Mosquitoes – Cont.1

Mosquitoes – How They Affect Humans(Cont.)

Diseases transmitted by mosquitoes

 During the prick, the mosquito releases some of its saliva to avoid coagulation of the blood. This is how the transmission of disease-causing agent takes place.

The females, vectors of various fatal diseases are from genera such as Anopheles spp, Aedes spp and Culix spp

 The diseases transmitted by the various vectors are:

1.    Malaria

Vector: Various of the 30 species of the genus Anopheles such as gambiae. In Europe the aim is to eradicate the disease in all over 50 countries by 2015, by eradicating the prevailing vector

Agent: Plasmodium, a protozoan microorganism: Most deadly specie is the Plasmodium falciparum;

Disease: Malaria, also called third-day fever, derived from the life cycle of the parasite. There are slight differences in the life cycle, some cause the fourth-day fever as they jump one full day.

2.    Dengue Fever

Vector: Aedes aegypti the principal vector, of secondary importance is de Aedes albopictus. All have white dotted lines along the body. This vector also transmits the Zika virus and the Chikungunya virus. Diseases new to the Americas since the year 2015 and 2013 respectively. Zika is named after the Zika forest in Africa, while Chikungunya comes from a word in the Makonde or Kimakonde language spoken by the Makonde, ethnic people from SE Tanzania and Northern Mozambique, meaning “bend over”.

This vector is closely associated with humans and their surroundings as they prey primarily on humans and breed in clean still water. This is often found in and around the house.

Agent: Dengue virus, which seems to have evolved around the beginning of the 19th century. There are four genotypes distinguished.

 Agent for Zika and Chikungunya are viruses with the same names respectively.

Disease: Dengue fever, also called fever of the joints. The hemorrhagic fever (DHF), is the most potent form, which often occurs when someone has antibodies of the virus from a previous infection. Risk factors for DHF are age below 12, female and Caucasians.
The Zika and Chikungunya diseases are in general mild fevers, with pain in the joints. Zika also may provoke a rash. and is serious in pregnant women, causing birth defect as microcephaly .

3.    Rift Valley Fever

Vector: Some five species of Aedes mosquitoes are a vector, together with some other bloodsucking insects. The disease can also be transmitted through contact with droppings of these insects and contact with body parts of infected and dead animals.

Agent: In 1977, the agent was recognized as of viral origin, caused by the genus Phlebovirus, one of the five genera in the family Bunyaviridae, .

Disease: This hemorrhagic fever infects humans and livestock alike. It was named “Rift Valley Fever”, after the Rift Valley in Kenya. The mortality rate in humans is around 1%. Severity in humans may vary from no or mild symptoms to serious liver necrosis. Normally patients recover within a week. A previous name is also veterinarian desease as this professional was very much at risk to contract the disease.

4.    Encephalitis

Vector: Aedes albopictus is the principal vector, While in Japan and various other East Asian countries the vector is Aedes japonicus. A sub-specie of the latter was found in the eastern states of the US near the end of the 20th century

Agent: The virus belongs to a group named Arbovirus, which has no taxonomic meaning but include three viral families of Togaviridae (main genus Alphavirus), Flaviviridae and Bunyaviridae. 

Disease: The agents cause various types of encephalitis such as that caused by West Nile Virus, St Luis encephalitis, La Crosse  encephalitis, Western Equine encephalitis, Eastern Equine encephalitis and Japanese encephalitis.

5.    Filaria

Vector: Dependent of locations around the entire world, various species of mainly Anopheles mosquitoes, but also species of Aedes and Culex mosquitoes are instrumental in the transmission of filarial agents.

Agent: Lymphatic filariasis is predominantly caused by the microscopic worm Wuchereria bancrofti, while in some Asian regions de agent also can be Bruchia malayi or Bruchia timori. 

De adult worm lives in the human lymphatic system. It can also affect domestic animals. The adult worms are mating in that habitat and produce millions of microscopic worms.

When the mosquito sucks the blood of an infected person the micro-filariae enter the body of that mosquito where it develops another stage. Later this mosquito can infect another person, the worms are quickly migrating to the lymph vessels.

Disease: The agents cause the disease called filaria and is spread from human to human via pricks of the mosquito.

As this disease may go on unnoticed for years, unless tested, it is often neglected, until malfunctions of the lymphatic system cause swellings of mostly the legs and sometimes other parts of the body. This may provoke bacterial infections in the lymphatic system and skin. In this stadium the disease is also called elephantiasis. The bacterial infections can be controlled by proper care.

A final note: for sake of completeness, need to mention that there also exist non filarial elephantiasis.

6.    Yellow fever

Vector: Two types of yellow fever are distinguished:

Jungle yellow fever, most spread by Aedes species amongst monkeys or humans, working in the jungle and

Urban yellow fever spread amongst humans and transmitted by the mosquito Aedes aegypti. These mosquitoes have a natural adaptation to live amongst humans. They breed in all forms of cavitations and containers holding water for a week or two.

Agent: The yellow fever is caused by a yellow fever virus, of the genus Flavivirus. It is spread through most of Sub Saharan Africa and tropical South America. The infections take place in both locations if the mosquito is also present.

Disease: Monkeys (primates) are the main holders of the disease.

If all urban conditions are favorable the disease may take epidemic proportions. At risk are young men, who are not vaccinated, visiting the jungle for leisure activities.

In older humans, immunity accumulates naturally. The mortality rate is ten times higher in Africa. BUT don’t take the chance and have a vaccination, before you go to infested areas. The health authorities in your country have the correct information.


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