Arthropod-borne
Virus Infections
1.
Many virus diseases are transmitted by the bite of an arthropod vector;
these viruses are called arboviruses, and multiply in the bodies of the
arthropod.
2.
Classification of Arboviruses
|
Family |
Virus |
Genome |
Virion
particle |
Virology |
|
Toga
(alphavirus): 37 viruses |
Eastern
& Western equine encephalitis |
Single-strand,
+ve polarity RNA |
Enveloped, 70nm |
Haemagglutinate
avian red cells. Grow
in cell culture. Pathogenic
for suckling mice. |
|
Flaviviruses:
> 70 viruses |
Dengue Japanese
encephalitis Yellow
fever |
Single-strand,
+ve polarity RNA |
Enveloped,
40-50nm |
Haemagglutinate Grows
in cell culture. Pathogenic
for suckling mice. |
|
Bunyaviruses:
nearly 300 viruses |
California
encephalitis Rift
Valley fever |
Single-strand,
-ve polarity RNA in 3 segments. |
Enveloped,
90-100nm |
Haemagglutinate Grows
in cell culture. Pathogenic
for suckling mice. |
3.
Clinical Features
a.
The arboviruses are transmitted via the bite of an insect vector
(mosquitoes, ticks and sandflies), acquiring virus from a natural host and
infecting humans by direct inoculation.
b.
Symptomless infection is common; main symptoms are fever, progressively
severe headache, nausea, vomiting, stiffness of neck, back and legs.
c.
Acute infections often progress to convulsions, drowsiness, deepening
coma, paralysis and tremor with high mortality (highest in Japanese, eastern
equine and Murray Valley encephalitis).
d.
Arboviral haemorrhagic fever is a generalized febrile disease, which may
be severe, with high fever, chills, sometimes headache, pain in the limbs,
nausea, vomiting, rash and arthritis.