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. 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. Among the blood sucking species, only females suck blood as they need protein for the egg production. They also suppress the immune system of their prey. 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. The development from egg to adult mosquito varies from species to species and is strongly influenced by ambient temperature.
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.
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 per cent 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 is also increasing. This increase in the number of malaria cases in Pakistan is due to the floods, compelling millions of people to live in poor shelter and making ponds of water, an ideal breeding site for Anopheles mosquitoes.
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 nowadays, transmitted carried and spread by mosquitoes in the genus Aedes, which includes a number of mosquito species. 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.
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, $5 million. WHO has also provided 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 government 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.
The writer Dr. Naveed Iqbal is from Department of Veterinary Parasitology, University of Agriculture Faisalabad. He can be reached at <email@example.com>
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