The document discusses emerging viral diseases including Japanese Encephalitis, SARS, and Chikungunya, detailing their origins, clinical features, and epidemiology. Japanese Encephalitis is primarily transmitted by Culex mosquitoes and can cause high mortality rates and neurological sequelae; SARS is a respiratory illness caused by a coronavirus that emerged in 2002 and led to a global outbreak; Chikungunya, transmitted by Aedes mosquitoes, causes severe joint pain and has multiple genotypes. Control measures for these diseases include mosquito management, quarantine practices, and the development of vaccines for some but not all.

1. Emerging Viral Diseases
Japanese Encephalitis, SARS & Chikungunya

2. • Emerging infectious diseases can be defined as those that have
appeared for the first time in a population or which have existed
previously but are rapidly increasing in incidence or geographical
range

3. Japanese Encephalitis
• This virus occurs from East Asia to South Asia, from Korea and
Japan in the north to India and Malaysia in the south
• The disease has been recognized in Japan since 1871 and was
named Japanese ‘B’ Encephalitis to distinguish it from
‘Encephalitis A’
• First isolated in Japan during an epidemic in 1935
• Epidemics show seasonal incidence (summer-autumn) in the
temperate regions

4. Morphology
• enveloped virus about 50 nm in diameter with a
single stranded (ss), plus sense, RNA genome of
~11 kb in length
• The genome is organized into a capsid formed
by multiple copies of capsid C protein; which is
covered by a host derived lipid bilayer
• The genome has one open reading frame (ORF)
encoding for a single polyprotein, which is
cleaved into 3 structural proteins e capsid C,
precursor to membrane (prM), envelope E and 7
non-structural proteins: NS1, NS2A, NS2B, NS3,
NS4A, NS4B, NS5, by viral proteases and host
signalases, post translationally

5. Clinical Features
• Culex tritaeniorhynchus, a rural mosquito that breeds in rice
fields, is the principal vector
• The disease has an abrupt onset with fever, headache and vomiting
• After 1-6 days, signs of encephalitis set in with nuchal rigidity,
convulsions, altered sensorium and coma
• The fever is high and continuous
• There is presence of neutrophil leucocytosis in peripheral blood
and pleocytosis with normal or raised sugar levels and slightly
raised protein levels in the CSF

6. Clinical Features
• The mortality rate in some epidemics has been upto 50%
• Upto 50% survivors may have neurological or psychiatric sequelae
• Infection in pregnant women during first and second trimester has
led to fetal death
• In India, JE was first recognized in 1955 when the virus was
isolated from mosquitoes of the Culex vishnui complex from
Vellore during an outbreak of encephalitis in Tamil Nadu
• The virus was continued to be active in TN and Andhra, causing
illness mainly in children, indicating epidemic nature of the virus

7. Clinical Features
• Most of the cases occur between October and November
• Since 1976, the highest rates of human disease have been reported
from the states of Andhra Pradesh, Assam, Bihar, Haryana, Goa,
Karnataka, Kerala, TN, UP and West Bengal

8. Epidemiology
• Herons act as reservoir hosts and pigs as amplifier hosts
• Human infection is a dead end event and occurs when the infected
mosquitoes reach high density
• Natural infection has been demonstrated in Ardeid birds (herons
and egrets);bird-to-bird transmission also takes place through
Culex tritaeniorhynchus
• The mosquito Culex tritaeniorhynchus has a predilection for cattle
and bites them in preference to humans or pigs, but cattle do not
develop viremia, hence do not spread the virus
• The high cattle-pig ration in India has been suggested to be a
factor limiting human infection

9. Control measures
• Preventive measures include mosquito control and locating piggeries
away from human dwellings
• Vaccine is available
• Vaccine:
A formalin-inactivated mouse brain vaccine using the Nakayama
strain, two doses at two weeks interval followed by a booster dose 6-
12 months later
A live attenuated vaccine has been developed in China from JE strain
SA 14-14-2, passed through weanling mice, two doses, one year apart

10. Severe Acute Respiratory Syndrome (SARS)
• A group of spherical or pleomorphic enveloped RNA viruses,
carrying petal or club shaped peplomers on their surface –
Coronaviruses
• There are two groups – acid-labile viruses (associated with
common-cold like illnesses) & acid-stable viruses (associated with
human and animal gastroenteritis)

11. Morphology
• Coronaviruses (CoVs) are enveloped single-stranded
positive sense RNA viruses that belong to the family
Coronaviridae
• SARS-CoV-2 has surface viral proteins, namely, spike
glycoprotein (S), which mediates interaction with cell
surface receptor ACE2
• The viral membrane glycoprotein (M) and envelope (E)
of SARS-CoV-2 are embedded in host membrane-derived
lipid bilayer encapsulating the helical nucleocapsid
comprising viral RNA

12. Epidemiology
• In November 2002, Guangdong province in South China
experienced an outbreak of an unusual respiratory infection, with
many deaths
• The world outside knew about it only in February 2003, when a
physician from Guangdong visited Hong Kong, fell ill and died
there, after infecting 12 persons who had stayed in the same hotel
• They initiated outbreaks in countries where they went
• By July, when the pandemic was controlled, it had affected over
30 countries with many thousands of cases and over 800 deaths

13. Epidemiology
• The coronavirus responsible for SARS appears to be a new virus
distinct from other coronaviruses which had been classified into
three types : Mammalian viruses in types 1 and 2 and Avian viruses
in type 3
• The new SARS virus is coronavirus type 4
• SARS spread by inhalation of the virus present in droplets or
aerosols of respiratory secretions of patients
• Fecal aerosols also may be infectious
• Incubation period is under 10 days

14. Clinical Features
• The disease starts as a fever with cough or other respiratory
symptoms
• Diarrhoea is sometimes seen
• The chest radiograph shows pneumonic changes
• Death is due to respiratory failure
• Middle East Respiratory Syndrome (MERS), first detected in Saudi
Arabia on 2012 – MERS-CoV

15. Laboratory Diagnosis
• The virus was identified by electron microscopy and confirmed by
growth in Vero cell culture, animal inoculation, cloning,
sequencing and histology
• RT PCR
• ELISA

16. Control
• No vaccine is currently available
• Strict isolation and quarantine

17. Chikungunya
• Virus first isolated from human patients in Tanzania in 1952
• The vector is Aedes aegypti
• No animal reservoir has been identified
• The name ‘Chikungunya’ was derived from native word for the
disease in which the patient lies doubled up due to severe joint
pain
• Epidemics have occurred in many African countries
• Virus first appeared in India in 1963, along with Dengue, caused
very extensive outbreaks in Kolkata, Chennai and other areas

18. Morphology
• Ribonucleic acid (RNA) virus that belongs to
the alphavirus genus of the family
Togaviridae
• Chikungunya virus is an enveloped plus-
strand RNA virus with icosahedral symmetry
• composed of repeating units of the E1 and E2
transmembrane glycoproteins (240
heterodimers of E2/E1 arranged as trimeric
spikes on its surface), the capsid (C), a host-
derived lipid bilayer, and a single molecule of
genome RNA

19. Chikungunya
• There are three major Chikungunya virus genotypes:
West African
East/Central/South African (ECSA)
Asian Genotypes
• The disease presents with a sudden onset of fever, crippling joint pain,
lymphadenopathy and conjunctivitis
• A maculopapular rash is common
• The fever is typically biphasic with a period of remission after 1-6 days

20. Chikungunya
• Detection of IgM or IgG in a paired serum sample by ELISA is the
mainstay of diagnosis
• RT-PCR can be used to detect viral RNA
• No vaccine is available