A BIG DANGER BY A TINY CREATURE Dr. Naveed Iqbal, Dr. M. Sohail Sajid
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Transcript of A BIG DANGER BY A TINY CREATURE Dr. Naveed Iqbal, Dr. M. Sohail Sajid
A BIG DANGER BY A TINY CREATURE
Dr. Naveed Iqbal, Dr. M. Sohail Sajid
Surely you have listened a sentence about mosquitoes as, “they sing songs in the sleeping
person’s ear”, but actually mosquito is not a singer to sing songs. That is actually, shouting at
that time, saying that she has come to put the life of her victim by injecting the pathogen into the
victim’s blood. There are different receptors present in mosquito’s antennae and head which are
used in the detection of human scents up to 100 feet away. Study has shown that 72 acute
receptors are found in the antennae of the mosquitoes and almost 27 of them are used for
detecting the chemicals which are found in perspiration. Detected scents act as primary
indicators which mosquitoes follow to identify their prey. It has been observed that mosquitoes
are attracted towards five human scents as carbon dioxide (CO2), body odor, secretions, blood
type and lactic acid. Studies have shown that mosquitoes are more attracted towards the type “O”
blood and least towards the type “A” blood. Some selected persons also become their prey due to
the smell of their sweat which is due to the composition of CO2, Octenol and other compounds
responsible for making the body odor.
The mosquitoes belong to the family Culicidae. Out of all species, some are harmless or even
useful to humanity while others act as vectors and help in the transmission of different diseases
as they carry the pathogens responsible for the different diseases. They are active at dawn or
dusk but some species of Asian tiger mosquitoes feed on day time. Some species of mosquitoes
are not blood eaters and the other species those suck blood create a "high to low pressure" in the
blood to obtain it. Among the blood sucking species, only females suck blood as they need
protein for the egg production. This blood sucking becomes successful through the secretion of
anticoagulants, antiplatelets and vasodilatory substances in their saliva so that they can easily get
their meal. In addition, they also suppress the immune system of their prey. Most surprising
information about the feeding pattern of mosquitoes is that some mosquitoes of the genus
Toxorynchites do not feed on blood instead they are called as “Mosquito Eaters” as the larvae of
other mosquitoes are their prey. Biting nature of mosquito species is also different as some
species attack people in houses while others prefer to attack people walking in forests. Mosquito
passes through three stages (egg, larvae and pupa) during its life cycle to become an adult
mosquito. Breeding of mosquitoes occurs in the water which may be fresh water in the house or
stagnant water in the lakes. The development from egg to adult mosquito varies from species to
species and is strongly influenced by ambient temperature. Development can take 5 days in some
species and it may take up to 40 or more days in tropical conditions.
Over 3500 mosquito species have been identified, from which some species carry disease vector
responsible for human diseases and some for animal diseases becoming a source of zoonotic
infection. Mosquitoes are present around the globe except Antarctica. As far as the public health
is concerned, mosquitoes which are infected, transmit the infection from person to person and
most interestingly they do not exhibit any symptom themselves. Study on the various species of
mosquitoes has shown that they transmit a variety of diseases to more than 700 million people
annually in different parts of world like Africa, South America, Central America, Mexico,
Russia, and much of Asia, resulting in a death of millions of people.
According to an average estimation, two million people annually die of mosquito-borne diseases
and still the morbidity rate is many times higher. They act as vector for the transmission of
different parasitic, bacterial and viral diseases. A serious threat to human population by this
small creature is malaria which is caused by various species of Plasmodium. It is also distributed
due to the vector activity of genus Anopheles. Malaria is a leading cause of premature mortality
particularly in children under the age of five years. In rural areas of Pakistan, malaria is endemic
with two seasonal peaks, first in August which is milder vivax-malaria and second in October
which is potentially fatal falciparum-malaria. Annually, registered cases of malaria are more than
one million but 12% of people living in rural areas are carrying malaria parasite in blood without
showing malaria symptom. According to the ‘Disease Early Warning System’ of The World
Health Organization (WHO) and the Federal Ministry of Health Pakistan, the largest proportion
of suspected malaria cases has been recorded from the Baluchistan province. However,the
number of malaria cases from Punjab and Sindh provinces are also increasing. This increase in
the number of malaria cases in Pakistan is because of the floods, compelling millions of people
to live in poor shelter and making ponds of water, an ideal breeding site for Anopheles
mosquitoes. Lymphatic filariasis which is the main cause of elephantiasis is also spread by the
wide variety of mosquito species, characterized by great swelling of different parts of body and
about 40 million people are facing this problem worldwide. A bacterial disease named as
Tularemia, (Pahvant Valley plague, rabbit fever, deer fly fever, and Ohara's fever) which is
caused by Francis Ella tularemia is vectored by Culex and Culiseta genus. Viral diseases like
Yellow Fever, Chikunginya and Dengue Fever, a serious threat to the population now a days,
transmitted carried and spread by mosquitoes in the genus Aedes, which includes a number of
mosquito species. Of these species, the primary vector of the dengue virus is the species, Aedes
aegypti. It is the principal dengue vector responsible for dengue transmission and dengue
epidemics. Other mosquito species in the genus Aedes including Aedes albopictus, Aedes
polynesiensis, and Aedes scutellaris have a limited ability to serve as dengue vectors. Dengue
fever risk is not only restricted to the developing countries but also a great risk to the developed
countries. Severe dengue can be fatal and proper treatment is deadly needed after the quick
diagnosis. The three provinces, Khyber Pakhtunkhwa, Punjab and Sindh are facing the epidemic
of dengue fever. In Pakistan, the first confirmed outbreak of dengue fever was in 1994, but its
annual epidemic trend was confirmed in Karachi in November 2005. Due to which several
deaths occurred because of misdiagnosis, late treatment and lack of awareness. Pakistan has been
experiencing an epidemic of dengue fever since 2010 that has caused 16580 confirmed cases and
257 deaths in Lahore and nearly 5000 cases and 60 deaths reported from the rest of the country.
Other viral diseases like epidemic polyarthritis, Rift Valley fever, Ross River Fever, St. Louis
encephalitis, West Nile virus (WNV), Japanese encephalitis, La Crosse encephalitis and several
other encephalitis type diseases are carried by several different mosquitoes. Eastern equine
encephalitis (EEE) and Western equine encephalitis (WEE) occurs in the United States where it
causes disease in humans, horses, and some bird species. Because of the high mortality rate, EEE
and WEE are regarded as two of the most serious mosquito-borne diseases in the United States.
Pakistan's Ministry of Health’s Malaria Control Programme (MCP) is supported by The WHO,
as well as Health Cluster partners, for the prevention and controlling the malaria epidemic in the
country. For the prevention and control of malaria in the flood affected areas of Pakistan,
through WHO, the United States Agency for International Development (USAID) has donated,
US$ 5 million. WHO has also provide the rapid diagnostic tests and medical treatment while 5
million tablets of Primaquine have also been ordered. UK NGO, the International Health
Partners, has donated 600,000 Primaquine tablets which are enough to treat 18,000 people. In
2008, WHO ensured the collaboration with the Federal Ministry of Health for the prevention and
control of dengue along with the MCP. Another effort done by the Govt. against dengue is, First
Aid to Save a Life Pakistan which has comprehensive prevention and control management plans
against the dengue fever. Use of chemical sprays against dengue is also practiced but The
Environment Protection Department (EPD) does not recommend the use of chemicals as a
solution as this is causing a biodiversity loss.
No doubt, to prevent the spread of diseases or to protect the individuals from mosquitoes,
preventive measures should include vector control or eradication, prevention of diseases by using
prophylactic drugs and developing vaccines, prevention of mosquito bites by using insecticides,
nets and mosquito repellents, so that the minimum risk level can be achieved because we are
encountered by them, be their host and they give us gifts in the form of different infections.
Simply, “Beware of Mosquitoes”.
Dr. Naveed Iqbal
D.V.M, M.Phil.
Department of Veterinary Parasitology
University of Agriculture Faisalabad
Cell # 03317429180