The document discusses several viruses that cause respiratory infections including influenza, respiratory syncytial virus, parainfluenza, adenovirus, rhinovirus, and coronaviruses. It notes that respiratory tract infections are very common worldwide and responsible for many lost work days. Diagnosis methods include enzyme immunoassays, immunofluorescent antibody tests, and PCR tests. Treatment depends on the virus but may include antivirals like acyclovir, oseltamivir, ribavirin, and interferon. Herpes simplex virus, Epstein-Barr virus, human papillomavirus, and others are described in relation to various diseases. Conditions with possible viral etiologies include Bell's p

1. Viruses & antiviral agents
DNA viruses are HSV(type 1 & 2), EBV, HPV( over 60types), adenovirus(over 45types).
RNA viruses are coronavirus(two human strain229E & OC4), rhinovirus(over 100types), influenza
virus(A,B ,C),mumps, measles, Respiratory syncytial virus(type A & B),parainfluenza virus(type1,2,3).
Respiratory tract viral infections
Respiratory tract viral infection are the commonest diseases affecting humans worldwide, account
for 30% deaths in the developing countries. Most preschool children experience 6 to 8 viral
respiratory infections per year; episode in adults are responsible for a significant number of lost
working days.
Respiratory tract is one of the commonest sites for viral infection, partly due to accessibility & large
surface area.
Many virus have characteristic seasonal activity. For example;
1. Parainfluenza types 1& 2 out breaks happen predominantly in autumn,
2. Parainfluenza type 3 in spring;
3. Respiratory syncytial virus(RSV) outbreaks during winter.
Pathogenesis
Respiratory viruses infect cells by binding host cell receptors( intercellular adhesion molecule
receptor(ICAM-1)). Systemic symptoms due to interferon & local symptoms due to bradykinins.
Diagnosis
1. Enzyme immunoassay & immunofluorescent-labelled antibody against viral antigens allow
rapid detection.
2. PCR can detect viral nucleic acid.
3. Some virus are detected by specific antibody test(IgM early, IgG at late).
Viruses causes respiratory illness
Illness Virus
Pharyngitis Parainfluenza virus/adenovirus/influenza A&
B/HSV/coxsackie/enterovirus.
Pneumonia/pneumonitis RSV/parainfluenza virus
type3/rhinovirus/coronavirus
Common cold Rhinovirus /coronavirus/ parainfluenza type 4
Cruop Parainfluenza types 1, 2 & 3/RSV/ influenza virus

2. Bronchiolitis RSV/ parainfluenza type 3/influenza
Flu Influenza A & B
Bronchitis Parainfluenza/RSV
1. Coronavirus ;is the largest human RNA virus. There are two strains (229E & OC4) that infect
nasal mucosa, trachea, alveolar cells. It causes 10% of cases of common cold. Infection
causes nasal discharge, malaise. Cervical lymphadenitis, cough, fever are less common.
2. Adenovirus :double stranded DNA virus originally isolated from human adenoid tissue. Over
45 serotypes are present. Adenovirus causes outbreaks of upper& lower respiratory tract
illness in institutions & communities in winter.
3. Rhinovirus : small non-enveloped RNA virus with over 100 serotypes. Replications is
restricted to cells of the upper respiratory tract at 330C temperature.
4. Influenza virus : is an orthomyxovirus with subtypes A,B & C. Outbreaks often begins
suddenly peaking within 4 weeks. Typical symptoms include fever,chills, headache, myalgia,
anorexia & malaise. Primary viral pneumonia may occur or due to secondary staphylococcus
aureus superinfection. In Suspectible people , infection may cause exacerbation of COPD,
asthma, heart failure.
Annual immunization is recommended each autumn for those considered at great risk of
serious complications including the elderly, DM, chronic liver disease, respiratory & renal
disease, immunosuppression.
Avian H5N1 influenza is particularly virulent & has capacity to infect humans resulting in
significant mortality. It originate from wild & domestic birds.
5. Mumps: highly infectious RNA virus. Fever & malaise occur at the onset & parotid swelling
occur within one to two days. One in five men develops orchitis if mumps is contracted after
pubery.atrophy occur 1/3rd although sterility is uncommon. Others complications are
encephalitis, meningitis wtih residual hearing loss. Serum amylase level are increased if
pancreatitis. Incubation period 2 to 3weeks.
6. Measles : incubation period 14days causes infection of children of 3 to 6yrs.
-Typical symptoms are rhinrrhoea, cough, fever & koplik’s spot
-few days later maculopapular rash appear startingon face, then trunk & limbs.
-bronchitis, pneumonia & diarrhoea.
7. Respiratory cyncytial virus: is a RNA virus with two serotypes A & B. This virus is particularly
contagious & causes winter outbreaks in infant . It causes necrosis of bronchiolar epithelium causing

3. bronchiolitis. Ribavirin or steroids reduces morbidity or mortality. Ribavirin as a prophylaxis is
generally reserved for high-risk infants.
8. Parainfluenza virus nearly of all respiratory tract infections. PIV 1 & 2 cause autumn croup
outbreaks every one to two years. PIV 3 is endemic causing bronchiolitis. Type 4 is less
common & can cause upper& lower respiratory tract infection. Parainfluenza virus causes
exacerbations of COPD, asthma. Nebulised ribavirin has been used in PIV infection in children with
immunodeficiency.
Herpes viruses
Herpes simplex virus
Herpes simplex viruses (HSV) are double stranded DNA viruses. Types1 & 2 both cause primary
infection & reactivation.
After entry into skin, the virus replicates locally forming vesicles of degernating cells & fluid.HSV then
tracks along sensory nerves & remain dormant in sensory ganglia. Reactivation is precipitated by
several factors including trauma, stress, menstruation, fever, extreme intemperature & ultraviolet
light.
HSV-1 is mostly contracted from oral & HSV-2 from genitourinary secretions.
During primary oral disease, an incubation period of between two days & two weeks is followed by
sore throat, pharyngitis & febrile illness. Painful vesicles may develops on the oropharynx, checks,
lips, persisting for several days. Others complications includes encephalitis, meningitis, erythema
multiforme, eczema herpeticum. HSV is implicated in the aetiology of Bell’s palsy.
Recurrent infections
Recurrent labial infection begins with symptoms of itching, burning, tingling & pain lasting between
six hours & two days. Lesion occur on the lips & perioral skin.
Multiple recurrences are usually at the same site, some become secondarily infected with
staphylococcus aureus.
Treatment
1) Although topical preparations are used for labial herpes, systemic treatment is required for
severe or recurrent episodes. Famcyclovir / valacyclovir are generally used in preference to
acyclovir as they have better oral absorption. Although drugs reduce the severity & duration
of symptoms, they do not eradicate the virus. Antivirals should be used immediately
preferably before any vesicles develop.
2) Intermittent therapy where treatment is taken before exposure to the trigger factor(stress,
fever) . Using this approach recurrence can be reduced by 80% using famcyclovir & 50-70%
by acyclovir.
3) Patient who experience more than 6 to 12 episodes per year should be considered for long
term prophylaxis with minimum dose to prevent recurrence.

4. 4) In immunocompromised patients, recurrence may be prolonged & severe. Long-term
therapy may be required & carries the risk of drug resistance.
5) In recurrent herpes simplex famcyclovir or valacyclovir should be taken immediately
symptoms begin.
Epstein-Barr virus
Epstein-Barr virus(EBV) is a DNA virus that infect B lymphocytes & epithelial cells of both oral &
genital tracts. Primary infection is often subclinical resulting in asymptomatic life-long carriage.
Infectious mononucleosis arises in approximately half of young adults who are not infected during
childhood.
Symptoms includes sore throat, fever disproportionate fatique. Generalised lymphadenopathy &
hepatosplenomegaly usually resovled within one or two weeks. The infection appears to initate the
onset of recurrent bacterial tonsillitis in a proportion of the patients. These patients often fail to
resolve with time & some require tonsillectomy. There may be periorbital oedema & maculopapular
rash is typical in those taking ampicillin.
Viruses & malignancy
Several human viruses are associated with malignancy by interfering with cell proliferation &
growth. Insertion of viral DNA into a region which interrupt a tumour suppressor gene can confer
malignant properities to the host cell.
Epstein-Barr virus (DNA virus) causes a number of malignant diseases including nasopharyngeal
carcinoma, Burkitt’s lymphoma & B-cell lymphoma.
Human papilloma virus DNA virus with a predilection for human epithelial cells. Of the 60 types
that exist, Perinatal acquisition of HPV types 6& 11 from an infected maternal genital tract may
result in juvenile-onset recurrent respiratory papillomatosis. Although caesarean section is effective
in reducing transmission of HPV. It is not routinely practised owing to the large number needed to
avoid one case of infection. HPV vaccination are currently being evaluated. Oral papilloma/ multiple
papillomatosis/ largngeal papillomatosis/ laryngeal carcinoma/ inverted papilloma can be occurred.
Antiviral agent
Antiviral agents target specific points of the virus replication cycle. Virus uncoating is inhibited by
amantadine with activity against influenza A, DNA polymerase inhibitor/ virus release.
1. Interferon; are naturally occurring substances with antiviral properities. Virus-infected cells
release soluble factors in response to viral infection. Unpleasant adverse effects such as flu-like
symptoms & haematological complications limit its use. Alpha interferon is used with
success, in chronic hepatitis B & C infection with lamivudine& ribavirin respectively.
2. Acyclovir ; DNA polymerase inhibitor. Acyclovir is used in the treatment of HSV &HZV
infection.

5. 3. Influenza neuraminidase inhibitors; zanamivir is an influenza A & B neuraminidase inhibitor
administered by powder inhalation. Administration is recommended within 48hours of
symptoms. Oseltamivir is similar effective & is safe & well tolerated.
4. Ribavirin : Ribavirin is a synthetic analogue of guanosine. It has good activity against a range
of viruses including RSV,measles, influenza virus, hepatitis A,B,C as well as HIV. It is used in
hepatitis C infection . It also used in RSV infection by aerosol inhalation.
Conditions with a viral aetiology
1)Bell’s palsy
Bell’s palsy is an acute , idiopathic,lower motor neurone unilateral facial paralysis. The incidence is
approximately 20 per 100000 per year & increases with age. Equal sex predominance.
Although cause is not clear, a number of aetiologies are suspected, including viral infection, vascular
ischaemia & autoimmune disease. Viral reactivation theory became popular after detection of the
HSV-1 genome. Accepted treatment is prednisolone 1mg/kg per day.
2)Inverted papilloma
Human papilloma virus type 6 &11 are associated with inverted papilloma.
3)Sensorineural hearing loss
Rubella, mumps, measles, herpes zoster, cytomegalovirus, influenza virus.
4)Viral acute otitis media
Viruses causing upper respiratory tract infection are important in the aetiology of acute otitis media.
Rhinovirus & RSV are most commonly detected. Adenovirus, coronavirus, Parainfluenza virus
infection(PIV) are less commonly detected.

6. 3. Influenza neuraminidase inhibitors; zanamivir is an influenza A & B neuraminidase inhibitor
administered by powder inhalation. Administration is recommended within 48hours of
symptoms. Oseltamivir is similar effective & is safe & well tolerated.
4. Ribavirin : Ribavirin is a synthetic analogue of guanosine. It has good activity against a range
of viruses including RSV,measles, influenza virus, hepatitis A,B,C as well as HIV. It is used in
hepatitis C infection . It also used in RSV infection by aerosol inhalation.
Conditions with a viral aetiology
1)Bell’s palsy
Bell’s palsy is an acute , idiopathic,lower motor neurone unilateral facial paralysis. The incidence is
approximately 20 per 100000 per year & increases with age. Equal sex predominance.
Although cause is not clear, a number of aetiologies are suspected, including viral infection, vascular
ischaemia & autoimmune disease. Viral reactivation theory became popular after detection of the
HSV-1 genome. Accepted treatment is prednisolone 1mg/kg per day.
2)Inverted papilloma
Human papilloma virus type 6 &11 are associated with inverted papilloma.
3)Sensorineural hearing loss
Rubella, mumps, measles, herpes zoster, cytomegalovirus, influenza virus.
4)Viral acute otitis media
Viruses causing upper respiratory tract infection are important in the aetiology of acute otitis media.
Rhinovirus & RSV are most commonly detected. Adenovirus, coronavirus, Parainfluenza virus
infection(PIV) are less commonly detected.