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Period of
Communicability
There is no evidence of transmission during the incubation period or
convalescence periods. Communicability increases with the severity of
disease and degree of direct exposure. The virus is known to survive in cold
temperatures and in contaminated manure of birds for upto three months. In
water it may survive upto 4 days at 22 degrees C and more than 30 days at
zero degrees C
Portal of entry
Faeco-oral route (amongst human or birds)
Upper respiratory tract among humans
Portal of exit
• Faeces, saliva and nasal secretions of infected birds
• Main upper respiratory tract among humans
Source of infection
• Faeces among birds
• Respiratory discharge among humans
Susceptibility and resistance
• All age and sex groups are susceptible. Most of the cases have occurred
among the poultry bird handlers, which could be explained by length and
degree to the source of infection. Growing concern has been raised in the
scientific community since the onset of outbreak is that there may be a
possibility of reassortment of the H5N1 strain with an existing human
influenza strain among such persons who get exposed to the H5N1 strain while
concurrently suffering from a exposure/episode of human influenza. In such
cases a combination (reassortment) of the two strains may lead to a
new/mutated version of the influenza virus for which currently no medication
and vaccine have been developed and which may carry high transmission
properties and may lead to higher case fatality rates than the H5N1 form.
Initial analysis of viruses isolated from the recently fatal cases in
Vietnam indicates that the viruses are invariably resistant to the
anti-retroviral drugs like M2 inhibitors (rimantidine and amantadine).
Studies to confirm the effectiveness of neuraminidase inhibitors against the
current H5N1 strains are currently underway.
Clinical picture
• Initially flu-like symptoms
• Rapid onset of high grade fever (> 38oC) followed by muscle aches,
headache, sore throat.
• In some cases there may be unilateral or bilateral pneumonia, progressing
to acute respiratory distress requiring assisted breathing on respirator.
Case Fatality Rate (CFR)
• In the current outbreak, the case fatality rate is ranging from 70 - 75 %
among the reported human cases of Vietnam and Thailand
Diagnosis Hemagglutinin inhibition (HAI), ELISA, IFA with HF5 monoclonal
antibodies and RT-PCR have been developed. Virus isolation is the key factor
in identifying the sub-type of the influenza virus
Specimens for laboratory tests
• Throat and/or nasopharyngeal swab
• Nasopharyngeal aspirate
Blood for complete examination and serology
• Blood for molecular biological studies
Collection and transportation of clinical specimens
Procedure for specimen collection among humans
Nasopharyngeal swab
• Insert a sterile swab beneath the inferior turbinate of either nostrils
and leave in place for a few seconds.
• Slowly withdraw with a vigorous rotating motion against the mucosal
surface of the nostril.
• Repeat the same procedure in the other nostril using a new sterile swab.
• Collect the tip of each swab in a vial containing 2-3 ml of viral
transport media (VTM) with the applicator stick broken off.
Throat swabs
• Take a swab after vigorous rubbing from the posterior pharynx.
• Collect the swab into vial with the applicator stick broken off containing
VTM in it.
Nasopharyngeal aspirates
• Nasopharyngeal secretions are aspirated through a catheter connected to a
mucous trap and fitted to a vacuum source.
• The catheter is connected into a nostril parallel to the palate, vacuum is
applied and the catheter is slowly withdrawn with a rotation motion.
• Mucous from the other nostril is collected with the same catheter in
similar manner.
• After collecting mucous from both the nostrils, the catheter is flushed
with 3 ml of VTM.
Sera collection
Collect 3-5 ml of human blood soon after the onset of clinical symptoms. Two
samples need to be taken from each patient, one sample during the first week
of illness and the second 2-4 weeks later.
Postmortem specimens
• Collect tissue and heart blood in fatal cases.
• Divide lungs tissue into two, place half portion in 10% formalin or
formal-saline and the remaining half as fresh.
Procedure for specimen collection among poultry birds
In liaison with designated laboratories, full blood and post mortem
specimens (intestinal contents, anal and oro-nasal swabs, trachea, lung,
intestine, spleen, kidney, brain, liver and heart) may be collected for
identification of virus through similar diagnostic techniques as for humans.
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