Mosquitoes: More Than Just Irritating

Aedes_aegypti_feedingAedes egypti a day-biting mosquito

When we hear of diseases passed by mosquitoes the majority of people in the UK think they are safe, after all, we are hardly known for our tropical weather and balmy climate are we?

Down here in the far south-east it’s that windy it seems highly unlikely the irritating little bastards could maintain a flight path at all let alone one that allowed them to intercept a tasty human. WRONG!!!!!!

My fellow Southerners will back me up that down here these nasty, buzzing, biting monsters are so tough they wear hard hats and steel toe-capped boots. They seek you out the second you go into the garden and they bite, day and night, they care not as long as they get a feed.

The question is are we in the UK safe from the huge amount of diseases that mosquitoes can spread? Are we going to start experiencing outbreaks of the mosquito borne diseases that we usually associate with much more exotic climates?

The answer in my opinion is that it’s very likely.

More and more of us go away to ever more exotic locations for our holidays and many of the areas we visit are areas where mosquitoes and the diseases they carry are commonplace. Mossies coming back in luggage, hidden in clothing is a real possibility and there is no guarantee that the low temperatures in the aircraft hold will kill them off. The amount of clothes in a suitcase is ample insulation for something so small.

Our lifestyles at home also serve to bring more and more of us into contact with them. Fields particularly those with horse and/or livestock are mossie magnets. In fields with even a small amount of clay near the surface water doesn’t drain easily and it takes less than an egg cup of water to hatch out hundreds of mosquito larvae. They are prolific breeders and produce many thousands of offspring during their (thankfully) short lives.

Worryingly evidence from other parts of the world indicates that after a few dozen bites our bodies no longer produce a histamine response (the raised itchy bump a bite causes) Without that response to the anti-coagulant the mosquito injects to keep the blood fluid enough to suck up, we have no idea we have been bitten. A first thought might be that this is a good thing, but it really isn’t. Getting bitten and not knowing about it means we don’t associate any ensuing fever or sickness with the bite, and it causes a delay in getting treatment as well as a delay in diagnosis as mosquito borne diseases are not the first thing your average GP will consider when you present at the surgery.

Mosquitoes have no respect for international boundaries and I think we would all be very short-sighted to discount the possibility that we will start to see ‘home grown’ cases of the diseases they carry.

What follows is a list of mosquito borne diseases followed by a few basic tips on keeping them away. If anyone has any more feel free to post them in comments…summers coming we would all be very grateful.

There are several types of mosquito and a couple of those types have been in the news a good deal lately with the news coverage of Zika virus. Zika is a disease caused by mosquitos that has little effect on the primary host, usually mild flu-like symptoms at worst that pass off in a few days, but has grave implications if that host happens to be a pregnant woman. It can give rise to a condition called microcephaly, which in English means small head. Children born with microcephaly have misshapen heads and a smaller than normal, often under-developed brain. It can be severe enough to cause life-long impairment and the associated care needs that go along with that. You can read more about Zika here.

Malaria is the disease most often thought of when considering the damage mosquitoes can cause to humans, and we are all advised to take the tablets when we go on holiday to areas where malaria is endemic (widespread). There are several types of malaria spread by several types of mosquitoes and you can read about them here.

Although malaria is the most widely known disease that mosquitoes spread, and Zika is the disease is in the news, there are many more diseases that these loathsome creatures cause. To discuss each disease in detail is beyond the scope of this article, please click on the relevant (brown) links to find out more about a particular disease.

West Nile Virus was first reported in the United States in October 1999. You can read about that outbreak here.

Most cases of WNV are not serious and many people have no symptoms or only mild flu-like symptoms, such as headaches, muscle aches and a high temperature (fever).

Serious problems occur in fewer than 1 in 100 people infected with the virus, but can include infection of the brain (encephalitis), spinal cord, and tissues surrounding the brain and spinal cord (meningitis), which can be fatal.

Signs of a severe infection can include muscle weakness, disorientation, seizures (fits) and loss of consciousness.

Rift Valley Fever  originates, as you may expect, in the Rift Valley region that runs down East Africa from Kenya to South Africa. Primarily it affects cattle and livestock but is zoonotic which means it can and does infect humans as well as animals.

There is concern that RVF could spread to Europe and the United States as since 2000 cases have occurred outside of the African continent. Most human cases have mild symptoms very similar to those of West Nile Virus, but a small number of people will develop lesions in their eyes, meningitis or even haemorrhagic fever where spontaneous bleeding occurs from orifices as per Ebola. The death rate for these patients is 50% on average.

Dengue Fever is a leading cause of illness and death in tropical and sub-tropical regions. Symptoms include:

  • a high temperature (fever) that can reach as high as 41C (105.8F)
  • headache
  • pain behind the eyes
  • bone, muscle and joint pain

Like many of these diseases, the treatment is prophylactic to relieve the symptoms caused by the virus but treatment will have no effect on the virus itself. In 2013, there was an outbreak of Dengue in the UK with 541 cases reported. The same year saw over 2000 cases in Europe and major outbreaks with case numbers in the thousands in several Central American countries.

Complications that can lead to death include:

  • Hepatic failure
  • Encephalopathy
  • Myocarditis
  • Disseminated intravascular coagulation

Yellow Fever is a nasty disease that causes jaundice, a yellowing of the skin, hence the name. There is a vaccine available for yellow fever, it’s a live vaccine and it takes ten days to work. Some countries will not allow visitors in if they cannot produce a vaccination card.

Six travellers from Europe and North America have died from yellow fever since 1996. None of them were vaccinated.

The symptoms of yellow fever occur in two stages. The initial symptoms develop three to six days after infection and can include:

  • a high temperature (fever)
  • a headache
  • nausea or vomiting
  • muscle pain, including backache
  • loss of appetite

This stage will usually pass after three to four days and most people will make a full recovery.

However, around 15% of people go on to develop more serious problems, including jaundice (yellowing of the skin and whites of the eyes), kidney failure and bleeding from the mouth, nose, eyes or stomach (causing blood in your vomit and stools).

Up to half of those who experience these symptoms will die.(source)

Chikungunya is spreading fast. In the last few hours news articles have started to pop up concerning a major outbreak in Colombia, and meetings are taking place to strengthen the US response to the threat along the US-Mexican border. This outbreak started in the Caribbean late last year and has rapidly spread through South America and is marching north at a fast pace.

Infection with chikungunya virus is rarely fatal, but the joint pain seen with chikungunya can often be severe and debilitating. The virus is not spread between people. There is no vaccine and no specific treatment for the infection. Patients recover in about a week, although some people have long-term joint pain. Infection is thought to provide lifelong immunity. (source)

Eastern Equine Encephalitis (EEE) is spread to horses and humans by infected mosquitoes. It is among the most serious of a group of mosquito-borne arboviruses that can affect the central nervous system and cause severe complications and even death. EEE is found in freshwater hardwood swampland in the Atlantic and Gulf Coast states in the eastern part of North America, Central and South America, and the Caribbean. It has a complex life cycle involving birds and a specific type of mosquitoes including several Culex species and Culiseta melanura.

These mosquitoes feed on infected birds and become carriers of the disease and then feed on humans, horses and other mammals. EEE cannot be transmitted from humans or other mammals because the viraemia presented in the disease is not sufficient to further transmission. Thus, humans and other animals are known as “dead-end hosts.” Symptoms may range from none at all to a mild flu-like illness with fever, headache, and sore throat. More serious infections of the central nervous system lead to a sudden fever and severe headache followed quickly by seizures and coma. About half of these patients die from the disease. Of those who survive, many suffer permanent brain damage and require lifetime institutional care. There is no specific treatment. A vaccine is available for horses, but not humans.

St. Louis Encephalitis (SLE) is transmitted from birds to man and other mammals by infected mosquitoes (mainly some Culex species). SLE is found throughout the United States, but most often along the Gulf of Mexico, especially Florida. Major SLE epidemics occurred in Florida in 1959, 1961, 1962, 1977, and 1990. The elderly and very young are more susceptible than those between 20 and 50.

During the period 1964-1998 [35 years] a total of 4478 confirmed cases of SLE were recorded in the United States Symptoms are similar to those seen in EEE and like EEE, there is no vaccine. Mississippi’s first case of St. Louis Encephalitis since 1994 was confirmed in June 2003. Previously the last outbreak of SLE in Mississippi was in 1975 with over 300 reported cases. It was the first confirmed mosquito-borne virus in the United States in 2003. It turned up in October 2003 in California Riverside County in sentinel chickens. The last [SLE] human case in California occurred in 1997. In Louisiana in 2003 there was a fatal St Louis Encephalitis case previously listed as a West Nile caused death.

LaCrosse encephalitis (LAC) is much less widespread than EEE or SLE, but approximately 90 cases occur per year occurs in all 13 states east of the Mississippi, particularly in the Appalachian region. It was reported first in 1963 in LaCrosse, Wisconsin and the vector is thought to be a specific type of woodland mosquito (Aedes triseriatus) called the tree-hole mosquito, with small mammals the usual warm-blooded host. Infrequent fatalities occur in children younger than 16. It is not transmissible from human to human. There is no vaccine for LaCrosse encephalitis.

Western Equine Encephalitis (WEE) was first recognised in 1930 in a horse in California. It is found west of the Mississippi including parts of Canada and Mexico. The primary vector is Culex tarsalis and birds are the most important vertebrate hosts with small mammals playing a minor role. Unlike LAC it is nonspecific in humans and since 1964 fewer than 1000 cases have been reported As with EEE a vaccine is available for horses against WEE but not for humans. In Arizona 3 counties have been found with sentinel chicken flocks seroconverting to WEE.(source)

As more and more people travel the chances of these diseases making it to our shores increase. It should be remembered that many species of mosquito, such as those whose name is prefixed by Aedes actually bite during the daytime, not at dawn and dusk as most advice on avoiding bites states. If you are in an area where mosquitos are common the only way to be sure you won’t contract any of these diseases is to avoid getting bitten in the first place. Remember:

  • Mosquitos are more attracted to dark coloured clothing as heat is retained and they home in on that heat.
  • Avoid areas where there is stagnant water, and therefore, most likely to be mosquitos as they lay their eggs in water.
  • Keep your gardens and yards clear of standing water, however small the volume.
  • Mosquitos often stay within a few hundred feet of where they hatch. Preventing egg laying near your property reduces numbers drastically.
  • Find a repellent, natural or chemical based that suits you and the area you are in and apply when you are likely to come into contact with mosquitoes.
  • Mosquitos fly at under 25ft and are attracted to the carbon dioxide that we breathe out.

Thanks for reading,

Take Care

Lizzie

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