************ PICORNAVIRUS ************
Characteristics
of the virus:
1.
They
are 18–30 nm in diameter and are icosahedral in shape.
2.
They
are positive stranded RNA viruses.
3.
It
causes disease ranging from CNS infection, febrile illness with rash,
conjunctivitis, herpangina, heart and lung infection to hepatitis.
4.
They
are the smallest RNA virus
Classification
of Picornavirus
Genus Main syndromes
Enterovirus Infection of the CNS,
skeletal muscles, skin and mucous membranes;
Hepatitis
A
Rhinovirus Common colds
Apthovirus Foot and mouth disease
Cardiovirus Encephalitis and
myocarditis in rodents
THE ENTEROVIRUS
Enterovirus infecting humans:
Group Number of serotypes
Poliovirus 3
Coxsackie A 23
Coxsackie B 6
Echovirus 31
Enterovirus 5
(numbered 68 – 72)
Disease associated with
Enterovirus:
1.
Poliomyelitis
a.
Incubation
period: 7–14 days
b.
Types
of illness produced:
(1) Minor illness due to viremia
(2) Major illness heralded by
meningitic phase. The onset of the illness is abrupt with headache, fever, and
vomiting and neck stiffness. Minor patients’ exhibits paralysis already. Paralysis
of the lower motor neuron type with flaccidity of affected muscles. In bulbar,
poliomyelitis, involvement of cranial nerves results in paralysis of the
pharynx bringing difficulty with respiration.
c.
Mode
of transmission: fecal–oral route
d.
The
poliovirus replicates in the lymphoid tissue of the pharynx and gut including
Peyer’s patches. The viremic phase brings lytic infection of neurons causing
paralysis. The anterior horn cells of the spinal cord are the worst affected
causing limb paralysis.
e.
Other
abnormalities produced:
(1) Inflammatory reactions
(2) Perivascular infiltration with
lymphocytes (cuffing)
(3) Microglial proliferation
(4) Edema
Syndromes caused by Coxsackievirus, Echovirus
and Enterovirus 70 & 71
Coxsackievirus Enterovirus
System affected A B Echovirus Type 70 Type 71
1.
CNS
a.
Meningitis + + + +
b.
Paralytic
disease + + + +
c.
Encephalitis + ++ ++ ++
d.
Encephalomyelitis
+
2.
Heart
/ Skeletal + ++ +
3.
GI
tract ++
4.
Respiratory
tract ++ ++ + +
5.
Skin,
mucous membranes
a.
Rashes
+ +
b.
Herpangina
++
c.
Hand,
foot & mouth
disease ++ + ++
6.
Conjunctiva
+ ++
7.
Pancreas +
8.
Perinatal
infection + ++ +
·
Type
72 is Hepatitis A
Laboratory diagnosis:
1.
Human
or monkey cell culture and observe for:
a.
Cytopathogenic
effect within 2–3 days
b.
Rounding
of cells
c.
Complete
destruction of monolayer
2.
Neutralization
test using LBM (Lim, Benyesh, Melnick) pool of reference sera. This contains
antibodies to some viruses but not others. By noting which pools do or do not
neutralize infectivity, it is possible to identify the virus in the specimens.
3.
Cell
culture inoculation in newborn mice of clinical specimens in which Coxsackie A
and B virus induce flaccid and spastic paralysis respectively.
4.
IgM
antibody test using ELISA
5.
Polymerase
chain reaction
Treatment, epidemiology and control:
1.
None
of the enteroviruses, including poliovirus is susceptible to chemotherapy and
there are no vaccines except for poliomyelitis. Control therefore depends on
hygienic measures:
a.
Proper
management of food, water supplies and sewage.
b.
Handwashing
and correct disposal or disinfection of potentially contaminated materials.
2.
Most
enterovirus survive well in moist or wet environments and are thus readily
transmitted via the fecal–oral route as described for polioviruses and are
therefore most prevalent in hot countries and during the summer months in
temperate zones.
3.
The
transmission of infections acquired by the respiratory or conjunctival routes
is facilitated by overcrowding.
4.
Most
infections are subclinical.
5.
Enterovirus
infections occur predominantly in children, some, particularly those of the
CNS, affect boys more often, or more severely, than girls.
6.
Epidemics
of some – but not all – enterovirus occur periodically.
THE HEPATITIS A VIRUS (HAV)
Characteristics of the virus:
1.
It
has a cubic symmetry and in 27 nm in diameter
2.
The
nucleic acid is a single stranded RNA with positive polarity
3.
It
has an incubation period of 2–6 weeks
Pathogenesis:
1.
Clinical
illness usually starts with few days of malaise loss of appetite, vague
abdominal discomfort and fever. The urine then becomes dark and feces pale.
2.
Jaundice
becomes apparent after the initial symptom, first in the sclera and then in the
skin; if severe, it may be accompanied by itching.
3.
The
patient starts to feel better within the next week or so and the jaundice
disappears within a month.
4.
HAV
first replicates in the gut; there is then a viremic phase during which,
presumably, the virus gets into the liver. Further replication in the
hepatocytes causes necrosis of these cells, which tends to be more pronounced
the center of the lobules. There is proliferation of Kuppfer and other
endothelial cells and are secondary periportal inflammations with mononuclear
cells.
************ REOVIRUS
************
Characteristics
of the virus:
1.
“REO”
stands for Respiratory Enteric Orphan.
2.
They
are wheel–like in appearance. The capsid has a double–shell and is 70 nm in
diameter, some smaller, single–shelled particles may also be seen. In most
virions a number of “spokes” radiate from a central “hub,” although some appear
empty by negative contrast staining. The cores appear to be icosahedral.
3.
They
differ from all other RNA viruses in that their genomes are double–stranded.
Electrophoresis of extracted RNA shoes that they are also divided into 10–12
segments of varying size, coding for a similar number of structural and
non–structural proteins.
4.
The
electrophoretic migration pattern of the nucleic acid differs between strains
and is used by some to define “electropherotypes,” which do not correspond with
the serotypes but which may be useful for epidemiological studies.
Two
genus of the Reoviruses:
1.
Rotavirus
a.
It
has an incubation period of 2–4 days; the characteristic syndrome comprises
vomiting, diarrhea and fever, but silent infections also occur. Dehydration
must be dealt promptly.
b.
It
primarily attaches the columnar epithelium at the apices of the villi of the
duodenum and upper ileum; the loss of these cells results in malabsorption.
Regeneration from the bases of the villi is normally rapid after the acute
attack.
2.
Orbivirus
a.
They
are transmitted from small rodents by ticks. They cause febrile illnesses,
often with meningitis or meningoencephalitis:
(1) Colorado tick fever
(2) Kemerovo viruses
Laboratory
diagnosis:
1.
For
rotavirus – trypsis treated monkey kidney cell culture.
2.
Test
for IgG
************ BUNYAVIRUS
************
Characteristics
of the virus:
1.
They
have a spherical particle containing single negative–sense RNA genome that is
segmented.
2.
They
have a lipid containing envelope and measures 90–100 nm. The envelope has two
glycoproteins in the lipid bilayer and surface projections (10 nm) of
glycopeptides clustered to form hollow cylinders.
3.
All
members of the family are arthropod–transmitted except for Hantavirus which is
rodent excreta transmitted.
The
four genus of Bunyaviridae:
1.
Orthobunyavirus
– California encephalitis, Oropouche fever
2.
Phlebovirus
– Sandfly (Phlebotomus) fever, Rift Valley Fever
3.
Nairovirus
– Crimean–Congo hemorrhagic fever
4.
Hantavirus
– Epidemic hemorrhagic nephropathy
Diseases
associated with Bunyavirus:
1.
California encephalitis
Characterized by severe bifrontal headache,
fever of 38–40oC, sometimes vomiting, lethargy and convulsions. Less
frequently, there is only aseptic meningitis.
Histopathological changes include neuronal
degeneration and patchy inflammation with perivascular cuffing and edema in the
cerebral cortex and meninges. This is transmitted by Aedes triseriatus and
small mammals such as squirrels and rabbits.
2.
Oropouche Fever
Characterized by febrile illness (especially
in Brazil). Three types of syndromes have been associated: febrile illness,
febrile illness with rash, meningitis or meningismus. Many patients become
severely ill, some to the point of prostration. The disease may be confused
with malaria or other febrile conditions. The incubation period varies from 4
to 8 days. Fever, chills, severe headache, myalgias, arthralgia, dizziness and
photophobia are the most common clinical manifestations. This is transmitted by
Culicoides paraensis (main vector) and Culicoides quiquefasciatus.
Two cycles of Oropouche virus:
a.
Jungle
cycle (vector unknown) – responsible for maintaining the virus in nature, where
primates, sloths and possibly certain species of wild birds are implicated as
vertebrate hosts.
b.
Urban
cycle – humans maybe infected and once infected, probably serve as an
amplifying host of the virus among hetophagus insects.
3.
Epidemic Hemorrhagic Nephropathy
This is spread via rodent excreta. The signs
are those of a viral hemorrhagic fever accompanied by renal pain and
proteinuria.
4.
Rift Valley Fever Virus – is the causative agent of Rift Valley
Fever, a viral disease that can cause mild to severe symptoms. The mild
symptoms may include: fever, muscle pains, and headaches which often last for
up to a week. The severe symptoms may include: loss of sight, beginning three
weeks after the infection, infection of the brain causing severe headache and
confusion, and bleeding together with liver problems which may occur within the
first few days. Those who have bleeding have a chance of death as high as 50%.
It is spread by either touching infected animal blood, breathing in the air
around an infected animal being butchered, drinking raw milk from an infected
animal or the bite of infected mosquite (Culex tritaeniorhynchus and Aedes
vexans).
5.
Crimean–Congo hemorrhagic fever
This is transmitted to human tick (Hyalomma
marginatum marginatum and Rhipicephalus sanguineus)
************ TOGAVIRUS AND FLAVIVIRUS ************
Characteristics
of the virus:
1.
The
virions are spherical and enveloped, 40–90 nm in diameter. The nucleocapsid has
icosahedral symmetry and contains a single molecule of positive–sense RNA.
2.
The
envelope contains one (flavirus) or two (togaviruses) E proteins that mediate
fusion of viral cellular membranes, releasing RNA into the cell cytoplasm; here
it functions as mRNA, directing synthesis of a single polyprotein that is
processed to form the structural protein of the virus.
3.
Togavirus
bud from the external plasma membrane of the cell in much the same was as
influenza viruses, whereas flavivirus but internally into cytoplasmic vacuoles.
4.
Both
viruses are arbovirus. Arbovirus is a term used to refer to a group of viruses
that are transmitted by arthropod vectors. The word arbovirus is an acronym (ARthropod–BOrne
virus). Symptoms of arbovirus infection generally occur 3–15 days after
exposure to the virus and last 3 or 4 days. The most common clinical features
of infection are fever, headache, and malaise, but encephalitis and hemorrhagic
fever may also occur.
Family
Disease
Vector
Flaviviridae Yellow
Fever Aedes
aegypti
Dengue
(4 Types) Aedes
aegypti
Omsk Ondatra
zibethicus
Japanese
Encephalitis Culex
tritaeniorhynchus
West
Nile Culex
tarsalis
Zika
Aedes
aegypti
Togaviridae O’nyong’nyong
Anopheles
funestus
Chikungunya
Aedes
albopictus
Ross
river Aedes
camptorhynchus
Diseases
associated with Flavirus and Togavirus:
1.
Dengue
Virus – is the causative agent of dengue fever. It is transmitted to human
Aedes mosquito. Five serotypes of the virus have been identified.
2.
Japanese
Encephalitis Virus – is the causative agent of Japanese Encephalitis. Domestic
pigs and wild birds (especially herons) are reservoir of the virus;
transmission to human may cause severe symptoms. Amongst the important vectors
of this disease are the mosquitoes Culex tritaeniorhynchus and Culex
vishnui
3.
West
Nile Virus – transmitted to humans by mosquitoes. The important mosquito
vectors vary according to geographical area; in the Eastern United States (Culex
pipens), in Midwest and West United States (Culex tarsalis) and in
Southeast United States (Culex quinquefasciatus)
4.
Yellow
Fever Virus – transmitted to human through the bite of Aedes aegypti.
Yellow fever is an acute viral disease. Symptoms include fever, chills, loss of
appetite, nausea, muscle pains particularly in the back and headaches. Symptoms
typically improve within five days. In some people within a day of improving,
the fever comes back, abdominal pain occurs and liver damage begins causing
yellow skin. If this occurs, the risk of bleeding and kidney problems is also
increased.
5.
Zika
VIrus – transmitted to human by Aedes aegypti and Aedes albopictus.
Symptoms may include fever, red eyes, joint pain, headache, and a maculopapular
rash. Symptoms general last less than seven days. Infection during pregnancy
causes microcephaly and other brain malformations in some babies. Infections in
adults have been linked to Guillain–Barre syndrome.
6.
Omsk
Hemorrhagic Fever Virus – transmitted to humans via contaminated water or an
infected tick. The main hosts of OHFV are rodents (Ondatra zibethicus).
7.
O’nyong’nyong
Virus – transmitted to human by bite of Anopheles funestus and Anopheles
gambiae. The name originated for the Nilotic language of Uganda and Sudan which
means “weakening of the joints.”
8.
Chikungunya
– transmitted to humans by the bite Aedes albopictus and Aedes
aegypti. Characteristics symptoms include sudden onset with high fever,
joint pain, and rash.
9.
Ross
River Virus – previously known to cause a disease known as “epidemic
polyarthritis.” It is transimitted to humans by Aedes camptorhynchus.
************ ARENAVIRUSES ************
These are
group of virus that infects rodents and occasionally humans. It is also been
discovered to infect snakes. The disease is transferred to human via rodents.
LCM viruses
Lymphocytic choriomeningitis (LCM) is a
rodent–borne viral infections disease that presents as aseptic meningitis,
encephalitis or meningoencephalitis. LCMV is naturally spread by the common
house mouse (Mus musculus). The virus seems to be relatively
resistant to drying and therefore humans can become infected by inhaling
infectious aerolized particles of rodent urine, feces or saliva, by ingesting
food contaminated with virus, by contamination of mucous membranes with
infected body fluids, or by directly exposing cuts or other open wounds to
virus–infected blood.
Lassa Fever
The primary animal host of Lassa virus is Mastomys
natalensis, an animal found in
sub–Saharan Africa which transmits the
disease to human through aerolized excreta. Lassa Fever occurs commonly in West
Africa. Outbreaks of the disease have been observed in Nigeria, Liberia, Sierra
Leone, Guinea and Central African Republic.
Junin virus
The causative agent of Argentine Hemorrhagic
Fever (AHF). AHF leads to severe compromise of the vascular, neurological and
immune systems and has a mortality rate between 20 and 30%. Symptoms of the
disease are conjunctivitis, purpura, petechial and occasionally sepsis.
The natural host of Junin virus are rodents,
particularly, Mus musculus, Calomys spp. and Akodon
azarae. Direct rodent–to–human transmission only takes place when a
person makes direct contact with the excrement of an infected rodent; this can
occur by ingestion of contaminated food or water, inhalation of particles in
urine or direct contact of an open would with rodent feces.
Machupo Virus
The vector is the vesper mouse Calomys
callosus, a rodent indigenous to Northern Bolivia.
Infected animals are asymptomatic
and shed the virus in excreta, thereby infecting humans.
The disease is known as Bolivian
Hemorrhagic Fever (BHF) or Black typhus or Ordog Fever.
************ CORONAVIRUS ************
The genomic
size of coronaviruses ranges from approximately 26 to 32 kilobases, the largest
for RNA virus. The name “coronavirus” is derived from the Latin “corona”
meaning crown or halo and refers to the characteristic appearance of virions
under electron microscopy with a fringe of large, bulbous surface projections
creating an image reminiscent of a royal crown or the solar corona. Most of the
coronaviruses produce respiratory syndrome.
Human coronavirus 229E
Human coronavirus OC43
SARS- CoV
Human coronavirus NL63
Human coronavirus HKU1
Middle East Respiratory Syndrome
coronavirus
************ RETROVIRUSES ************
Human T–lymphotropic virus
Causative agent of Adult T–cell
leukemia/lymphoma and HTLV–1 associated myelopathy / tropical spastic
paraperesis (HAM / TSP), a medical condition that causes weakness, muscle
spasms and sensory disturbance. Just like HIV, it is acquired by sexual
contact, blood transfusion, needle sharing and breast feeding.
Human Immunodeficiency Virus (HIV)
The causative agent of Acquired
Immune Deficiency Syndrome (AIDS). HIV is a member of the genus Lentivirus, part of
the Retroviridae family.
Human Foamy Virus (HFV)
HFV is a retrovirus and specifically belongs
to the genera Spumavirus. The foamy viruses derive their name from the
characteristic “foamy” appearance of the cytopathic effect (CPE) induced in the
cells.
************ ORTHOMYXOVIRUSES ************
Bourbon virus
A virus discovered in 2014 from a man from Bourbon
Country, Kansas, USA. It was caused by genus Thogotoviridae. It is transmitted
to human tick bite.
Influenza Virus B &
Influenza Virus C – causative agent of Viral Flu.
Quaranfil virus
Quaranjaviruses infect both arthropod and
vertebrate hosts. The most common arthropod hosts are species of soft–bodied
(Argasidae family) ticks. Most members cannot infect mosquito cell lines in the
laboratory. Infection in humans generally appears to be asymptomatic and has
occasionally been reported to be associated with mild fever.
************ PARAMYXOVIRUSES ************
Human Parainfluenza Virus (hPIV)
Human parainfluenza viruses commonly cause
upper and lower respiratory illness in infants and young children, but anyone
can get infected. After you get infected, it takes about 2 to 7 days before
symptoms develop. Symptoms of “upper” respiratory illness include: fever, runny
nose and cough. Symptoms of “lower” respiratory illness include: croup
(infection of the vocal cords, windpipe and bronchial tubes), bronchitis,
bronchiolitis and pneumonia. Young children are more susceptible to the
disease.
Human metapneumovirus
The second cause of lower respiratory
infection in young children. Compared with respiratory syncytial virus,
infection with human metapneumovirus tends to occur in slightly older children
and to produce disease that is less severe.
************ RHABDOVIRUSES ************
Rabies Virus
Caused by the genus Lyssavirus. Rabies virus
is a neurotropic virus that causes rabies in human and animals. Infection with
rabies virus is characterized by violent movements, uncontrolled excitement,
fear of water, inability to move parts of the body, confusion and loss of
consciousness. Once symptoms appear, the result is nearly always death.
************ ASTROVIRUSES ************
Astrovirus
Recognized to cause gastroenteritis in
children and adults. The main symptoms are diarrhea, followed by nausea,
vomiting, fever, malaise and abdominal pain. Some research studies have shown
that the duration of the symptoms are approximately three to four days. Astrovirus
infection is not usually a severe situation and only in some rare causes leads
to dehydration. Infected people do not need hospitalization because symptoms
reduce by themselves after a short time.
************ HEPEVIRUSES ************
Hepatitis E Virus
is transmitted by fecal–oral route. Although
Hepatitis E often causes an acute and self–limiting infection with low
mortality rates, it bears a high risk in developing chronic hepatitis in
immunocompromised patients with substantial mortality rates. Organ transplant
recipients who receive immunosuppressive medication to prevent rejection are
thought to be the main population at risk for chronic hepatitis E. Pregnant
woman, especially those in the third semester, suffers an elevated mortality
rate from the disease by 20%.
************ FILOVIRUSES
************
Ebola virus
Ebola Virus is known to cause severe and
often fatal hemorrhagic fever (Ebola Virus Disease) in human. The natural
reservoir of Ebola virus is believed to be fruit bats and it is primarily
transmitted between humans and from animals to humans through body fluids. Ebola
virus outbreaks tend to occur when temperatures are lower and humidity is
higher than the usual for Africa. Even after a person recovers from the acute
phase of the disease, Ebola virus survives for months in certain organs such as
the eyes and testes.
Marburg virus
Marburg Virus disease is clinically indistinguishable
from Ebola Virus Disease. The most important indicator that may lead to the
suspicion of MVD at clinical examination is the medical history of the patient.
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