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Why Mosquitoes Are A Serious Threat

Mosquitoes can cause sickness and death through the diseases they can carry. We will discuss in detail mosquito borne diseases and which ones threaten us here in Louisiana both currently and potentially. Apart from disease mosquitoes also cause nuisance problems for rural home owners and ruin recreational activities such as hunting and outdoor sports. In extreme situations high levels of nuisance mosquitoes can pose a threat to livestock and wild animals as well. The economic impact of the problems that mosquitoes cause is staggering for such a tiny little insect. We will discuss this impact worldwide, nationally, and locally as well in this section on mosquitoes and the serious problems they cause. For even more information on mosquito borne diseases you can check out this article from AMCA.

 

Topic number one: Mosquito Borne Disease / Is it a problem?

  • According to the World Health Organization mosquitoes infect over 300 million people a year with Malaria and Dengue, just two of the life threatening diseases mosquitoes can carry.
  • According to WHO of those 300 million 800,000 will die from Malaria and another 20,000 from Dengue.
  • In Africa alone where mosquito control efforts are severely lacking businesses note that work absences related to mosquito borne diseases cost them $12 billion a year in lost productivity.
  • According to the CDC in the United States alone since 2001 over 30,000 people have been infected with West Nile Virus. Of those 30,000 infections 1,200 have resulted in death.
  • Excluding the cost of mosquito control efforts by governmental agencies the cost of WNV related health care alone in the US was estimated at $200 million dollars in 2002

Mosquito borne diseases in Louisiana: what you need to know!

 

 
West Nile Virus
  • Abbreviation: WNV
  • Threat status: current
  • Fatality rate: less than 1%
  • Primary mosquito vector: Culex Quinquefasciatus (Southern House Mosquito)
  • Potential mosquito vectors: Aedes Vexans, Aedes Aegypti, Aedes Albopictus, Aedes Triseriatus, Anopheles Quadrimaculatus, and Culex Salinarius.
West Nile Virus first arrived in the United States in 1999 in the New York area, since then it has spread rapidly covering virtually every part of the country. WNV most often starts out as a bird disease, it is then maintained and passed around from bird to bird in the wild by mosquitoes. Humans are infected when a mosquito that has fed on an infected bird then turns around and feeds on a human. WNV is not transmitted from human to human but rather from bird to mosquito to man, with man being an accidental or dead-end host. People over the age of 75 are at the greatest risk for succumbing to the severe form of the disease known as neuroinvasive WNV.

Most healthy persons who contract the disease will experience the less severe form of the disease known as West Nile Fever and make a full recovery. In 2002 there were 204 human cases in Louisiana 25 of which resulted in death. According to the CDC since 2001 Louisiana has recorded 654 cases of neuroinvasive WNV and 367 cases of West Nile Fever which has resulted in the deaths of 63 people. Since 2001 West Baton Rouge Parish had recorded 8 human cases and EBR has recorded 143. SInce surveillance began in earnest in 2004 WBR Mosquito Control has submitted 17,797 mosquito samples to LSU for testing. 1,609 have tested positive for WNV and several have tested positive for SLE as well. WNV looks like it is here to stay in Louisiana and is now officially considered endemic (native) to this state.

 

St. Louis Encephalitis

  • Abbreviation: SLE
  • Threat Status: Intermittent
  • Fatality rate: 3-30%
  • Primary mosquito vector: Culex Quinquefasciatus (Southern House Mosquito)
  • Potential Mosquito vectors: Culex Salinarius
Saint Louis Encephalitis is another arborviral disease found commonly in the United States. Much like West Nile Virus SLE is maintained in the bird population by mosquitoes with man being an accidental or dead end host. As with WNV man is infected when a mosquito that has fed on an infected bird also feeds on a human host. SLE can affect persons of any age however the effects are usually far more severe in those above 60 years old.

The most severe SLE epidemic in recent times was the one that rolled through the Mississippi River Valley in 1975. A total of 1,941 human cases were recorded 95 of which resulted in death. The most severe outbreak of SLE in Louisiana to date occurred in 2001. The outbreak which consisted of 70 cases happened in Ouachita parish and was centered in the city of Monroe. West Baton Rouge Parish recorded SLE positive mosquito pools both in 2006 and 2007 but no human cases.

Eastern Equine Encephalitis

  • Abbreviation: EEE
  • Threat Status: Intermittent
  • Fatality rate: 30%
  • Primary mosquito vector: Culiseta Melanura in birds / Culex Quinquefasciatus in man
  • Potential mosquito vectors: Cs. Inornata, Aedes Albopictus, Aedes Sollicitans, Aedes Vexans, Aedes Infirmatus, Aedes Atlanticus, and Coquillettidia Perturbans
Eastern Equine Encephalitis much like WNV and SLE is a viral infection maintained in the wild by a bird to mosquito to bird cycle. Horses are involved with man as dead end host meaning they cannot transmit the disease between themselves. Of the many mosquito borne diseases EEE is the deadliest mosquito borne disease to occur in the US with a 30% fatality rate for those infected. Half of those who survive the infection are stricken with various degrees of mental disability and paralysis. People younger than 15 and those older than 50 are the most prone to infection although EEE can affect persons of any age.

A major outbreak of EEE struck Louisiana in 1947 when the virus caused disease in over 15,000 horses and 15 human cases resulting in 7 people dead. Since that outbreak understanding of the transmission cycle in the wild and the creation of a vaccine for horses has resulted in much less infections for horses and humans. Although incidents of disease in humans has been low in recent times EEE still remains a deadly mosquito borne disease for both horses and man.

 

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