An insight into the RNA virus family Picornaviridae

1. PICORNAVIRIDAE
Submitted by-
Jagnoor Singh Sandhu
L-2021-V-48-M

2. HISTORY
• In 1897, Loeffler and Frosch demonstrated 1st
animal virus – FMD virus.
• In 1909, Landsteiner, Popper identified the
Poliovirus, the cause of human poliomyelitis.

3. CLASSIFICATION
• Picornaviruses are classes under Baltimore’s viral
classification system as group IV viruses as they contain a
single stranded, positive sense RNA genome.
• The family Picornaviridae originally comprises of atleast
eight genera: Aphthovirus, Enterovirus, Teschovirus,
Cardiovirus, Erbovirus, Kobuvirus, Hepatovirus and
Parechovirus.
• Four new genera viz., Tremovirus, Sapelovirus, Senecavirus
and Avihepatovirus, have recently been added.
• The former genus Rhinovirus was abolished in 2006, and the
member viruses human rhinovirus ( cause of common colds)
and two bovine rhinoviruses are included in the genus
Enterovirus.

4. VIRION PROPERTIES
• Picornavirus virions are very small, smooth and round
in outline,non-enveloped and have icosahedral
symmetry.
• The genome consists of a single molecule of linear,
positive sense, single stranded RNA.
• Both the 5’ and 3’ ends contain untranslated regulatory
sequences and has a covalently linked protein, VPg at
uncapped 5’ end and polyadenylated tail at its 3’ end.
• Genomic RNA is infectious. The capsid is constructed
from 60 copies of identical subunit each containing 4
capsid proteins : VP1 (1D), VP2 (1B), VP3 (1C) and
VP4 (1A) and a single copy of the genome linked
protein, VPg (3B).

5. Radial depth cued images of picornavirus particles
with a color gradient from innermost (dark blue) to
outermost (white) surfaces.
virus structure with different proteins
VP1 is the most external and immunodominant
of the picornavirus capsid proteins

6. VIRION STABILITY
• Most picornaviruses are relatively heat stable.
• Aerosols of aphthoviruses are less stable, but
may remain viable for several hours under high
humidity.
• They vary in their stability at low pH and such
differences were previously utilised to classify
them. Ex : Aphthoviruses are unstable below pH 7
whereas other picornaviruses are stable at acidic
pH 3.
• Because of differences in their pH stability, only
certain disinfectants are suitable for use against
each virus. Ex : Sodium carbonate 10% (washing
soda) is effective against FMD viruses.

7. VIRAL REPLICATION

8. Viral Proteins and their Functions

9. GENUS VIRUS DISEASE HOST
Aphthovirus Foot and mouth disease Foot and mouth Cattle, sheep, swine
virus disease ,goats, wild
ruminants
Equine rhinitis A virus Systemic respiratory Horses, camelids
disease
Bovine rhinitis B virus Mild respiratory Cattle
disease
Cardiovirus Encephalomyocarditis virus Encephalomyelitis
and myocarditis
Swine, elephants in
contact with rodents
Enterovirus Human enterviruses A, B, C Aseptic meningitis, Humans
and D poliomyelitis,
myocarditis
Human enterovirus C Poliomyelitis Humans
(Poliovirus)
Human rhinoviruses A,B and Respiratory disease Humans
C

10. GENUS VIRUS DISEASE HOST
Enterovirus Swine vesicular disease virus
Bovine enteroviruses (includes
bovine rhinovirus 1,3)
Simian enteroviruses
Porcine enterovirus B
Swine vesicular disease
Mild enteric and
respiratory disease
Asymptomatic infection
Asymptomatic infection
Pigs
Cattle
Primates
Swine
Erbovirus Equine rhinitis B virus Mild rhinitis Horses
Kobuvirus Bovine kobuvirus Enteritis Cattle
Teschovirus Porcine teschovirus 1 : PTV 1 Polioencephalomyelitis Swine
( TESCHEN/TALFAN
DISEASE)
Porcine teschovirus 2-11 Usually asymptomatic , Swine
mild diarrhoea,
pericarditis

11. GENUS VIRUS DISEASE HOST
Hepatovirus Hepatitis A virus Hepatitis A Humans
Tremovirus Avian encephalomyelitis
virus
Avian encephalomyelitis Chickens
Sapelovirus Porcine sapelovirus (PEV A &
PEV 8) along with PTV 1,3,6
SMEDI (Stillbirth,
mummification,
embryonic death and
infertility)
Pigs
Avihepatovirus Duck hepatitis A virus Duck viral hepatitis Ducks

12. FOOT AND MOUTH DISEASE
• It is a highly contagious disease of even-toed
ungulates and is characterized by fever and
vesicle formation on epithelial surfaces.
• It is listed under OIE list A disease and pose
significant economic losses.
• SYNONYMS :
- Aphthous fever
- Afta epizootica

13. ETIOLOGY:
• FMD is caused by foot and mouth disease virus of
the genus Aphthovirus of the family
Picornaviridae.
• There are seven serotypes ( identified by cross
protection and serologic test ) of FMDV :
O,A,C,Asia1,SAT1,SAT2 and SAT3.
• Within the serotypes there are many subtypes. For
epidemiological purposes,isolates of FMDV within
a given serotype are classified ( based on VP1
gene) according to their topotype.
• Ex: For serotype O, there are atleast 7 topotypes,
reflecting its wide geographic occurrence from
South America across Africa to Southeast Asia.

14. HOST AND DISTRIBUTION
• FMD affects a wide variety of cloven – footed
domestic and wild animal species.
• Cattle, water buffalo, swine, sheep, goats, camels and
many wild ruminants are susceptible.
• Horses are refractory to the infection.
• Clinical signs are most severe in cattle and swine.
• FMD is widely distributed throughout the world and
the infection is still enzootic in much of Africa, Asia
and the Middle East.
• In India, O, A, and Asia 1 serotypes are prevalent.
• Serotype C was found in Philippines in 1976-1981,
1983-1990, & in 1994

15. DISTRIBUTION
SEROTYPES GEOGRAPHIC DISTRIBUTION
O, A, C South America, Eastern European countries
O, A, C, SAT 1, 2 and 3 Africa
O, A, C, Asia 1 Asia

16. TRANSMISSION
• FMD is spread rapidly by movement of infected animals.
• The main mode of transmission is through the inhalation of
droplets.
• But, direct or indirect contact with affected animals
• Ingestion of infected food.
• Mechanical transmission by contaminated objects (clothing,
hands, footwear, vehicles).
• Inoculated with contaminated vaccines and veterinary
instruments.
• Insemination with contaminated semen and so on can all
produce infection.
• Long distance spread is dependent on wind direction and
speed and is favored by low temperature, high humudity and
overcast skies.

17. TRANSMISSION
Reasons for the rapidity of spread:
• The highly infectious nature of the virus.
• The rapid replication cycle with very high virus yields.
• Production of high-titer virus in respiratory secretions.
• Large volumes of droplets and aerosols of virus shed
by infected animals.
• The stability of virus in such droplets.
• The short incubation period.
• The excretion of virus before 24 hours of onset of
clinical signs results in rapid virus dissemination.
• The involvement of sheep or other animals that show
minimal signs of infection may also contribute to rapid
spread.

18. PATHOGENESIS

19. CLINICAL FEATURES
CATTLE:
• Incubation period – 2 to 8 days.
• Mortality is low; morbidity – 100%
• Pyrexia (39.4 – 40.6 ⁰C), anorexia and depression.
• Marked decrease in milk yield and abortion due to pyrexia.
• Drooling of saliva.
• Vesicle formation ( tongue, dental pads, gums, soft palate,
nostrils, interdigital space, coronary bands and teats.
• Rupture of vesicles – crater like lesions producing
characteristic smacking sound.
• Calves upto 6 months of age – die from acute myocarditis.
• Complications of FMD lesions – superinfection of lesions,
hoof deformations, mastitis, permenant impairment of milk
production, permenant weight loss and impairment of
thermoregulatory mechanism (“PANTERS”).

20. LESIONS
• Vesicles in buccal and foot areas.
• Fluid filled vesicles – enlarge and coalesce
with adjacent ones – rupture and slough
leaving an eroded area which is covered with
gray fibrinous coating.
• Degeneration and necrosis of myocardium –
“tigeroid heart”.

21. A B
C
A, B – Drooling of saliva
C – Foot lesions may cause shifting
of weight to front legs; reluctant
to move and have a hunched back

22. A
B
C
A – Ruptured vesicles on tongue
B – Ruptured vesicle on upper gums
and muzzle
C – Ruptured vesicles in
the interdigital space

23. A
C
A – Vesicles on the teat
B– Tigeroid heart appearance in heart
C – “Hairy panters” (complications of FMD)
B
A

24. CLINICAL FEATURES
PIGS:
• Lameness is often the first sign of FMD.
• Foot lesions may be more severe and painful.
• Vesicles within the mouth are not common, although
common on the snout.
• No drooling of saliva.
• Abortion and suppuration of denuded areas resulting in loss
of claws and prolonged lameness.
• Other signs: fever, anorexia, reluctance to move, vesicles on
coronary band, interdigital space, and snout.
LESIONS:
• Detached hoof, tigeroid appearance of myocardium.

25. A
B
A – Vesicles on the snout
B – ruptured vesicles in the
interdigital space and coronary band

26. DIAGNOSIS
• FIELD DIAGNOSIS:
• Based on characteristic clinical signs and lesions. Whenever salivation and
lameness occurs simultaneously with vesicular lesions FMD should be
suspected.
• VIRUS ISOLATION AND IDENTIFICATION:
• Clinical materials:
-In early infection: vesicular fluid, epithelial tissue from the edge of
recently ruptured vesicles, blood (in anticoagulant), milk and serum
samples.
-In more advanced cases: Oesophageal/pharyngeal fluids (from
ruminants), pharyngeal swabs (from swine) are ideal from animals in
convalescent stage.
-Dead animals: Tissue samples from lymph nodes, thyroid, adrenal gland,
kidney and heart. Should be sent within 24 hrs to the laboratory or should
be frozen -70⁰ C and sent.

27. DIAGNOSIS
Virus isolation:
• Cell cultures: The virus grows well in cell cultures.
Primary cultures of bovine, porcine or ovine kidney
and primary bovine thyroid cells are more sensitive
than established cell lines such as baby hamster
kidney (BHK-21) or pig kidney (IB-RS-2) cells. CPE
( rounding and flattening of the cells, breaking down
of the intracellular bridges and finally cell death) are
produced typically in 24-48 hrs.
• Laboratory animals: Unweaned mice (2-7 days old)
are commonly used for cultivation of FMDV.
• Virus identification: The isolated virus can be
identified by ELISA, RT-PCR or neutralization test.

28. CPE in FMDV-infected cells. Still images from a live-cell experiment in which BHK-21 cells were
infected with FMDV as shown up.
Normal BHK-21 cell line

29. DIAGNOSIS
IMMUNOLOGICAL METHODS OF VIRUS IDENTIFICATION:
• ELISA: Is preferred test for detection and identification of FMDV
serotypes. It is more sensitive than CFT and is not affected by
complementary factors.
NUCLEIC ACID DETECTION METHODS:
• RT-PCR: Can be used to identify specific serotypes of FMDV. In
situ hybridization
SEROLOGICAL TESTS:
• VNT and ELISA are prescribed tests for international trade and are used
for detection of specific antibody response against FMDV.

30. PREVENTION AND CONTROL
• Immunity is not considered life-long. Recovered animals can be
infected immediately with other serotypes.
• Frenkel method: In this method of vaccine production, the normal
tongue epithelium is removed, minced, placed in a nutrient broth
and inoculated with FMDV. After replication, the virus is
inactivated with formalin and adjuvanted with aluminium
hydroxide.
• At present, instead of tongue epithelium, BHK-21 cell lines are
used. Formaldehyde, Binary ethyleneimine (BEI) is used as
inactivating agent and aluminium hydroxide-saponin or oil is used
as adjuvant. Protection for 4-6 months.
• Though molecular vaccines are available, they are not much
effective and not economical.
PUBLIC HEALTH SIGNIFICANCE:
- Rarely zoonotic with often subclinical infection. Clinical signs
include pyrexia, anorexia and vesiculation.

31. Vaccination Schedule

32. SWINE VESICULAR DISEASE
• Swine Vesicular Disease (SVD) is mild vesicular disease of
pigs.
• This was first described in Italy in 1966 and still occurs as
endemic.
• This may occur sporadically in European and Asian
countries.
ETIOLOGY:
• It is caused by swine vesicular disease virus (genus.
Enterovirus).
• The pig is the natural host for the virus.
• The virus is resistant to low pH and temperatures, hence
transmitted easily between countries in affected meat.
• Pork products prepared without heat treatment (such as
salami) can harbor virus for several months.

33. TRANSMISSION
• Direct or indirect contact:
- Infected animals or faeces
- Contaminated environment
• Ingestion:
- Contaminated meat scraps
• Virus excretion:
- Nose, mouth, faeces
- Up to 48 hrs. before clinical signs

34. PATHOGENESIS
Vesicles contain high titers of virus and virus in large quantities is excreted in the faeces
(upto 2 months after infection). Carrier status is been detected rarely.

35. CLINICAL FEATURES
• IP: upto 7 days.
• Disease is often detected by the sudden appearance of
lameness in several pigs in a herd.
• Affected pigs show transient fever, dullness,
inappetance and vesicles appear at the junction
between the heel and coronary band and then spread to
encircle the digit.
• Less commonly lesions are found on the snout, lips and
tongue.
• Occasionally, some infected swine develop signs of
encephalomyelitis, such as ataxia, circling and
convulsions.
• Subclinical disease is more common.

36. Vesicles on snout and heel

37. DIAGNOSIS
• Based on symptoms and lesions. But
laboratory diagnosis is essential to distinguish
the vesicular diseases.
Disease/Virus Susceptible animals Resistant species
FMD Cattle, sheep, goat and pigs Horse
Swine vesicular disease Pigs Cattle, sheep, goat and
horse
Vesicular exanthema of
pigs
Pigs Cattle, sheep, goat and
horse
Vesicular stomatitis Cattle, pigs and horses Sheep and goat

38. DIAGNOSIS
• Clinical materials: Vesicular fluid or epithelium,
blood and serum.
• Virus isolation:
- Cell culture: SVD virus grows well in pig kidney
cells and produce CPE as early as 6 hrs.
- Laboratory animal: Isolated by the intracerebral
inoculation of newborn mice, which develop paralysis
and die.
- Virus identification: ELISA can be used to detect Ag.
• Nucleic acid detection methods: RT-PCR tests and
real time RT-PCR.
• Serological tests: VNT and ELISA are commonly
used test.

39. Prevention and Control
• Preventive measures include screening imported pigs,
restricting the importation of pork products that may contain
virus, restricting swill feeding, and regulating the disposal of
garbage from international airplanes and ships. Some
countries conduct routine surveillance and pre- and post-
export testing, particularly in Europe.
• No commercial vaccines are available. Outbreaks are
controlled by quarantining infected farms and regions,
tracing pigs that may have been exposed, culling infected and
in-contact pigs, and cleaning and disinfecting the affected
premises.

40. AVIAN ENCEPHALOMYELITIS
• Synonym: Epidemic tremors.
• Avian encephalomyelitis (AE) is an economically
important disease of young chicken.
• It is placed under the new genus, Tremovirus and
is closely related to Hepatitis A virus.
• Transmission:
- Main mode transmission is by fecal-oral route.
- Vertical transmission via the egg may also occur.
- It produces enteric infection and the virus is
shed in feces.

41. CLINICAL FEATURES
• Occurs in chickens – 1 to 21 days of age.
• IP: 1 to 2 days after vertical transmission and 11 days
after horizontal transmission.
• Characterized by dullness, progressive ataxia, tremors
(particularly of the head and neck), weight loss,
blindness, paralysis and in severe cases, prostration,
coma and death.
• Recovered birds show CNS disorders.
• Eggs from infected layers show a reduced hatchability
and increased loss of hatched chicks.
• It causes relatively mild encephalomyelitis in quail,
turkeys, pigeons and pheasants.

42. LESIONS
• No obvious macroscopic lesions.
• Lesions of viral encephalitis seen throughout
the CNS, microscopically.
• Non-suppurative encephalomyelitis and
lymphocytic accumulation are characteritic.
• Central chromatolysis of neurons in the
medulla oblongata is strongly indicative of AE.

44. DIAGNOSIS
• Based on the clinical signs and histopathologic lesions.
• Clinical materials: Tissues such as brain, pancreas and
paired sera.
• Virus isolation may be done in cell culture, embryonated
eggs via yolk sac route (5 – 7 days old) and virus
identification by immunofluorescence staining of tissues
from affected chicks.
• Nucleic acid detection methods by RT-PCR.
• Serological tests by ELISA using purified or recombinant
antigens are commonly used.
CONTROL:
• Can be achieved by either depopulation or vaccination.
• Attenuated virus vaccines administered in the drinking water
are available.( after 8 weeks of age, but at least 4 weeks
before the onset of egg laying).

45. Precautions
• In accordance with the WOAH, all susceptible birds on site
should be vaccinated concurrently with the dose
recommended by the manufacturer.
• Administration of live AE vaccine to flocks may result in a
transient decrease in egg production for up to 14 days.
• Do not administer live AE vaccine to breeders within 4 weeks
of onset of lay or during egg production. The AE virus is shed
in faeces and transmitted vertically in eggs for up to 4 weeks
following vaccination.
• To avoid clinical AE in the progeny, eggs for hatching should
not be taken from the flock until 4 weeks have elapsed
following vaccination.
• Birds less than 8 weeks-of-age exposed to live AE vaccine
may display clinical neurological disease.

46. Vaccination
AE-Poxine is recommended for the prevention of
avian encephalomyelitis and fowl pox to healthy
pullets between the ages of eight weeks and four
weeks before the start of egg production. Store this
vaccine at not over 45°F (7°C). Do not vaccinate
within 21 days before slaughter.
Vaccine administration
Live AE vaccine - drinking water or wing web
from 10 weeks-of-age until 4 weeks before
onset of lay.

47. DUCK VIRAL HEPATITIS
ETIOLOGY:
• Duck hepatitis virus 1 is the most common. Classified under
the new genus, Avihepatovirus of the family Picornaviridae.
• Duck hepatitis viruses 2 and 3 are now classified as
astroviruses (genus Avastrovirus of the family Astroviridae).
TRANSMISSION:
• Highly contagious and the virus is excreted in feces.
• The infection is transmitted by either direct contact or
through fomites.
• Rats have been described as reservoir.
• Introduced into susceptible population through duck meat
products.

48. CLINICAL FEATURES AND
LESIONS
• IP: 1-5 days.
• Common in ducklings less than 21 days.
• Clinical signs: stand still with partially closed
eyes, loss balance so that fall to one side,
paddle spasmodically and die.
• Mortality may reach 100%.
• Lesions : Hepatomegaly, edematous, mottled
with punctate or ecchymotic hemorrhages.
Extensive hepatic necrosis.

49. (A,C) Signs of opisthotonos and spasmodic kicking. (B,D) Non-infected Pekin and
Muscovy controls showed normal liver appearance. (E,F) Hemorrhagic spots on the
liver surface of Pekin ducklings. (G,H) Muscovy livers showed severe congestion.

50. DIAGNOSIS
• Based on the history, clinical signs and characteristic necropsy
findings.
• Clinical materials: Liver is the ideal material.
• Virus can be isolated in duck hepatocyte cultures/duck embryo
liver. DHAV-1 produces CPE characterized by cell rounding.
Virus identification by immunofluorescence staining.
• Nucleic acid detection methods: RT-PCR
• Serological tests: VNT has been developed.
• Control:
- Recovered ducks are immune. Hyperimmune serum reduces
losses during outbreaks.
- Attenuated virus vaccines are available commercially.
- Inactivated vaccines against DHAV-1 can also be used to prime
the ducks to produce high antibody titre.

51. Prevention & control
• DHAV-1 infections can be controlled by the use of live
attenuated virus vaccines and an inactivated virus vaccine.
They are administered to breeder ducks to confer passive
immunity to ducklings.
• Ducklings susceptible to DHAV-1 may be passively protected
with a chicken egg yolk antibody preparation. DAstV-2
infections can be controlled by the use of a live attenuated
virus vaccine given to breeder ducks to confer passive
immunity to ducklings.
DVH type II is caused by duck astrovirus type 1 (DAstV-1)
• Control is based on vaccination and biosecurity.
• There is no specific treatment for duck viral hepatitis infection.
Prevention and control is based on strict biosecurity and
implementation of vaccination protocols.

52. • REFERENCES:
- Fenner’s veterinary virology – 5th edition.
- Veterinary virology by Frederick A. Murphy –
3rd edition.