*Kanza Syed, Dr. Urfa Bin Tahir, Aleem Raza
* Department of Entomology, University of Agriculture, Faisalabad.
Corresponding Author Details:
Dr. Urfa Bin Tahir
When considering the life of the mosquito, we can say that it has a very
extraordinary adventure. It begins with a bite, a painless bite. The mosquito
comes in the night, alights on an exposed patch of flesh, and assumes the
hunched, head-lowered posture of a sprinter in the starting blocks. Then she
plunges her stiletto mouth-parts into the skin. The mosquito has long, filament
thin legs and dappled wings; she’s of the genus Culex (Cx), the only insect
capable of harboring the diseases in animals and humans. And she’s definitely a
she: Male mosquitoes have no interest in blood, while females depend on protein
rich hemoglobin to nourish their eggs. Female mosquito that bites an infected
human or animal can pick up pathogens along with the blood meal and can easily
pass to other non infected humans and animals. During pathogens pick and drop
service mosquito and pathogen does not harm each other but the pathogen
reproduces inside mosquito body.
Factors like ground water and their environs included: ponds filled by gutters
draining, grassy organic pools, borrow pits filled by irrigation or rain water,
drying irrigation water courses and temporary rain filled pools are positive
breeding habitat for mosquitoes. In Pakistan, the population dynamics of most
ground water breeding mosquitoes are dependent upon temperature, irrigation
practices, rainfall, with peak relative abundance occurring during the
pre-monsoon period. Among the major mosquitoes borne viral infections, west nile
virus (WNV) is an important threat to human and animal health. The virus exists
in nature primarily through a transmission cycle involving mosquitoes and birds
but sometimes also isolated from tick vectors (Argas, Hyalomma, and Ornithodoros).
Mosquitoes become infected with WNV when they feed on vertebrate hosts which are
mainly infected birds.
In humans, infection with WNV can cause clinical or subclinical symptoms.
Clinical symptoms vary from temporary fever to serious encephalitis (swelling of
brain). The disease can be severe in the elderly, but is usually mild in healthy
adults and children. The incubation period for WNV is 3-6 days and onset of
disease symptoms is usually sudden, beginning with a sustained, elevated fever.
Clinical infection can include severe headache; a rash, usually on the trunk;
and swollen lymph nodes. Symptoms of WNV infection can also include eye,
muscular and back pains, and gastrointestinal problems. In severe cases, there
are often symptoms of encephalitis with eventual neurological involvement and
sometimes death. Humans experience a low level of viremia that lasts about 6
days with 5 to 13 % mortality rate.
In animals, clinical signs of WNV infection have only been observed in equines
(horses, donkeys, mules and zebra), even though most equines infections are
asymptomatic and experienced 25% mortality. As with horses, cattle, sheep, and
camels can also be infected with WNV, but clinical symptoms and viremia capable
of infecting arthropod vectors have not been reported from these hosts. Birds,
however, do experience viremia capable of infecting arthropod vectors
(mosquitoes and ticks).
WNV is widely distributed in Asia, Africa, and America. However, worldwide
different ecological investigations suggested that WNV probably persists
naturally in bird populations with occasional transmission with infected
migratory birds to mammals of another region. In India members of the vishnui
complex (pseudovishnui, tritaeniorhynchus and vishnui) and perhaps Cx
quinquefasciatus are apparently important in transmission. Throughout the
distribution of WNV, low anthropophagic feeding patterns by the presumed vectors
have led several workers to suggest that Cx quinquefasciatus could be important
in transmitting WNV to man and other mammals.
In Pakistan, WNV has been isolated from febrile patients and pools of Cx
quinquefasciatus and "Cx tritaeniorhynchus" (possibly pseudovishnui +
tritaeniorhynchus) mosquitoes. The residents of several villages have
demonstrated a serological picture of endemic WNV exposure. Local strains of Cx
tritaeniorhynchus are highly susceptible to WNV in the laboratory; however, host
selection patterns in nature appear unsuitable for WNV maintenance in birds,
since over 90% of reacting blood smears reported to be positive for bovids.
An important question concerning WNV movement and transmission throughout
Pakistan is: What can be done to monitor the movement and introduction of WNV in
new cities and localities throughout Pakistan? The answer is simple:
surveillance, surveillance, surveillance, and more surveillance, and
surveillance mainly includes: vector surveillance, amplification host
surveillance, meteorological surveillance, and virus surveillance. Moreover,
mosquito and vector control programs throughout the Pakistan already have
considerable experience for dengue virus infection. Programs similar to this
should be considered for areas that are at high risk for arboviral transmission.
So, an accurate risk assessment of a vector borne epidemic will give all public
health authorities time to institute control strategies and public awareness
campaigns that will reduce the impact of an epidemic. Authorities should make
their decisions about what strategies to use based on scientific information
about the pathogen and vectors involved, and local or regional environmental
conditions. It is generally accepted that it would be enormously costly and very
difficult to vaccinate large human populations to prevent a vector borne
epidemic. However, vector control and personal protection against vectors and
the diseases they carry are the best way to avoid infection with vector borne
pathogens.
So, it is recommended to protect against biting arthropods, particularly when
they are infected with dangerous pathogens. Make sure screens are in good repair
to prevent mosquitoes from entering houses. If you must enter areas where there
is a threat of encountering infected mosquitoes, wear protective clothing.
Finally, use a personal insect repellent that provides a reasonable complete
protection time (CPT). The CPT is the total time following repellent application
that the treated individual will remain bite free. Unfortunately, Pakistan has
not good mosquito and arthropod control programs. However, in order to
efficiently cover the area of infections related to mosquitoes borne infections
try to reduce mosquitoes breeding sites; focal applications of insecticides
directed against adult and immature mosquitoes at breeding habitats and their
environs; public service announcements to educated residents about the vector,
the disease, and disease avoidance; tips help to prevent home invasion by
infected vectors; and information about the most effective means of personal
protection.