Marcy Broden
Psychology
Introduction:
In the past six years I have had a lot of hands on experience with West Nile Virus.I found myself in the summer of 1999 working for my county's Environmental Special Project's department and I had no idea what I was in for with this job. West Nile Virus became a concern in the summer of 2000 in my area and I was able to learn almost every piece of information about it. I was involved in the surveillance project created to avert the spread of West Nile Virus and also to monitor it. Although I had no prior experience in anything environmental I found myself becoming more and more interested in it. The reason why I chose to do this web page on West Nile Virus was to be able to use the information I've gained to pass it on to others. The purpose of this page to explore the origin, symptoms, and transmission of the virus. I will also be going into some detail about different types of mosquitoes and some of the things that I did working for the surveillance program.
What is West Nile Virus?
West Nile virus is a mosquito-borne RNA flavivirus.The flavivirus group contains viruses that spread by insects and cause disease in humans and animals. In 1937 it was first identified in an adult woman in the West Nile district of Uganda. The virus became known as a severe cause of encephalitis in elderly adults in during an outbreak in 1957 in Israel. In the early 1960's it was first discovered in horses in France and Egypt (1).
West Nile virus was mainly seen in Africa, Asia, Europe and Australia. Human outbreaks existed in the 1990's in Europe and in the Mediterranean area, with the largest outbreaks in Russia, Israel and Romania. The viral strain that was introduced in the United States in 1999 likely originated from a West Nile virus homologue that was in Israel during 1998. The virus was first recognized in 1999 in New York City when it caused illness in 59 people. In 2000 and 2001 West Nile virus spread rapidly in the South and Midwest, establishing enzootic activity. Enzootic activity is when there is evidence of a virus in mosquitoes, animals or humans. There was enzootic activity in these years in 28 different states although large numbers of human infections were not yet a concern. In 2002 West Nile virus spread westward and activity was reported in all but 6 states. The virus caused the largest human encephalitis epidemic in U.S. history. Between June 10th and December 31st 2002, there were 4,156 cases of West Nile infection which included 282 deaths. The epidemic of 2002 was concentrated in the Ohio and Mississippi river valleys. The geographic region of this epidemic was similar to an epidemic in St. Louis in 1975. In the southern states human cases of the virus occurred from the summer months through December of 2002. In northern states the epidemic started later in the summer and ended earlier in the fall mainly because of cooler temperatures. In 2003 there were 4156 human cases which included 284 deaths (1).
How do you acquire the virus?
The main way to acquire West Nile virus is by being bitten by an infected mosquito. Mosquitoes acquire the virus when they feed on infected birds which may circulate the virus in their blood for a few days. Very few mosquitoes are infected with the virus and less than 1% of people who get bitten and become infected will become severely ill. The virus eventually goes to the mosquito's salivary glands. During later blood meals the virus may be injected into humans and animals where it can multiply and cause illness. . The culex mosquito species is the main species of mosquito that carries West Nile virus. In temperate areas adult mosquitoes arise in the spring and infect birds which continues until fall. Infected mosquitoes may also overwinter in culverts and catch basins. Year round transmission of the virus is possibly in tropical regions. Overwintering means it is possible for mosquitoes to remain alive through the winter. The bites of culex mosquitoes are painful and these species are persistent. They tend to search for blood meals at dusk and after dark. They will readily enter dwellings for blood meals. Aedes and ochlerotatus search for a blood meal early in the morning , at dusk and into the evening. They usually do not enter dwellings. Some can be daytime biters especially on a cloudy day or in the shade. Mosquitoes feed primarily on nectar and only female mosquitoes require a blood meal. The blood meal is necessary for egg production in females resulting from the protein in the blood. (2).
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The picture on the left is the culex pipien species. The picture on the right is of the aedes species. Mosquitoes differ physically by patterns on their wings, markings on their bodies and in their sizes. Females have parts to pierce the skin which males do not because males do not take a blood meal. (7). |
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Different species of mosquitoes develop in different types of areas. Females lay eggs in stagnant water. The eggs hatch into larvae which then grow into pupae. The pupa stage is the last stage before the mosquito becomes an adult. Some of the main areas where mosquitoes breed are in catch basins found along roads. Clogged rain gutters, bird baths, flower pots and anything else that can hold water are also possibilities for mosquito breeding grounds. Excavated areas where large holes are left behind that hold water are a threat. Tire piles are a large source for mosquito breeding as well. There are so many areas where mosquitoes can breed and there will never be a way to simply eradicate all of the breeding areas.
West Nile virus has also been found to be transmitted through blood transfusions. In 2002, the first case of someone acquiring the virus through a blood transfusion was seen. In June 2003 blood collection agencies implemented investigational West Nile virus nucleic-acid tests to screen all blood donations from the blood supply. The screening was performed on approximately six million units during June through December 2003, which resulted in the removal of at least 818 blood donations from the supply. During 2003, there were a total of 23 suspected cases of the virus being transmitted through blood transfusions. Public health authorities reported 15 suspected cases among patients who had the virus after receiving transfusions. Out of the 23 investigations, six were confirmed, 11 were noncases and three were inconconclusive. As of March 27, 2004, three cases remained under investigation (5).
In 2002, there was once case of transplacental (mother-to-child) transmission of the virus reported to the CDC. In this specific case the infant was born West Nile virus infection and severe medical problems. Still it is unclear if the virus caused these problems or whether they were due to other causes. After the report of this case the CDC and other state and local health departments formed a registry to keep track of the birth outcomes among women who had the virus during pregnancy. Three other pregnancies in which the mother became infected with the virus were detected and evaluated in 2002. In all three of these cases none resulted in the fetus acquiring the virus.
In 2002 there was a case in Michigan where it appeared that the virus was transmitted through breast milk. A new mother in Michigan had contracted the virus from a blood transfusion shortly after giving birth. After some analysis was done, there was evidence of the virus in her breast milk. Three weeks later the baby's blood tested positive for the virus. The baby had minimal outdoor exposure, so it was unlikely that the virus was acquired through a mosquito. Presently the child is healthy and has no signs of the virus. (2).
Risks, Symptoms and Treatment
West Nile virus is equally distributed among all age groups and in both sexes. However, the occurrence of encephalitis and death increases among person 50 years and older. Also people with compromised immune systems are more at risk. During the 2002 epidemic, 9% of patients with meningitis or encephalitis died. In more recent urban epidemics, failure to use mosquito repellant, living in a building with a flooded basement, and presence of mosquitoes in the home were all factors. Physiological factors do not appear to be risk factors. In December 2002, the U.S. Food and Drug Administration recommended the voluntary withdrawl of blood and blood products that might carry the virus.
Most people who acquire the virus have no symptoms. Approximately one in five infected people develop a mild illness, and one in 150 infected people manifest neurological symptoms. Symptomatic illness generally follows an incubation period of about two to 15 days. The majority of asymptomatic patients have a self-limited illness which may include headache, nausea and vomiting. Chills and fatigue are also common complaints. The acute illness usually lasts less than seven days but fatigue may persist for several weeks. Also patients can develop a rash often on the arms and legs. Approximately 5% of patients with symptomatic West Nile virus develop more severe neurological illness including meningitis, and encephalitis. Patients with West Nile encephalitis have altered mental states and may even experience coma. Patients who have the virus affect the nervous system may experience tremors, and signs of parkinsonism (6).
Physicians should consider West Nile virus in weaker patients who have unexplained neurological problems, muscle weakness, rash or headache during late spring until early fall. The best laboratory test for diagnosing the virus is an IgM antibody test which collects blooms serum or cerebrospinal fluid eight to 21 days after the onset of symptoms. This test is available commercially and through local or state health departments. State public health labs cab usually perform the test within 24 to 36 hours of submission. Since IgM antibody usually does not cross an in tact blood-brain barrier, a single West Nile virus specific IgM positive antibody in CSF can confirm central nervous system infection.
Treatment for West Nile virus is limited. Patients who become dehydrated due to vomiting may receive oral or intravenous fluids. Patients with encephalitis or meningitis may need pain control for headache. There is no cure for West Nile virus and the only things that can really be done is to treat the symptoms that result from the virus. No vaccine is licensed for the prevention of the virus in humans although there is development currently underway (6).
What Can You Do?
Although most people will not be involved with large scale surveillance programs for West Nile virus there are many ways to contribute to minimalizing the spread of the virus through mosquito breeding. Here is a list of things that you can do to keep yourself protected:
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*A product containing 23.8% DEET provides an average of 5 hours of protection from mosquito bites
*A product containing 20% DEET provides almost 4 hours of protection
*A product containing 6.65% DEET provides almost 2 hours of protection
*A product containing 4.75% DEET and 2% soybean oil are both able to provide about 1 and a half hours of protection
West Nile Virus and Animals
Horses are susceptible to West Nile Virus. More horses with the virus recover than die, still there are horses who have died because of it in the United States. Horses become infected with the virus the same way that humans do, through a mosquito bite. The virus is injected into the bloodstream, multiplies and causes illness. Severe illness is caused but the virus crossing the blood-brain barrier and infecting the brain. The virus interferes with normal central nervous system functions and causes inflammation of the brain. People cannot contract the virus through handling or even being bitten by an infected horse. There is a vaccination approved for horses to prevent West Nile virus. There is no reason for a horse to be destroyed if it contracts the virus. Standard veterinarian treatment should be made available and most horses do recover.
West Nile Virus has been identified in more than 200 species of birds. Most of the dead birds were identified as having the virus because of reporting done by the public to the health departments. Birds also become infected the same way through mosquito bites. Their serve as a host for infected mosquitoes. Crows and blue jays are the birds primarily focused for the collections of dead birds. If someone sees a dead bird that doesn't appear to have any external injuries, the local health department can be contacted to see if the bird is eligible for collection. Most health departments only collect certain species of birds and certain times of the year. Also a bird cannot be collected if it has been dead for more than 48 hours and has already started to decompose.
There has been a small amount of infected dogs and cats with the virus. They also contract the virus through an infected mosquito. There is no vaccination available for either dogs or cats and a veterinarian should be consulted to see what kind of repellant can be used. Repellants containing DEET is only approved for humans and should not be used on pets.
West Nile Virus Surveillance
Although most people will not be involved in a large scale West Nile virus surveillance program, I have had the opportunity to work with it for the past few years. In this section I am going to give a brief description of the types of methods that were used to treat infested mosquito areas and traps that were used to collect them. These traps aren't just used by the areas I worked they are standard types of traps and procedure that are used.
Over the past few years I have been exposed to three main types of mosquito traps; light traps, dry ice traps and gravid traps. All of these traps are used to collect adult mosquito samples. A basic light trap consists of a carbon dioxide tank, a net with a small light and a fan, and a battery. The net is hung from a low tree branch so that is about three or four feet above the ground. A battery is attached to power the small light and fan. The carbon dioxide is released by the net and the fan distributes the carbon dioxide around it. Mosquitoes are attracted to carbon dioxide which is why they also can be found hovering around the mouth when one exhales. The mosquitoes are attracted to the light and made lethargic by the carbon dioxide. The enter the net and remain there until they are collected the next morning. These traps are set at dusk and usually picked up between 12-14 hours later. I used these traps mainly in the beginning of my work with the program but we gradually used more efficient traps as time passed.
Dry ice traps are similar to light traps in the way that they function. A dry ice trap consists of what looks like a beverage cooler, a battery, dry ice and a net. The trap is also hung from a tree with the dry ice placed in the cooler. The battery powers the light but its the disintegration of the dry ice that allows for the release of carbon dioxide to trap the mosquitoes. This type of trap is safer because there have been reports of carbon dioxide tanks exploding. Mosquito counts also tend to be higher in traps because there are fewer malfunction since there are no tanks. Using the tanks was always a challenge because they had to be gaged accurately and speed and amount of carbon dioxide needed to be the right amount. Too much or too little wasn't sufficient.
Gravid traps are also used numerously. The consist of what looks like a plastic bucket or a toolbox, a net, a battery and a mixture of really disgusting water. The net rests on top of the main part of the trap. The battery powers the fan and the light which attracts the mosquitoes into the trap. Water containing dried leaves, grass and usually yeast (we actually used beer sometimes) is added into the trap. This water mixture provided a perfect breeding environment for mosquitoes. Adults will go in there to lay eggs and become trapped and end up in the net. These traps are also set at or a little before dusk and are picked up the next morning.
When the nets are picked up the morning it's important to make sure they are tied properly. It's not too fun to have mosquitoes flying around your car when you're driving to work! The nets are usually thrown into a large cooler filled with the dry ice to kill and preserve the. After about 10-15 minutes the nets are removed and the mosquitoes are counted and placed into labeled bottles to be shipped out to be tested.
Another aspect of my job was to assist in larviciding and adulticiding. Mainly for larviciding the catch basins on the roads were the focused. A chemical which is a bacteria was used to drop into the grates in the road. The bacteria is actually placed on birdseed and this allows for the bacteria to remain in tact until it needs to be dispersed into the water. The chemical kills mosquito larvae so they never have the chance to grow into adults. It's a tedious job treating all of those drains, that's all I have to say!
Larviciding also included some manual labor which I was lucky enough not to have to by myself. In large areas of standing water the same chemical was placed into a machine which is strapped onto one's back. The machine is powered so it allows for the chemical to be dispersed in larger areas and in further distances. The chemical is similar as to what is used in the catch basins and is released into the water in its granule form. This works well in areas that aren't able to be reached by foot. The purpose of this is also to mosquito larvae to prevent them from growing into adults. Altocid tablets are also used to kill mosquito larvae. Tablets resemble charcoal briquettes and are also used to treat large areas of standing water.
Adulticiding is used in extremely infested areas with adult mosquitoes. It's the same process and involves a slightly different chemical which is mixed with water to produce a fine mist. The mist is sprayed into the air to kill the adult mosquitoes.
Conclusion:
For most people there is no cause for alarm when it comes to West Nile virus. Most people who contract it won't even show any symptoms and even mistake it for something else. The elderly and people with compromised immune systems are at the most risk. Media at times presented information about West Nile virus misleadingly and caused people to be more afraid then they really should be. There will always be mosquitoes around and inevitably everyone will be bit on more than one occasion, but the chances of contracting the virus are slim. Repellent is key in infested areas and mosquito breeding grounds can be eliminated by simply removing some water. West Nile virus has not been here very long but it is not going to be disappearing anytime soon but that's not reason to be afraid to go outside and do normal activities. Precautions should be taken but living life shouldn't be compromised.
Bibliography
1. Center for Disease Control (2004). Questions and answers: Cases of West Nile human disease. <http://www.cdc.gov/ncidod/dvbid/westnile/qa/cases.htm>(2004, October 20).
2. Center for Disease Control (2003). Questions and answers: Transmission. <http://www.cdc/gov/ncidod/dvbid/westnile/qa/transmission.htm> (2004, October 20).
3. Center for Disease Control (2004). Questions and answers: West Nile virus, pregnancy and breast feeding. <http://www.cdc.gov/ncidod/dvbid/westnile/qa/breastfeeding.htm> (2004, October 20).
4. Center for Disease Control (2004). Questions and answers: West Nile virus vaccine. <http://www.cdc.gov/ncidod/dvbid/westnile/qa/wnv_vaccine.htm> (2004, October 20).
5. Center for Disease Control (2004). Update: West Nile virus screening of blood donations and transfusion-associated-transmission-United States-2003. http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5313a1.htm> (2004, October 20).
6. Huhn, G.D., Sejvar, J.J., Montgomery, S.P. & Dworkin, M.S. (2003). West Nile virus in the United States: An update on an emerging infectious disease. American Family Physician, 68, 4.
7. (2003). Mosquitoes and West Nile virus. <http://www.ourbeehive.com/mosquitoes.html>
8. (2004). West Nile virus. <http://www.encyclopedia.thefreedictionary.com/West%20Nile%20virus>.
*I also was able to use a lot of the information that I've learned in the past 6 years for this web page. I can thank the Environmental Special Projects Department of Luzerne County Pa. for that!*