West Nile virus was first discovered in 1937, in the West Nile area of Uganda, in East Africa. (This is how the virus got its name.) However, before the 1990s, there were very few cases of WNV. Then there was an outbreak in Algeria in 1994 and another in Romania in 1996. By 2004, the virus had spread to North America, the Caribbean islands, and Latin America. It continues to spread through Africa, Asia, Australia, Europe, the Middle East, Canada, and the United States. In 2012, one of the worst West Nile virus epidemics yet happened in the United States; 286 people died.
About 80% of people who get West Nile virus have no symptoms.
When a person does get symptoms, they usually do not appear until 2 to 15 days after the person got the virus. (This is called the virus's incubation period.)
West Nile virus can cause many different types of illness. The rarest, but most serious types affect the neurological system - the brain and the nerves. The most common type of illness caused by WNV is West Nile fever, which does not affect the neurological system.
West Nile fever happens in about 20% of people with WNV. It causes a high fever and flu-like symptoms. Usually, the symptoms are not too bad, and get better after 3 to 6 days. Symptoms may include:
Neuroinvasive disease is when the West Nile virus infects the central nervous system (the brain and spinal cord). This happens in less than 1% of people who get West Nile virus. However, in those people, it can cause very serious problems. These problems include:
WNV can cause some other complications that do not affect the neurological system. These complications are very uncommon. They include:
At first, a medical professional usually makes a possible diagnosis of West Nile virus based on a person's symptoms, where they live, and when and where they have traveled. The World Health Organization says that doctors should suspect West Nile virus if a patient:
West Nile virus can be diagnosed for certain by:
There is no known treatment or cure for WNV. There are no known anti-viral medications (medicines which kill viruses) which will kill the West Nile virus. Doctors can only provide "supportive care," which means they can only treat the symptoms of WNV. For example, they can give fluids through a needle placed into a vein if a person is very dehydrated; help the person breathe if needed; and give medications to prevent them from getting any other infections.
The West Nile virus stays alive in nature by getting spread back and forth between birds and mosquitoes. Birds get WNV more often than any other living things. When a mosquito bites a bird that has WNV, the mosquito gets the virus. Then, if the mosquito bites a bird that does not have WNV, the mosquito can give that bird the virus. In this way, birds and mosquitoes give the virus to each other and keep it alive.
Humans usually get West Nile virus by being bitten by mosquitoes who have gotten the virus from birds. Humans can get the virus from many different species of mosquitoes.
Though this is not common, a person with West Nile virus can give another person the virus. This can happen if:
In contrast to the 4 currently available West Nile Virus vaccines for horses, there is no human vaccine available to prevent West Nile virus infection. Six vaccines have been trialled in humans with the most successful only proceeding to Phase II trials. The best way for people to protect themselves against West Nile virus is to protect themselves against mosquitoes. There are many ways to do this. For example:
Scientists can trap mosquitoes and birds, and test them for West Nile virus to see if the virus is spreading in a certain area. If it is, they can do things like spray pesticides to kill mosquitoes.
About West Nile virus
Prevention
For medical professionals
3rd millennium
The 3rd millennium started on January 1, 2001 and will end on December 31, 3000.
Century leap year
In the Gregorian calendar, a century leap year is a year that is exactly divisible by 400 (and qualifies for the adding of February 29, like all other leap years). If a year is divisible by 100 but not 400, it is a common year (not a leap year). For example, the years 1600 and 2000 were century leap years; the century years 1700, 1800, and 1900 were common years, as will be for 2100, 2200, and 2300. The next century leap year will occur in the year 2400. Century leap years always begin on a Saturday, and February 29 always falls on a Tuesday.
The start days of exceptional common years (century years not evenly divisible by 400) also varies; the century year begins on a Friday if the remainder obtained by dividing it by 400 is 100, Wednesday if the remainder is 200, and Monday if the remainder is 300.
The Gregorian calendar more accurately tracks Earth's revolution around the Sun, more so than the older Julian calendar, in which every fourth year (including end-of-century years) is a leap year. Because of this, the Julian calendar began to gradually drift with respect to the four seasons. Each season has been occurring earlier and earlier over time. Therefore when the Gregorian calendar was created in 1582, it eliminated this problem by specifying that end-of-century years are only leap years if divisible by 400.
Plywood
Plywood is a manufactured wood which is made by gluing several thin sheets of wood together with the grain alternately running along the sheet then across it.
The veneer is usually about 3 millimetres thick for each layer. Interior layers of these boards are usually made from an inexpensive wood while the outer veneer layers are made from more expensive timber to give the board a nice wood grain appearance. The glued layers are heated together to make the seal become better bonded.
A common reason for using plywood instead of plain wood is its resistance to cracking, shrinking and changing shape. It is cheaper and stronger than most plain woods.
It is used to make a range of things from sheds, to cladding to cabinets. It is graded on the quality, from class A to class D, A being the best quality and D being the worst quality.
Different kinds of plywood are made for different purposes. Marine plywood, for example, is especially resistant to water. There is a world-wide industry making plywood for structural purposes. IKEA is well-known for using mostly plywood and chipboard in their indoor and outdoor furniture products.
Plastid
A plastid is a self-reproducing organelle of plants and algae. A plastome is the DNA genome of a plastid. They are like tiny machines inside cells: each makes or stores important chemicals used by the plant.
Examples of plastids are:
Plastids in algae and hornworts may differ from plant plastids. In algae, the term "leucoplast" is used for all unpigmented plastids and their function differs from the leucoplasts of plants.
Glaucocystophytic algae contain muroplasts, which are similar to chloroplasts except that they have a cell wall, similar to that of prokaryotes. Rhodophytic algae contain rhodoplasts, which are red chloroplasts which allow the algae to photosynthesise to a depth of up to 268 metres.
Plastids are one of the many different types of organelles in the cell. In endosymbiont theory, plastids originated as cyanobacteria. This was first suggested by Mereschkowsky in 1905. Schimper in 1883 had said chloroplasts closely resembled cyanobacteria.
Almost all chloroplasts are thought to derive directly or indirectly from a single endosymbiotic event. Mitochondria also derive from symbiosis, but chloroplasts are found only in plants and protista. The chloroplast is surrounded by a double-layered composite membrane with an intermembrane space; further, it has reticulations, or many infoldings, filling the inner spaces. The chloroplast has its own DNA, which codes for redox proteins involved in electron transport in photosynthesis.
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