3. RNA Viruses
All families of RNA viruses have an envelope, except(CHRP):
1. Caliciviruses
2. Hepatitis viruses (Except Hepatitis B, C)
3. Reoviruses
4. Picornaviruses
• Al families of RNA viruses have single stranded RNA EXCEPT for Reoviruses
have double stranded RNA.
All families of RNA viruses have nonsegmented RNA EXCEPT for Reoviruses
and influenza viruses have segmented RNA.
•
4. 5- Coronaviruses
Important Properties:
SARS-CoV-2 under electron microscope
• These are enveloped viruses with a helical nucleocapsid and a single-stranded
RNA viruses belonging to the Coronaviridae family.
• They have club-shaped spikes on the surface which give a crown (corona)-like
picture by electron microscopy.
5. Disease
• Coronavirus may be isolated from the nose and throat during the acute phase of
illness.
• In 2002, a new disease, an atypical pneumonia called Severe Acute Respiratory
Syndrome (SARS) emerged.
• In 2012, another severe pneumonia called Middle East respiratory syndrome
(MERS) emerged.
• In 2019, the SARS-CoV-2 causing a current pandemic of COVID-19 was
recorded.
6. Transmission & Epidemiology
• Coronaviruses are transmitted by the respiratory aerosol. Coronavirus
infections occur most frequently in late winter/early spring.
• SARS originated in China in November 2002 and spread rapidly to other
countries.
• Human-to-human transmission occurs, and some patients with SARS are
thought to be (super-spreaders).
• There are many animal coronaviruses, and they are suspected of being the
source of CoVID-19. The horseshoe bat appears to be the natural reservoir for
SARS-CoV-2.
7. • In 2012–2013, a new human
coronavirus caused an outbreak of
serious, often fatal pneumonia in
Saudi Arabia and other countries
in the region. The disease is called
Middle East respiratory syndrome
(MERS), and the virus is called
MERS coronavirus (MERS-CoV)
(also known as Camel flu).
8. • In December 2019, a pneumonia outbreak was
reported in Wuhan, China. On 31 December 2019,
the outbreak was traced to a novel strain of
coronavirus, which was first given the name
2019-nCOV by the World Health
• Organization (WHO) then they rename it as SARS-CoV-2. The Wuhan strain has been
identified as a new strain of Betacoronavirus from group ~70% genetic similarity to the
SARS-CoV. The virus has a 96% similarity to a bat coronavirus.
9. COVID-19 Fatality Rate by Pre-existing medical
conditions :
PRE-EXISTING CONDITION0
Cardiovascular disease
Diabetes
Chronic respiratory disease
Hypertension
DEATH RATE
10.5%
7.3%
6.3%
6.0%
Cancer
no pre-existing conditions
5.6%
0.9%
COVID-19 fatality rate in China 19
11. RNA Nonenveloped Viruses
Picornaviruses:
• They are small (20–30 nm) nonenveloped
viruses composed of an icosahedral nucleocapsid
and a single-stranded RNA genome. The genome
RNA has positive polarity (mRNA).
Poliovirus under electron micrograph
• The picornavirus family includes enteroviruses
which is a medically important group. Among the
major enteroviruses is poliovirus.
12. Poliovirus
Disease:
• This virus causes poliomyelitis. It is an acute infectious disease
that in its serious form affects the central nervous system
(CNS). The destruction of motor neurons in the spinal cord
results in flaccid paralysis. Symptoms also includes fever,
headache, myalgia, nausea, vomiting, signs of meningitis, and
pareses.
13. Transmission:
• There are three poliovirus serotypes (type1, type 2, and type 3); immunity to one
serotype does not produce significant immunity to the other serotypes
• The infection is spread by the faecal–oral route (through contaminated food and water).
The incubation period is usually 1–2 weeks. The patient can infect susceptible persons
from some days before illness and for one to several weeks after the illness. Children are
infectious for a longer period than adults. Humans are the only natural hosts.
Treatment:
• There is no antiviral therapy. Treatment is limited to symptomatic relief and respiratory
support, if needed. Physiotherapy as early as possible is important for the affected
muscles.
14. Prevention
• Poliomyelitis can be prevented by both the
killed vaccine (Salk vaccine, inactivated
vaccine, IPV) and the live, attenuated
vaccine (Sabin vaccine, oral vaccine, OPV).
Both vaccines induce humoral antibodies,
which neutralize virus entering the blood
and hence prevent central nervous system
infection and disease. At present, the
inactivated vaccine is preferred.
15. Reoviruses
• REO is an acronym for Respiratory Enteric Orphan; when the virus
was discovered, it was isolated from the respiratory and enteric tracts
and was not associated with any disease.
• Rotaviruses are the most important human pathogens in the reovirus
family.
16. ROTAVIRUS
Important Properties:
• Rotavirus has a segmented, double-stranded RNA genome surrounded by a
double-layered icosahedral capsid without an envelope. The rotavirus genome
has 11 segments. Under electron microscope the 70 nm diameter rotavirus viral
particles have a wheel-like appearance, prompting the name rotavirus, from the
Latin rota.
Rotavirus Structure
17. Disease
• Rotavirus is a common cause of viral
gastroenteritis, especially in children.
• The incubation period of the virus is 2 days and
the disease can last a week.
• Symptoms:
• Sever diarrhea
• Vomiting
18. Transmission:
• Rotavirus is transmitted by the fecal–oral
route.
Treatment & Prevention:
• There is no antiviral therapy. Only symptomatic
treatment. It is often necessary to correct the
patients’ fluid electrolyte balance.
Hospitalization may be necessary. Strict hygienic
measures are needed to avoid further spread.
19. Hepatitis viruses
• Many viruses cause hepatitis. Of these, five medically important
viruses are commonly described as “hepatitis viruses” because their
main site of infection is the liver.
• These five are hepatitis A virus (HAV), hepatitis B virus (HBV),
hepatitis C virus (HCV), hepatitis D virus (HDV, delta virus), and
hepatitis E virus (HEV).
• These are naked viruses (30 nm in diameter) with an icosahedral
nucleocapsid. They have single-stranded, linear, nonsegmented,
positive-polarity RNA (except HBV).
20. Hepatitis A Virus (HAV)
Important Properties:
• Hepatitis A virus (HAV) is a member of the picornavirus family genus
Hepatovirus.
• Hepatitis A has been called infectious hepatitis, epidemic hepatitis and short
incubation hepatitis. It has a single stranded RNA genome and a nonenveloped
icosahedral nucleocapsid. There is no antigenic relationship to HBV or other
hepatitis viruses.
21. Disease Symptoms:
Fever , Anorexia, Nausea, Vomiting, Jaundice, Dark
urine, Pale feces
Transmission:
HAV is transmitted by the fecal–oral route. Humans are the reservoir
for HAV. Children are the most frequently infected group, and
outbreaks occur in special living situations such as summer camps.
Unlike HBV, HAV is rarely transmitted via the blood.
Treatment:
No antiviral therapy is needed. Most cases resolve spontaneously in 2 to 4 weeks.
22. Prevention:
Active immunization with a vaccine containing inactivated HAV is
available. A combination vaccine that immunizes against both HAV
and HBV called Twinrix is available.
23. Hepatitis B Virus (HBV)
Important Properties
• HBV is a member of the hepadnavirus family.
Previously called serum hepatitis, post-transfusion
hepatitis and inoculation hepatitis. It is enveloped
with an icosahedral nucleocapsid core containing a
partially double-stranded circular DNA genome. The
envelope contains a protein called the surface
antigen (HBsAg), which is important for laboratory
diagnosis and immunization.
Hepatitis B virus under electron microscope
24. • Disease Symptoms:
• Many HBV infections are asymptomatic and are detected only by
the presence of antibody to HBsAg. The clinical appearance of
acute hepatitis B is similar to that of hepatitis A. However, with
hepatitis B, symptoms tend to be more severe, and life-
threatening hepatitis can occur.
• Transmission
The three main modes of transmission are via blood, during
sexual intercourse, and perinatally from mother to newborn.
The observation that needle-stick injuries can transmit the
virus indicates that only very small amounts of blood are
necessary. HBV infection is especially prevalent in addicts
who use intravenous drugs. Humans are the only natural hosts
of HBV. There is no animal reservoir
25. • Treatment:
• No specific treatment is required for acute hepatitis B since most
individuals will clear the infection spontaneously. For chronic hepatitis B,
entecavir (Baraclude) or tenofovir (Viread) are the drugs of choice. In most
patients when the drug is stopped, HBV replication resumes.
• Prevention
HBV infection is a preventable disease. Vaccination has been available since the early
1980s. Infants born to HBV-infected mothers should also receive HBV immunoglobulin
(HBIG), which is also recommended for postexposure prophylaxis. Interferon eliminates
viral replication in 40–50% of treated patients mostly. Response is usually permanent.
26. Hepatitis C Virus (HCV)
Important Properties:
• HCV is an RNA virus of the hepacivirus genus of the
Flaviviridae.
• It is enveloped containing a genome of single-stranded,
positive-polarity RNA.
• The genetic variation results in a “hypervariable” region in
the envelope glycoprotein.
• The genetic variability is due to the high mutation rate in
the envelope gene. As a result, multiple subspecies often
occur in the blood of an infected individual at the same
time.
27. • Transmission:
• Humans are the reservoir for HCV. It is transmitted primarily
via blood. Another major route of spread of this infection is
sharing of needles among intravenous drug abusers.
• The incubation time is approximately 7 weeks. Transmission
from mother to child during birth is another very common
mode of transmission.
• Disease Symptoms:
Malaise, Nausea, Vomiting, Fever, Anorexia, Jaundice, Dark urine,
Pale feces, Hepatomegaly, Splenomegaly, Cirrhosis or Hepatocellular
carcinoma.
Both HBV and HCV have significant roles in the development of
hepatocellular carcinoma that may appear many (15–60) years after
establishment of chronic infection.
28. • Treatment
• Interferon (alpha or beta) is the only treatment known with activity against HCV. Interferon
treatment reduces the chronicity rate in acute infection. The current standard of care for chronic
hepatitis C infection is a combination of peginterferon alfa-2a (Pegasys) and ribavirin. A 12
month course of this drug combination is effective in permanently eradicating infection in about
55% of cases.
• Prevention
HCV infection can only be prevented by avoiding contact with the virus. There is no vaccine
and the heterogeneity of the virus makes it difficult to develop a conventional vaccine in the
near future. There is no effective drug for prophylaxis following needle-stick injury; only
monitoring is recommended.
Patients with liver failure due to HCV infection can receive a liver transplant. Patients infected
with HCV and HIV should be prescribed highly active antiretroviral therapy (HAART).
29. Hepatitis D Virus (HDV, DELTA VIRUS)
Important Properties:
• HDV is unique single stranded circular RNA virus. It is a defective virus (i.e.,
it cannot replicate by itself because it does not have the genes for its envelope
protein).
• HDV can replicate only in cells also infected with HBV because HDV uses
the surface antigen of HBV (HBsAg) as its envelope protein. HBV is
therefore the helper virus for HDV.
30. Disease
• HDV causes hepatitis D (hepatitis delta). The symptoms are the same
as Hepatitis B. Patients coinfected with HDV and HBV is more severe
than in those infected with HBV alone.
• However, hepatitis in chronic carriers of HBV who become
superinfected with HDV is much more severe, and the incidence of
life-threatening hepatitis, chronic hepatitis, and liver failure is
significantly higher.
31. Transmission:
• HDV infection occurs only in HBV-infected patients. Most infected patients have acquired the
infection sexually or parenterally by sharing of needles.
Treatment:
• Treatment options for chronic hepatitis D are limited. Although α -inferferon is beneficial, it
requires high doses for long periods of time and relapse is common when the therapy is stopped.
Hepatitis B vaccine and passive immunoprophylaxis prevent HBV infection and thereby avoid
acute co-infection with HDV. However, other than avoiding risk-associated behavior, there is no
specific prophylaxis to avoid superinfection.
Prevention:
• There is no vaccine against HDV, but a person immunized against HBV will not be infected by
HDV because HDV cannot replicate unless HBV infection also occurs.
32. Hepatitis E Virus (HEV)
Important Properties:
• HEV is a nonenveloped, single-stranded RNA virus
classified as a member of the hepevirus family. Hepatitis
E virus is a newly identified agent causing epidemic
hepatitis, especially in Asia, Africa, India, and Mexico.
It has also been called enterically transmitted non-A,
non-B hepatitis.
33. Disease
• Clinically the disease resembles hepatitis A, with the exception of a high mortality rate in
pregnant women. Chronic liver disease does not occur, and there is no prolonged carrier state.
Transmission:
HEV is a major cause of hepatitis transmitted by the fecal–oral route, most likely
predominantly by way of contaminated drinking water. It is thought to be more common than
HAV in many developing countries.
Treatment & Prevention:
There is no specific therapy available. Reinfection is rare with circulating antibodies indicating
that antibodies to HEV protect against disease. However, to date no preventative effect of
immunoglobulins has been demonstrated. General hygienic measures, including boiling of
drinking water, can probably prevent infection
