Mosquitoes and West Nile Virus

I have college degrees in Entomology and Environmental Health. I have been an avid collector of insects for 34 years, and deeply enjoy the time I am able to spend working in a local University insect museum. I am absolutely fascinated by insects and other arthropods and am pleased whenever I can pass this enjoyment on to others, such as those who are lucky enough to find our website – BugInfo.com – and the wealth of information we hope to offer on it.

Insects are wonderful things, with respect to their beauty and the reliance all of nature has on insects for the proper flow of natural environments. However, there is a dark side to insects too, and we absolutely MUST understand the ability many of them have to cause us harm. Only by educating ourselves with the facts can we make the proper decisions on how to proceed with avoiding the problems. There are many “urban legends” out there that we read about, and wonder whether or not they are true. If we are swayed to believe things that are not true we may be led to take action by demanding a response that is not warranted.

Mosquitoes and Disease

Of all the insects that are destructive to humans none is worse than the mosquito. Among the various diseases spread by mosquitoes is Malaria, which kills two to three million people each year in the world at this time. Yellow Fever and Dengue are two more devastating mosquito-borne diseases. Yet another disease spread by these critters is Encephalitis, actually a compilation of around 7 or 8 strains of viruses that cause similar effects in infected people. Encephalitis is closely tied to birds, as it is in birds that the encephalitis virus must live for a period of its life cycle, and when mosquitoes then feed on infected birds they acquire the virus, which then can be passed to a person who is bitten.

The United States is not immune to the horrors of mosquitoes and their diseases, and many decades ago these diseases were quite common in this country. It has been through the diligent efforts of Mosquito and Vector Control Agencies and the pest control industry that we have beaten back the disease. We certainly have plenty of the species of mosquitoes that are capable of spreading any of the mosquito-borne diseases, but for the most part the disease agents themselves – the bacteria, viruses, or Plasmodium – have been kept out of the mosquito populations. Encephalitis is the exception, but careful monitoring around populated areas allows the mosquito control agencies to determine when infected mosquitoes are getting “too close”, and they can proceed with intense mosquito control programs.

Now, however, there is a new player in the country, and this disease is called West Nile Virus, also referred to as West Nile Fever. This virus is believed to have originated in Africa, where it likely has existed for millions of years. For many years now it has caused infections and death in people in many African and Middle East countries, and in the past few years has been reported in Europe as well. Until 1999 it had never been reported in the Western Hemisphere (North America and South America), but that year it occurred in New York, causing the death of 7 people in the summer of 1999.

How did West Nile Virus get here?

As with anything new and frightening there already are extraordinary claims emerging about West Nile Virus, including that it is a government conspiracy or that it is a product of bio-terrorism. These kinds of scenarios are at best outrageous, and at their worst are criminal. There simply is no evidence whatsoever of such things, but it makes a lot of people feel better to be able to blame someone. The most reasonable explanation for the sudden emergence of this problem in the United States is the same reason we have so many other imported, exotic pests in this country – the world is getting “smaller”. Human travel takes us everywhere in a very casual style, and the likelihood that we may bring things back in our suitcases or boxes of souvenirs is very high.

About 10 years ago a new mosquito species entered the U.S., called the Asian Tiger Mosquito. While it is not known with absolute certainty, it is believed it hitchhiked here in pools of water in tires that were brought here from Asia for recycling. West Nile Virus most likely came with infected mosquitoes that hitchhiked on airplanes or ships coming from Africa or another country where the disease already existed. Once in the population of people in the United States it was picked up by some of our native mosquito species, and now appears to be a permanent resident of this country.

Where has West Nile Virus been found in the U.S.?

Like other encephalitis-like viruses birds are an integral player in the life of the West Nile Virus. Mosquitoes that are infected with the virus feed on a bird, transferring the virus to the bird. Other mosquitoes that feed on the blood of that bird can then be infected, and so on. To date crows seem to be the most sensitive birds, and many hundreds of them have been killed by the disease. However, up to 20 other kinds of birds have tested positive for the virus, including other migrating birds such as mallards and robins. Several species of hawks as well as the Bald Eagle have tested positive as well.

It is possible that it is within these infected migrating birds that the virus spreads. While initially found in New York City in 1999, the known range of infected birds by October 2000 was as far south as North Carolina and as far north as Maryland and Washington DC. Wherever infected birds fly it is possible for the disease to be spread, and at the time of this article’s creation in summer 2004 all of the contiguous states of the United States are known to have infected birds. The summer of 2004 found the first human cases in California, so West Nile Virus now is here to stay throughout our country.

How is West Nile Virus spread?

It is only by the bite of an infected mosquito that West Nile Virus is passed to people. An infected person cannot spread the disease to another person, and it is unlikely that it can be passed directly from infected birds to people. It must be injected into the blood stream, and this is the mechanism mosquitoes use when they feed. It is recommended, however, that you wear gloves or place your hands within a plastic bag whenever you need to dispose of a dead bird. This is good advice when handling any dead animal, and if there are cuts or other openings on your skin it is always possible that pathogens could find their way in.

Several species of mosquitoes appear capable of spreading West Nile Virus, including some that tend to fly in daylight hours as well as those that are primarily night fliers. These mosquitoes cannot survive the cold months as biting adults, but instead pass through the winter in the egg stage that has been placed in some protected environment by the adults the summer before. Obviously, then, transmission of the disease is only likely during those months when mosquito adults are active.

How dangerous is this disease?

West Nile Virus is considered to be a rather mild strain of encephalitis to humans. While many people have been killed by it, and that is a terrible thing, the vast majority of people who become infected with this virus may feel either no effect at all or very mild symptoms. They may experience a mild headache and fever and then recover completely. While it is possible that anyone might be seriously affected by the disease, those who are at the highest risk are the elderly, the very young, and those with weakened immune systems. There currently is no vaccine for this virus for humans, and treatment of the disease for those severely affected is to treat the symptoms until the disease runs its course. If there is a positive aspect to WNV it is that those who receive a mild infection appear to acquire immunity to the disease from then on. The numbers of cases of the disease in the eastern states, where WNV appeared years earlier, are dramatically lower now than in previous years. The highest numbers of cases are in the states in which WNV is just emerging, and no immunity is present in the residents of those areas.

In 1999, in the New York City area, seven people were killed and 62 were seriously ill from West Nile Virus. In 2000 there was a single death and only 17 confirmed cases of seriously ill people. In other countries in Europe and the Middle East it has been responsible for dozens of deaths in several major outbreaks in the past 3 or 4 years, so the potential for major problems clearly exists. As the disease reached the middle states in the U.S. in 2002 and 2003 there were huge numbers of human cases, and Colorado alone accounted for the majority of these cases.

While deaths to WNV are only a very low percentage of the numbers of people who become infected, this does not mean that those who survive are necessarily back to normal. Remember, that West Nile Virus causes an inflammation of the tissues surrounding the brain, and it commonly causes serious and lasting repercussions as it damages brain function. It is very important not to trivialize this disease simply because it does not kill vast numbers of people.

West Nile Virus is also a serious disease of horses, and many thousands of these valued companions died in the first few years that WNV hit the United States. There now is an effective vaccine for horses, and it appears to very successfully stave off the problems in horses.

What should I do to avoid becoming infected?

As with any other “vector” borne disease, the best defense is to keep from being bitten if at all possible. Keeping mosquitoes out of the house by maintaining screened windows and doors is very important. Avoiding outdoor activities in the early evenings, if possible, also will help you to avoid the times of high mosquito activity. Since keeping kids indoors on summer evenings is next to impossible, they should wear long-sleeved shirts and pants if at all possible, and any exposed skin should be coated with mosquito repellent. Repellents with an active ingredient called DEET have been shown to be the most effective. Several studies have been conducted by universities researchers, and the consistent conclusion is that DEET products are capable of providing several hours of protection, while many of the “home remedy” repellents may be effective for only a few minutes. DEET can be used safely and provides the best protection.

You also should take a critical look around your own property, and determine what sites you are allowing that could breed mosquitoes. Since mosquito larvae need to live in water you should empty any containers that do not need to have water in them:

  • Cans, buckets, yard decorations, dog water buckets, barrels, garbage cans
  • Discarded tires!! – these are a huge source of mosquitoes, since they are so hard to empty. If they cannot be removed from the property and recycled properly, then try to drill holes in them to allow the water to drain out.
  • Clogged roof gutters, potted plant containers, etc.
  • “Tree Holes” – some of the most common sources of mosquito larvae, and thus adults, is holes in trees where a branch broke off or trunks come together. These holes need to be emptied of water, filled with sand, or drained by drilling a hole from below.

If you have ponds or other permanent water bodies on your property you can call the local Mosquito Control Agency and see if they can provide mosquito fish for your pond, or treat the water with a biological material that will kill the mosquito larvae. This agency is variously referred to as the Mosquito and Vector Control District, Mosquito Abatement District, or simply Mosquito Control Agency. Your local County Health Department also may have “vector” specialists in their Environmental Health office.

West Nile Virus is a problem, and not one to take lightly. It rapidly is spreading its area of concern as birds spread their territories, carrying the virus with them. However, compared with many other risks in our lives the risk from severe problems from this virus is small. Understanding the disease and its biology and ecology can be important in helping to prevent your risk from it.

One of the important protections you have available is the Professional Pest Control Industry in your area. These are licensed, educated individuals who have access to equipment and materials that may be applied to reduce mosquito populations on your property. A call to them also could provide you with an experienced person who can inspect your property to offer suggestions on steps you can take to reduce the possibility of raising mosquitoes on your own property. West Nile Virus is an important problem, and these technicians are likely to have had some training on the topic at their professional meetings and conferences.

For some very thorough internet sites that cover virtually every aspect of West Nile Virus you might click on the following Internet address:

This is the Centers for Disease Control website, and this agency will offer the most up-to-date information available, and present it to you in a manner that will be factual and trustworthy. It is important to understand a problem in order to be able to avoid it.

Resource: BugBattalion.com/ND