitis B, we perform serological tests. In which we can detect Antigens, HBsAg, HBeAg, Anti-HBs, Anti-HBc (Antibody against Hepatitis B core antigen). You might have wondered if there is antibody in the serum against Hepatitis B core antigen, why dont we can detect Hepatitis B core Antigen (HBcAg) from the serum.

 In this blog post i have collected some information so clarify about this issue. 

Hepatitis B c Antigen (HBcAg) is an intracellular antigen synthesized within infected hepatocytes. Hepatitis B core antigen (HBcAg) are expressed by infected hepatocytes.

Hepatitis B Core Antigen production and Assembly source: http://depts.washington.edu

 Most of the HBcAg that is generated is assembled into the viral core (nucleocapsid).

Geological name of Microorganisms and Microbial diseases

The name of the microorganisms and the microbial diseases are some times dervied from the place of first isolation of the organism or occurrence of the disease. Some times these names create confusion because the organism initially isolated from particular location, now may be prevalent all over the world so is the disease.

In this blog post I have compiled the list of some of the viruses, viral disease, bacteria and bacterial diseases etc so that you can see the disease and organism in alternative ways also. I hope you will enjoy this blog post, please do let forget to share with friends and  leave a comment if there is something important you want to share with me.

Laboratory Diagnosis of Influenza Virus

For the laboratory diagnosis of Influenza Virus, specimen should be taken as early as possible during the course of disease preferably within the first 72 hour after the onset of symptoms. Routine Specimens for Influenza Virus diagnosis include
A. Nasal Washings
B. Nasopharyngeal aspirate
C. Nasopharyngeal swab
D. Nasal and Throat swabs
For successful isolation, specimen should be placed on transport medium to stabilize the virus.

Isolation of Influenza Virus
a. Cell Culture
Madin-Darby Kidney Cell Line (MDCK) Supplemented with trypsin supports growth and multiple cycle of influenza A, B and C. Standard virus isolation is done in cell culture tubes seeded with MDCK Cells. The cultures are incubated at 34 degree centigrade either in stationary rack or in a roller machine. Some influenza viruses cause a distinct cytopathic effect in MDCK cells, several days after inoculation. Negative Cultures should be checked by a hemadsorption or hemagglutination test at two to three days interval.

LABORATORY DIAGNOSIS OF HEPATITIS B VIRUS

T.U 2O59,2061,2062

LABORATORY DIAGNOSIS OF HEPATITIS B VIRUS

Hepatitis B Surface Antigen (HBsAg)  is the most important serological marker for identifying infection with Hepatitis B Virus.
HBsAg is present early in acute infection, disappears with resolution of infection and persists in chronic infection.

IgM anti-HBc (IgM class antibody, against Hepatitis B Core Antigen) is essential for the diagnosis of acute infection, but is also seen occasionally in very active chronic hepatitis. Anti-HBc antibodies develop and persist after all HBV infections. The loss of HBsAg and development of anti-HBc signals resolution of acute infection.
Anti-HBs also occurs post vaccination, but anti-HBc will not be present in such cases.

STRUCTURE CLINICAL FEATURE AND LAB DIAGNOSIS OF HERPES SIMPLEX VIRUS

T.U 2058, 2060

STRUCTURE CLINICAL FEATURE AND LAB DIAGNOSIS OF HERPES SIMPLEX VIRUS

These viruses are members of the Alphaherpesvirinae subfamily of human

herpesviruses together with varizella-zoster virus, also called human herpesvirus. HSV is a large virus with a core containing double-stranded DNA within a coat, an icosahedron with 162 capsomeres. The envelope which surrounds the ‘naked’ particle is partly nuclear membrane derived, partly virally coded, with glycoprotein spikes. The diameter of a complete particle is 120–200 nm. The ‘naked’ virion measures about 100 nm.

Expalain the characters and laboratory diagnosis of Hepatitis B virus.

Expalain the characters and laboratory diagnosis of Hepatitis B virus.

Hepatitis B VIrus is a member of the Hepadnaviridae family. It is the only DNA virus among the agents which commonly cause viral hepatitis. The viral particle (called the Dane particle) is 42 nm in diameter. The lipoprotein (HBsAg) which  encoats the virus is seen not only as a viral envelope but also by electron microscopy as free non-infectious tubular and spherical structures. These forms of HBsAg circulate in considerable excess compared with the virion and may play a permissive role in viral persistence. However, HBsAg may be present in blood when replication cannot be documented.

Continuous cell line

Continuous cell line

At any time during the culture of a cell strain, cells in the culture may become transformed, meaning that they are no longer subject to crisis and senescence but can be passaged indefinitely. i e the transformed cells become immortalized. Immortal cell cultures are called cell lines, or sometimes continuous cell lines, to distinguish them from primary cultures and cell strains. Eg HEp-2 cells. Immortalization can occur spontaneously during passage of a cell strain, or it can be induced by treatment with chemical mutagens, infection with tumorigenic viruses, or transfection with oncogenes. In addition, cells cultured from tumor tissue frequently readily establish immortal cell lines in culture. Immortalization is typically accompanied by genetic changes—such cells become aneuploid, containing abnormalities in the number and structure of chromosomes relative to the parent species, and not all cells in a culture of a continuous cell line necessarily display the same karyotype. Like cell strains, cell lines are usually composed of cells that are either fibroblast-like or epithelial-like in morphology.

As with the propagation of cell strains, continued culture of a cell line may result in selection of specific variants that outgrow other cells in the culture over time, and thus with passage the character of a cell line may change substantially, and cell lines of the same origin cultured in different laboratories over a period of years may have significantly different characteristics. It is prudent, therefore, to freeze stocks of cell lines having specific desirable properties so that these cells can be recovered if the properties disappear during culture. Likewise, it makes sense to obtain a cell line showing certain desired characteristics directly from the laboratory that described those characteristics, because cells from alternative sources may differ in character 

DESCRIBE STRUCTURE OF HIV VIRUS: T.U 2058

DESCRIBE STRUCTURE OF HIV VIRUS: T.U 2058

HIV is a complex RNA virus of the genus Lentivirus within the Retroviridae family. The virus is an approximately 100nm icosahedral structure with 72 external spikes that are formed by the two major envelope glycoproteins gp120 and gp41.

Structure of HIV Virus: Cross-Section

The lipid bilayer is also studded with a number of host-cell proteins during the budding process. HIV has a characteristic dense, cone-shaped nucleocapsid composed of the core protein p24. This nucleocapsid harbours two copies of the 9.8 kb single-stranded RNA genome which are associated with the viral enzymes reverse transcriptase (RT), RNase H, integrase and protease. In addition to structural genes HIV has genes whose products contribute to the complex regulation and replication of the virus. Of particular interest is the Nef (negative factor) protein.
Deletions and mutations of this protein have been found in some HIV-infected individuals characterized as long-term non-progressors. Two major types of the AIDS virus, HIV- 1 and HIV-2, have been identified. The major serological differences reside in the surface protein gp120. HIV-1 and HIV-2 are further separated into subtypes or ‘clades’ due to the marked variability in the V3 (variable region) of the gp120 protein. Infectivity is destroyed.

Salk and sabin vaccine (T.U 2063)

Salk and sabin vaccine (T.U 2063)

Two types of vaccine are available against poliomyelitis, inactivated vaccine (IPV, Salk) and live attenuated oral vaccine (OPV, Sabin). Both vaccine formulations contain all three polio types.

Sabin or OPV

OPV is the most widely used vaccine for prevention of poliomyelitis. It is composed of attenuated strains of the three poliovirus types, and is administered orally.

Human Immuno Deficiency Virus (HIV VIRUS)

HIV

Viron: spherical, 80-100 nm diameter, cylindric, core (ribonucleoprotein)

Genome: ss RNA, linear, diploid, 9-10kb, +ve sense.

Proteins: RT, Env gp, protease

Envelope: present, acquired from the host cell membrane when budding out of cell.

·        non- oncogenic, may be cytocidal, provirus remain permanently associated with cells.

Genome

-         contain in the same order the genes: gag, pol and env → 5’- gag- pol- env – 3’

-         LTR of both ends of genome contain promoter and enhancer sequences.

-         Gag → group specific Ag ( associated with virion core)

-         env → type- specific / sub group specific (gp of envelope)

-         pol → RT, IN, PR, endonuclease .

-         at least 6 regulatory genes.
- tat (transactivating)
→ general stimulating effect on synthesis of all viral proteins.
- rev(regulatory effect)
→ for expression of viral structural protein.
- nef (negative factor)
→ downregulates expression of CD4 and MHCI.
- vpr → increase transport of pre- integration complex into nucleus.
- vif → promotes virion infectivity
- vp4 (HIV-1)/ vpx (HIV- 2)→ enhances maturation and release of progeny virus.

-         Gag- pol precursors cleaved by viral protease PR.

-         Env is cleaved by cellular PR.

-         Regions of greatest divergence localized to env gene.

-         SU (gp 120) unit determine L- and M- tropisms and carries the major Ag determinant .

-         HIV gp has 5 variable regions (V1-V5).

-         Sequences of TM, more conserved that SU.

-         Due to error prone nature of RT.

-         Infected hosts contain “swarms” of closely related viral genomes, k/as ‘ quasi species’

Classification

-         based on molecular and antigen difference, 2 types of human AIDS viruses,
HIV-1 and HIV-2 → much less virulent; related more to SIV; largely confined to west Africa.

-         Based on env gene sequences, HIV-1 has 3 distinct group: M (major), N(new), and O (outlier).

-         M group contains 9 subtypes / clades (A-K, omitting E and I).

REPLICATION

-         Replicate via an integrated ds DNA stage.

-         RT( RNA directed DNA polymerase) coded by pol gene has 4 activities ( protease, polymerase, RNase H, and integrase).

-         Following entry, synthesis of DNA complementary to viral RNA occurs using RT; primer is a specific t-RNA eg tRNA ^lys

-         Sequences from both ends of viral RNA become duplicated, forming the LTR located at each end of viral DNA.

-         RNase H activity of RT digests RNA from a DNA- RNA hybrid, resulting ssDNA made ds by pol. Activity of RT.

-         Linear ds DNA able to circularize.

-         Integration of circular DNA into host cell DNA → provirus
→ site of insertion non specific
→ provirus flanked by a 4-6 bp direct repeat of host DNA.
→ integrated state is stable and viral DNA replicates along with cellular DNA.

-         Proviral DNA transcribed by host enzyme, RNA pol II.
→ full length transcripts serve as genomic RNA.
→ some transcripts are spliced and the subgenomic mRNAs, translated to produce viral precursors proteins;viral protease involved.

-         Provirus remains integrated within cellular DNA for life of the cell.

HIV PATHOGENESIS

picorna viridae

PICORNAVIRIDAE
• enterovirus • rhinovirus
- nonenveloped viruses, 27-30 nm, resistant to ether and other lipid solvents.
- 60 subunits, RNA (30%), protein (70%).

-         genome → SS RNA, linear, (+) sense, 7.2-8.4 kb, infectious, genome linked protein (VPg).
→ Replication → cytoplasm

STRUCTURE / COMPOSITION
- capsid shell → 60 subunits, each with 4 proteins (VP1-VP4) arranged with icosahedral symmetry around a genome

-         prominent cleft or canyon around each pentameric vertex.

-         Receptor binding site located near the floor of the canyon.

-         Genome polyadenylated at 3’ end and a small coded protein (VPg) covalently bound to 5’ end.

-         Enteroviruses stable at acid PH (3.0-5.0) for 1-3 hrs , rhinoviruses are acid – labile.

-         Inactivated by heat (55⁰C for 30 min); MgCl₂ protects virus against heat inactivation.

-         Formaldehyde and oxidizing disinfectants destroy the virus.

Phenolic disinfectants not effective.

POLIOMYELITIS

POLIOMYELITIS
- destruction of motor neurons in spinal cord → flaccid paralysis

-         very restricted host range → natural infection occurs only in humans.

-         Grows readily in tissue cultures of primate origin.

 PATHOGENESIS

-         transmitted by faeco- oral route.

-         Virus multiplies initially in epithelial cells of AC (Oropharynx or intestine) and the lymphatic tissue ( tonsils / payers patches).

-         Regularly present in throat and stools before the onset of illness.

-         Then spreads to the regional lymph nodes and enters blood stream (minor / 2⁰ viraemia) across the BBB.

-         Direct neural transmission may also occur eg after tonsillectomy..

-         In the CNS, Virus multiplies selectively in the neurons destroys the anterior horn cells of spinal cord.

-         Earliest change is degeneration of Nissils bodies.

-         When degeneration becomes irreversible, necrotic cell lyses or is phagocytosed.

-         Viruses don’t multiply in muscle in vivo.

-         Changes that occur in peripheral nerves and voluntary muscles are secondary to destruction of nerve cells.

Clinical findings

-         Incubation period 7-14 days.

-         Inapparent infection: 90-95% cases; only seroconversion.

-         Abortive poliomyelitis: 4-8%; minor illness.
- Fever, malaise, drowsiness, headache, nausea, vomiting, constipation.
- Recovery in few days.

-         Non- paralytic poliomyelitis ( aseptic meningitis) – 1-2%
- above symptoms + stiffness and pain in back and neck; 2-10 days.

-         Paralytic poliomyelitis: 0.1-2%
- flaccid paralysis resulting from lower motor neuron damage.
- Maximal recovery with in 6 months, with residual paralysis lasting much longer.

-         Progressive post – poliomyelitis muscle atrophy: rare
- recrudescence of paralysis and muscle wasting.
- Decades after experience with paralytic poliomyelitis.
- doesn’t appear to be a consequence of persistent infection rather a result of physiologic and aging changes.

Lab diagnosis
specimen: throat swabs, rectal swabs / stool, blood, CSF ( uncommon).

No permanent carriers known.

Specimen should be kept frozen during transmit to lab.
A. Isolation of virus.
- can be isolated from blood and pharyngeal aspiration during 10 viraemia,(3-5 days after infection). From feces → upto 5 weeks.

-         After processing specimen, inoculated into tissue culture.

      •Primary monkey kidney cells, typical CPE in 2-3 days.

       • Identification by neutralization tests with pooled and specific antisera.

-         Virus isolation from feces must be interpreted along with clinical and serological evidence.

B. direct demonstration of virus by electron microscopy
c. serology: less often employed.
- paired serum specimens to show a rise in antibody titer

-         Only 1^st infection produces strictly type- specific responses.

Prophylaxis

Passive immunization is of little value.

Salk killed vaccine
- viral pools of adequate titer filtered and inactivated with formalin (1:4000) 37⁰C / 12-15 days.

-         given by injection, IPV

-         3 doses given 4-6 weeks apart + booster 6 months later.
1^st dose to babies after age of 6 months.

Sabin live vaccine ( OPV).

-         developed by plaque selection in monkey kidney tissue culture on HDCC.

-         Stringent precautions to be taken to ensure freedom from extraneous agents like SV40 and B- virus.

-         Issued either in monovalent or trivalent form; 3 doses at 4-8 weeks interval.

-         Vaccine stabilized by MgCl2; shelf life at 4-80C is 4 monts and at -200C is 2 yrs.

-         Improper storage conditions and cold chain failure partly responsible for apparent failure of OPV.

-         Live vaccines infects, multiplies and disseminated in the community.

-         Produces not only IgM and IgG but also IgA in the intestine, and then becomes resistant to re- infection.

o       Both killed and live vaccines protect the CNS, but gut develops a far increased degree of resistance after administration of live – virus vaccine.

o       OPV not safe in immunodeficient or immuno- suppressed subjects.

o       Interference → if alimentary tract of a child infected with another enterovirus at the time vaccine is given, establishment of polio infection and immunity may be blocked.

o       Frequent diarrhoeal diseases prevent colonization by vaccine virus.

o       Breast feeding immediately before or after vaccine may neutralize the vaccine virus.

o       IG provides protection for a few weeks against paralytic disease, but doesn’t prevent subclinical infection.

o       Effective only if given shortly before infection; no value after clinical symptoms develop.

Measles Virus: Pathogenesis, Clinical Findings and Lab Diagnosis

MEASLES

-         most common cause of child hood fevers.

-         Spikes carry HA but not an NA function; only one serotype.

-         Disease characterized by fever, respiratory symptoms, and a maculopapular rash.

PATHOGENESIS / PATHOLOGY
- human are the only natural hosts.

-         virus gains access via the respiratory tract, infection then spreads to the regional lymphoid tissues.

-         1⁰ viraemia disseminates the virus ( replicates in the RE- system).

-         2⁰ viremia seeds the epithelial surfaces ( skin, respiratory tract, conjunctiva) where focal replication occurs.

-         Multinucleated giant cells with intranuclear inclusions seen in lymphoid tissues through out the body ( lymph nodes, tonsils, appendix).

-         Incubation period is typically 8-12 days ( may be upto 3 weeks in adults)

-         During prodrome (2-4 days) and the first 2-5 days of rash, virus is present in tears, nasal and throat secretions, urine and blood.

-         Characteristic maculopapular rash appears about day 14; rash develops as a result of interaction of immune T cells with virus infected cells in the small blood vessels; in patients with defective CMI no rash develops.

-         Involvement of CNS is common
 • symptomatic encephalitis in about 1:1000 cases.
 •  progressive measles inclusion body encephalitis in patients with defective CMI, actively replicating virus present in the brain in this usually fatal form.
 • subacute sclerosing panencephalits  ( SSPE) develops years, after initial infection.

CLINICAL FINDINGS
- infection in non- immune hosts almost always symptomatic

-         after an incubation of 8-12 days, measles is typically a 7-11 day illness (2-4 days prodrome) followed by eruptive phase of 5-8 days)

-         prodromal phase characterized by fever, sneezing, coughing, running nose, redness of the eyes, kopliks spots and lymphopenia .

-         koplik’s spot ( pathognomonic for measles) are small, bluish- white ulcerations on buccal mucosa opposite the lower molars; these spots contain giant cells and viral Ag and appear about 2 days before the rash.

-         Rash starts on the head, and spreads progressively to the chest, trunk, drown the limbs, appears as light, pink, discrete maculopapules that coalesce to form blotches, becoming brownish in 5-10 days; fading rash resolves with desquamation over the next 10-14 days.

-         Most common complication is otitis media( 5-9% of cases).

-         Pneumonia is the most common life threatening complication caused by 2⁰- bacterial infections; pulmonary complications account for > 90% of measles – related deaths.

-         Giant cell pneumonia a serious complication in people with CMI deficiency.

-         Complication involving CNS in about 1: 1000 cases.

-         Post infectious encephalomyelitis ( acute disseminated encephalomyelitis) is an autoimmune disease associated with immune response to myelin basic protein.

-         Mortality in measles associated encephalitis is about 10-20% ; majority of survivors have neurologic sequelae.

-         SSPE: - incidence of about 1: 300,000 cases.
- disease begins insidiously 5-15 yrs after a case of measles .
- progressive mental deterioration, involuntary movements, muscular rigidity and coma; fatal with in 1-3 years of onset.
- with in the infected cells is a defective form of measles virus, because it is unable to induce the production of a functional M- protein, is not released as complete virus from the cells.
- oligoclonal antibody to viral proteins appear in the CSF.

-         Virus has been linked with multiple sclerosis, pagets disease of bone and Crohns disease.

-         Induces labour in some- pregnant women, resulting in spontaneous abortion or premature delivery.

-         There occurs a suppression of delayed hypersensitivity after measles infection.

IMMUNITY

-         only one antigenic type; infection confers life long immunity

-         presence of humoral antibody indicates immunity; CMI important in recovery and protection .

-         immune response involved in disease pathogenesis.

-         Local inflammation causes the prodromal symptoms.

-         Specific CMI plays a role in development of rash.

-         Infection causes immune suppression → cause serious 2⁰- infection.

LAB DIAGNOSIS
typical cases reliably diagnosed on clinical grounds; lab diagnosis necessary in modified or atypical cases.

Ag detection
Ag detected directly on exfoliated respiratory cells by IFT using Ab to the viral nucleoprotein.

Isolation and identification of virus

-         nasopharyngeal and conjunctival swabs, blood samples, resp. secretions and urine collected during the febrile period.

-         Monkey or human kidney cells or a lymphoblastoid cell line (B95-a) are optimal; virus grows slowly and typical CPE ( multinucleated giant cells containing both intranuclear and intracytoplasmic inclusion bodies) take 7-10 days to develop. → Warthin- Finkeldey cells.

-         Shell vial culture tests can be done in 2-3 days using fluorescent Ab- staining.

Serology

-         4 fold rise in Ab- titer between acute and convalescent sera or demonstration of specific IgM in single serum specimen drawn between 1 and 2 weeks after onset of rash.

-         ELISA, HI and Nt tests used; ELISA is most practical.

-         High titer Ab in CSF is diagnostic of SSPE

Epidemiology

-         virus is highly contagious; there is a single serotype; inapparent infections are rare; human is only natural host, no animal reservoir.

-         Transmission via the respiratory route; haematogenous transplacental transmission can occur; associated conjunctivitis may also be a source.

-         Patients infectious from 3 days before onset of symptoms until the rash desquamates; infectivity max. at prodrome and diminishes rapidly with onset of rash.

-         Epidemic occur every 2-3 yrs; populations state of immunity is a determining factor, severity of epidemic is a function of the number of susceptible individuals; can cause epidemic in an isolated community where it has not been endemic, in such case mortality rate can be as high as 25%.

-         Rarely causes death in healthy people, but in some malnourished children, it is a leading cause of infant mortality.

Treatment / prevention/ control

-         Vit A treatment in developing countries decreased mortality / morbidity.

-         Virus susceptible in vitro to inhibition by ribavirin.

-         A safe and highly effective live attenuated vaccine is available in either monovalent form or in combination (MR / MMR); given at 12-18 months of age.

-         Due to failure in vaccinating children and infrequent cases of vaccine failure, measles has not been eliminated.

-         Mild clinical reactions (fever or mild rash) will occur in 2-5%  vaccinees

-         Ab- titer lower than after natural infection; but immunity probably life long.

-         Contraindications include pregnancy, allergy to eggs or neomycin, immune comprise and recent administration of Ig.

-         Strain used is Edmonston B or Schwanz, seroconversion rate is >90%.

-         Recommended age for vaccination in developing countries is 9 months; a single subcutaneous injection of vaccine provides protection beginning in about 12 days and lasting for over 20 yrs.

Passive immunization → normal human gamma- globulin with in 6 days of exposure can prevent or modify the disease; valuable in children with immunodeficiency, pregnant women and others at special risk.

Mumps Virus: Introduction, Pathogenesis, Clinical Findings and Lab Diagnosis

-         non suppurative enlargement of one or both salivary glands.

-         Causes a mild childhood disease; in adults complications including meningitis and orchitis are common.

-         >1/3^rd of all mumps infection are asymptomatic.

-         A berring- bone or zipper- like RNP is frequently seen to leak from the virions in preparation examined by electron microscope (common to all paramyxoviruses).

PATHOGENESIS

-         human are the only natural hosts.

-         1⁰- replication occurs in nasal or upper respiratory tract epithelial cells; viremia disseminates virus to salivary glands (involvement of parotid glands not obligatory).

-         Incubation period ranges from 2 weeks- 4 weeks (typically 16-18 days); virus shed in saliva from about 2 days before to 9 days after onset of swelling.

-         Mumps is a systemic viral disease.

-         Frequently infects the kidneys; viruria persists for upto 14 days after onset of symptoms.

-         CNS is also commonly infected.

CLINICAL FINDINGS

-         mumps is an iceberg disease, which although common as childhood infection is often subclinical( at least one- third of all infection).

-         After an incubation period of 14-18 days; prodromal period of ‘ flu-like’ illness ( fever, malaise, anorexia) is seen which is followed by developing pain in parotids, which then swell rapidly ( due to blockage of efferent duct), sucking of a lemon infront of a sufferer is a refined form of torture! Paratitis resolves in 1 week.

-         CNS involvement is common ( about 50 % of infection), majority are clinically inapparent ; meningitis in 15% of cases and encephalitis in 0.3%.

-         20-50% of men develop architis ( often unilateral); complication is painful and atrophy of testis may occur, but only rarely does sterility result.

-         Oophoritis in about 5% girls, develops after parotitis resolves.

IMMUNITY
- immunity is permanent after a single infection; even subclinical infection generate life long immunity.

-         there is only one antigenic type and it doesn’t exhibit significant Ag- variation.

-         Ab to HN gp (V-Ag), the F-gp and internal nucleocapsid protein (S-Ag) develop in serum following natural infection; CMI response also develops.

-         Passive immunity from mother confers immunity in infants for 6 months.

-         Ab to S-Ag appear earlier (3-7 days after onset of symptoms) but disappear within 6 months; Ab to V-Ag develop after 4 weeks of onset, but persists for years.

LAB DIAGNOSIS

Lab studies not required to establish diagnosis of typical cases, however may sometimes be confused with enlargement of parotids due to suppuration, drug sensitivity, tumors etc.

Isolation and identification of virus

-         saliva, CSF, urine collected with in few days after onset of illness

-         monkey kidney cells preferred for viral isolation; samples should be inoculated shortly after collection.

-         For rapid diagnosis, IFT to detect viral Ag in 2-3 day cell culture.

-         Virus produces little CPE (cell rounding, giant cell formation)

-         Haemadsorption test to demonstrate presence of haemadsorbing agent.

Serology
Ab- rise detected using paired sera; ELISA or HI test commonly used.

-         Mumps IgM present, early in illness and lasts for 60 days; the heterotypic Ab induced by parainfluenza virus infection don’t cross- react in mumps IgM, ELISA.

-         CFT using S- and V- Ag is also performed.

Epidemiology

-         endemic worldwide; disease incidence highest in children aged 5-9 yrs.

-         Humans are the only natural hosts; transmission by direct contact, air- borne droplets or contaminated fomites.

-         Subclinical cases can transmit the virus.

-         Mortality rate is low (0.01%), mostly due to encephalitis.

Treatment / Prevention / control:

-         no specific therapy

-         immunization with attenuated live mumps vaccine ( made in chick embryo culture) produces a subclinical , non communicable infection; it is available in monovalent form ( mumps only) or in combination with measles and rubella (MMR vaccine) and given as single subcutaneous injection ; provides protection for at least 10 yrs.

-         Vaccine contains the Jeryl Lynn or Urabe strains.

-         Contraindications are pregnancy, immunodeficiency and hypersensitivity to neomycin and egg protein.

Passive immunization not very reliable.

Influenza Virus, Structure, Replication and Pathogenesis

ORTHOMYXOVIRUSES ( INFLUENZA VIRUSES)

-         affinity of the viruses to mucins ( myxa: mucus)

-         4 genera: influenza A, B, C viruses and thogotoviruses

-         Mutability and high frequency of genetic reassortment.
 resultant antigenic changes in viral surface gp.

-         Influenza type A antigenically highly variable and responsible for most cases of epidemic influenza.

Structure / composition

-         virion spherical, pleomorphic (80-120 nm diameter), helical nucleocapsid (9m) SS RNA, (-) sense (13.6 kb genome size) of A and B viruses with and separate segments; infection C → 7 segments lacking neuraminidase gene.

-         Segment
1→ PB₂                   4→HA             7→M₁ and M₂

      2→PB₁                        5→NP             8→NS₁ and NS₂

      3→PA                   6→NA

Schematic representation of Influenza Virus Structure

→ 9 structural proteins; one non- structural

→ NP+ viral RNA → RNP (ribonucleoprotein)
→ PB1, PB2 and PA bound to RNP and responsible for transcription and replication.
→ M1 (matrix) protein forms a shell underneath the envelope.
→ HA and NA (surface gp) determine Ag- variation and host immunity.
→ M2 protein ( ion channel) allows PH changes in the endosome.

Virology Note: Rabies Virus: Structure, Pathogenesis, and Clinical Findings

RHABDOVIRIDAE

-         enveloped, ss RNA viruses with bullet- shaped or rod- shaped morphology

-         2 genera: lyssa virus → rabies virus and vesiculovirus → vesicular stomatitis virus

RABIES VIRUS

A.     STRUCTURE / COMPOSITION

Structure of Rabies Virus

- rod or bullet- shaped (75 x 180 nm) ; one end conical, other planar ( concave).
- Membranous envelope with protruding spikes or peplomers (10 nm) which are composed of trimers of viral gp (G) spikes don’t cover the planar end.
- Beneath the envelope is the membrane or matrix (M) protein layer
- membrane may project outwards from planar end of some virion forming a bleb.
- The core of the virion consists of helical RNP ( group specific antigen).
- Genome is unsegmented, linear, ss(-)sense RNA ( 12kb, MW 4.6 X 10⁶).
- virion contain an RNA dependent RNA polymerase.

Herpes Simplex Virus, Structure,Pathogenesis, Clinical Feature and Lab Diagnosis

Herpes virus

-         Establish lifelong persistent infections / undergo periodic reactivation

-         Reactivated infection different from disease caused by primary infection.

Structure

Virion: spherical, 150-200 nm diameter ( icosahedral), 162 capsomers

Structure of Herpes Simplex Virus (HSV-1)

Envelope: derived from nuclear membrane of infected cell

-         contains viral glycoprotein spikes (8nm long)

Tegument: amorphous, asymmetric structure between capsid and envelope.

Genome: ds DNA, linear, 124-235 kbp, reiterated sequences

Proteins: 35 proteins involved in structure of virion.

-         Genome encodes atleast 100 different proteins.

Replication: nucleus, bud from nuclear membrane.

HERPES- SIMPLEX VIRUSES

-         grow rapidly and are highly cytolytic

-         latent infection in nerve cells
HSV Type I: oropharyngeal lesions / recurrent attacks of fever blisters
                      spread by contact ( infected saliva)
HSV Type II: infects genital mucosa
                       transmitted sexually, vertically

-         growth cycle – 8- 16 hours

-         genome: 150kbp; can encode atleast 70 polypeptides

-         Atleast 11 glycoproteins known.

·         gD: most potent inducer of neutralizing antibody

·        gC: c3b binding protein

·        gE: Fc receptor (IgG)

·        gG: type specific and allow for antigenic discrimination.

·        gH: involved in release of virions.