How the West Nile Virus Works – Working against our Health

The West Nile Virus is something that the United States media never used to bother about much, not that it didn’t exist or anything, it’s just that it existed somewhere else.

The somewhat abstract concept of “elsewhere”, however, which might mean just down the road to some folks or half a world away to others, changed in the summer of 1999 when it was Americans who started to die from its effects.

Viruses do not stop at borders, and sooner or later, with such modern realities as global trade and travel, the West Nile Virus was going to reach North American shores.

Not SLE, but WNV

At first, the outbreak of the serious and potentially fatal neurological disease in New York five years ago known as encephalitis, which is an inflammation of the brain, was blamed on the ailment known as St. Louis encephalitis (SLE), which is relatively common on this continent.

The CDC (Centers for Disease Control and Prevention) knew that it was some sort of arbovirus (an abbreviation for arthropod borne virus) but they didn’t know which one. Soon however, as cases of horses also suffering from encephalitis were linked, as well as flamingos at the Bronx Zoo, and reports of dead wild birds like crows and others starting a few months previously, the scientists realized that it was a newcomer that was jointly responsible for all of these situations.

And that newcomer was soon recognized as being the West Nile Virus.

Meet the family

WNV is one of a group of viruses known as a “complex”. Within the family known as Flaviviridae; the genus Flavivirus exists - this is the antigenic complex with Japanese encephalitis being the `chief’ virus amongst them, and WNV and SLE and others making up more of its number.

In science talk, these Flaviviruses are all around 40-60 nanometers in size (one nanometer being one billionth of a meter) and are single stranded and enveloped RNA viruses with icosahedra symmetrical nucleocapsid, and somewhere between 10,000 to 11,000 bases!

In layman’s terms all this means is that viruses are small, complicated and nasty.

Searching for a new home

Of course this point of view is from our perspective. Viruses might say that they are misunderstood; after all, don’t such ancient forms of life deserve respect?

Well no, not really. It’s true that viruses like WNV have no choice in the matter, they are after all merely looking to reproduce themselves like all life forms do, to perpetuate their lineage - and all that.

But why do they have do it inside us, or our animal friends?

A matter of multiplication

Viruses need us or some kind of host body to survive. Most viruses can’t survive for long outside of another living being, and so they have to infect - reproduce - infect - reproduce ad infinitum in order to live.

The trouble is, that they can cause all sorts of diseases and of course death in the unlucky host, while this behaviour is going on.

The ironic thing is that the West Nile Virus doesn’t even manage to multiply itself that well in humans (we are what’s called a dead-end host) so you’d think it would just move on, or give up or something - out of decency.

The percentage equation

To be fair, in truth most people infected with WNV don’t actually suffer any symptoms at all. Although they may develop antibodies in their system (which are the body’s defensive measures against the antigens of the virus) these showing up in tests are the only way some might ever know they had ever been on the WNV hit list.

But some will not be so lucky.

Around 20% of people infected will be struck down with West Nile fever (WNF). Though this should not last too long, it nonetheless isn’t too pleasant; with fever, headaches, general tiredness and malaise and aching muscles all over etc, amongst it delights. Oh, and a skin rash can also sometimes arrive on the scene as well - just to cheer the patient up a bit.

The unlucky few

This might be bad enough, but for somewhat less than 1%, it will be a whole lot worse.

No joking here, for if West Nile Virus infection triggers the onset of severe diseases, with what are known as neuroinvasive diseases like the aforementioned West Nile encephalitis or meningitis (which is an inflammation of the membranes that line the brain and the spinal cord); then the patients’ life is threatened, particularly so in the case of older and elderly people.

Symptoms of severe infections include weak muscles, a high fever, a very stiff neck, extreme headaches, bodily trembling, a dazed and disorientated state of mind, convulsions, coma and paralysis.

Don’t dismiss your health concerns lightly

So if you or a friend or relative starts to exhibit any of these serious symptoms, contact a local healthcare provider straight away.

The individual concerned, will give a blood sample if the physician sees the symptoms are indeed serious, especially so if they have travelled to or live in any region which has been involved in an outbreak of WNV.

Diagnosis can be suspected based on clinical observation of symptoms, and the proper help offered. Though there is no actual treatment for the West Nile Virus itself at this time, IV fluids and respiratory assistance can be given if the patient needs hospitalization, as well as having secondary infections properly guarded against. Many people do recover from West Nile encephalitis (although even so, the affects can be long lasting in some instances).

The blood sample will be sent off to a public health (or commercial) laboratory where it will be tested for purposes of confirming the initial diagnosis.

This most commonly involves a search for antibodies that the infected person’s body will start to produce in response to the disease agents. These harbingers are known as IgM antibodies, and can be found in blood and what is known as cerebrospinal fluid (CSF). This is the fluid that surrounds the spinal cord and brain.

The test may not be positive at first, but will be shortly after (around a week) if WNV infection is indeed the problem.

The stats

Sometimes these tests are not enough to convince the researchers that WNV is the cause, because of indefinite results. So more detailed works are required before notifying the CDC, and the officially reporting of a new case in the government compiled statistics.

This is why the statistical count can sometimes appear to be out of step with local findings. The supplementary tests (which are called plaque reduction neutralization tests or PRNT) will take a while longer, because they involve the growth, or culture as it is known, of the virus in a laboratory.

Once successfully incubated, they are further sealed and then dehydrated, before being placed into a resin and sectioned up. After having special chemicals added, the sections or `grids’ are duly inspected under a powerful electron microscope, which can show specimens in incredible magnification as it utilizes electrons (obviously) rather than visible light as does a regular microscope.

All this delay, or the possibility of what is known as a `false positive’ in initial testing, will not affect the type of treatment. Obviously if a person is ill with serious symptoms, then they need to be treated. But it is important to the long term war against WNV that the statistics are correct; which is why some state public health labs repeat tests carried out in private laboratories, or hand the samples over for the CDC to do their own tests on, before the instance is officially recognized as WNV.

This helps to map out the spread of the virus, as well as confirming that no other virus or disease is present.

Bloodsuckers

Of course such incubation of the West Nile Virus is under laboratory conditions, but the problem with viruses is that they tend to have their own plans of incubating. As well as this they need to spread, and in the case of arboviruses that is where our old friend the mosquito comes in.

These arthropod borne viruses are present in the natural world and kept on the go by transmission between various receptive hosts. Mosquitoes and their brethren; ticks, sand flies, ceratopogonids (known as “no-see-ums” in North America, or `midges‘ in some other countries) are responsible for transmitting viruses around through their blood meals.

In the United States and Canada the culex species of mosquito is the primary bridge vector (transmitter) that does this, which is why the outbreaks in humans occur at peak mosquito breeding months.

The cycle is known as a zoonotic one, as it involves non-human primary hosts (birds in the case of the WNV). The virus is carried in the salivary glands of female mosquitoes and can infect birds that they bite. These birds, if of susceptible species, will be viremic (have the infectious virus circulating in their blood stream) for up to four days. However, birds can become immune to the virus for the rest of their lives if they do not themselves develop encephalitis and die (it is thought that most birds will survive the virus), so a lot of mosquitoes need to bite a host whilst infectious to further the spread of WNV.

Most of them may die before biting anything else, which would be good news. But other birds or animals like horses, (or people, we’re animals too) may get targeted by an infectious mosquito looking for its supper.

This is not really in the viruses interests, because horses and humans are usually `incidental’ hosts (same as dead-end hosts, but sounds more scientific), which though capable of suffering mild or serious illness due to the virus, do not very often develop highly infectious viremias in their blood, and therefore will not help the virus much by enabling it to be further transmitted.

Remember that the portion of blood a single mosquito sucks up is truly tiny, so if the virus cannot reproduce itself properly in a host then it is highly unlikely to get passed on through the actions of only a couple of mosquito vectors.

A calendar event

All this helps to explain why some seasons have the most WNV outbreaks in temperate regions (in the tropics there are always mosquitoes around).

The virus will start up in springtime, when either adult mosquitoes who were infected the previous year and been dormant through the colder weather start to become active or because migratory birds arrive with the virus inside them.

Two things can now happen - the uninfected mosquitoes can bite the infected birds - or the infected mosquitoes can bite the uninfected birds. Either way, it’s all the WNV needs to start off the cycle again.

Transmission will increase through late spring and early summer, and the virus gradually becomes more widespread as the mosquitoes continue to bite on the birds.

So far, West Nile Virus can likely only infect birds and mosquitoes, because these earlier insects generally do not feed on mammals. But when midsummer arrives, other mosquito species like culex begin to peak, and these certainly do include mammals, like humans and horses for example, on their menu list. So now through the rest of summer and early fall, we are at our greatest risk from West Nile Virus.

This is not the whole situation though, for the virus can also be transmitted onwards through what is known as vertical transmission. This is where the eggs of an infected female mosquito can receive the virus during their formation, so when they hatch out later, they too can be the cause of infection if they live long enough to bite.

To spray or not to spray? That is the question

A lot of the time the answer will be yes. Mosquitoes do not receive much sympathy; although some people regard insecticides and pesticides in general as being a far greater threat than WNV, the public health authorities will not take chances that the virus could have been stopped, but wasn’t, thanks to their lack of action.

Of course this costs money, and funding will have to be found, and a detailed risk assessment carried out before permission is given.

Adulticides can be very effective at dramatically cutting the number of mosquitoes flying about looking for a meal, as well as the use of special bacteria to kill larva in water, or oils to spread across the water surface and prevent the larvae from using their breathing tubes.

But some will always survive, so citizens can help as well; not least by the use of chemical repellents and the fixing of door and window screens, or by making sure possible mosquito breeding sites in their neighborhood are kept to a minimum.

Remembering that mosquitoes are more active at dusk and dawn will be of use as well, so adjust behavior accordingly if your state, city, town or county has an outbreak of WNV.

The government is on the case

The CDC and other arms like the FDA and the USDA are very active in the fight against WNV, with help given to affected states for improved mosquito prevention and control measures; as well as the effective coordinating of local efforts and helping with information sharing.

They are also doing other work like developing new testing procedures and seeing that efforts to find a cure for West Nile encephalitis in humans are ongoing.

But it may be a long fight to win, mosquitoes can develop resistance to chemicals, and the virus probably has a few tricks up its sleeve yet.

WNV only arrived in North America five years back, but it probably won’t want to leave again.

About The Author

Matt Jacks is a successful freelance writer providing advice for consumers purchasing mosquito repellents and various mosquito control products and tips on recognizing symptoms of the West Nile Virus. His numerous articles offer tips and valuable tips and insight on a wide range of topics.

This article on "How the West Nile Virus Works" reprinted with permission.

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