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

(dr.naveeee@gmail.com)