West Nile Viral Infections
West Nile viral infections are caused by a flavivirus with the unusual ability to affect vastly different animal species: birds, horses, and humans. While far more deadly to birds than their larger counterparts, West Nile illnesses can have significant impact on mortality and morbidity among humans. First identified nearly seventy years ago in Uganda, West Nile virus has spread through Africa, Asia, the Middle East, and the United States, bringing with it a variety of symptoms ranging from undetectable to fatal.
Mimicking a number of other known ailments, the disease has proven a challenge for the medical community to identify and treat. Meanwhile, West Nile viral infections have grown alarmingly in number, with an estimated five percent of the population possibly infected (Beeman A6).
Transmission
In the vast majority of cases, West Nile infections are vectored to humans via mosquitoes who have bitten an infected bird. However, this blood-borne pathogen has also reportedly been transmitted through blood transfusions and organ donations, as well as isolated cases of transmission across the placental barrier or via breast milk (CDC).
Geography
Although West Nile Virus was first reported in Uganda as long ago as 1937, it wasn’t until 1999 that it was identified in the United States. This was initially discovered when a number of dead birds in New York were found to be infected (Girard 297). Once in the states the virus began spreading rapidly. According to Girard, in 2003 nearly ten thousand cases had been reported (298). While nearly every state has been affected, the vast majority of infections have occurred in Colorado, California, and Arizona (CDC; Beeman A6). Beeman reports, “About five percent of the population is believed to have become infected”(A6).
Risk Factors
While anyone can acquire a West Nile viral infection, those highest at risk are individuals who spend time out of doors in areas where mosquitoes congregate, such as near standing water. The risk of West Nile is greatest between summer and fall, presumably linked to the proliferation of mosquitoes during that period (CDC).
Blood transfusion recipients and breast-fed infants pose a slight risk, though blood banks have begun routinely screening donor blood for the virus and few cases have actually been traced to transfusion or breast feeding (Beeman A7; CDC).
Those most at risk for becoming seriously ill from a West Nile infection are the elderly (individuals more than fifty years of age) and/or who have significant co-morbidities such as Chronic Obstructive Pulmonary Disease (CDC).
Symptoms
Symptoms range in type and intensity based on the severity of infection, and can last between three days and several months. Eighty percent of infected individuals remain asymptomatic and are can be unaware of having been infected (Beeman A6). In those who will become symptomatic (generally three to fourteen days after exposure), they will experience flu-like symptoms such as fever, head and body aches, fatigue, nausea and vomiting, and possibly a slight rash. These symptoms will resolve on their own, generally within a few days. (CDC)
A small number, approximately one in every 150 cases according to Beeman, will progress to serious symptoms such as high fever, severe headache, stiff neck, coma, convulsions, disorientation, visual disturbance, numbness, or paralysis (A6). The elderly and those with chronic illness are particularly susceptible to severe manifestations of West Nile Virus. Serious cases tend to last quite a bit longer, often several weeks, and can become life threatening if not managed in an acute care setting. In addition, if paralysis is present, the effects may become permanent (Girard 298).
Recently, it has been recognized that there are actually two different manifestations of West Nile Virus: West Nile viral infection and West Nile fever, a less severe infection. (Watson 360). Symptoms for both are similar with one exception: in West Nile fever, according to Waston, no signs of neurologic problems are seen (361).
Diagnosis
Diagnosing West Nile infection can be difficult for physicians, both because it has become prevalent only in the past few years and also because the symptoms mimic several other better known diseases such as encephalitis, meningitis, and Guillan Barre Syndrome. As cases climb in number and physicians become more aware of the disease (particularly in hot spot areas like the Southwest), it will hopefully become increasingly common to automatically include West Nile Virus titers screening of any patient’s blood who presents with symptoms of flaccid paralysis or encephalitis. This blood test can confirm or rule out a suspected diagnosis of West Nile Virus (Beeman A6).
In addition, West Nile fever can be diagnosed/differentiated from West Nile virus infection by examining the patient for signs of neurologic symptoms. Those without neurologic signs are considered to have the lesser form, West Nile fever (Watson 361). The presence of neurological symptoms indicates West Nile infection. Both forms are clinically significant, though generally West Nile fever does not tend to require as much medical management and the mortality rate is less. However, the fever variant can still cause weeks’ worth of illness and possible hospitalization, so Watson advises that these cases should also be watched carefully (365).
Treatment
As with all known viruses, there is currently no cure for the West Nile virus. Treatment must instead be focused on aggressive management of accompanying symptoms and of any secondary complications.
Mild cases are often subclinical, requiring no supporting treatment before clearing on their own. However, more severe cases require active management, often in an acute care setting, in order to control severity of symptoms such as flaccid paralysis and respiratory distress or failure (CDC). Mechanical ventilation for severe respiratory symptoms or management of paralysis involving the respiratory tract may be necessary as well.
While medical management of symptoms can help reduce mortality rates, West Nile Virus has become a significant cause of illness in the United States, with an increase in numbers each year. More than five hundred deaths have been attributed to the disease in the past two years, spawning a flurry of studies and activity on the part of health officials to help halt the spread of the virus (CDC).
Clinical trials are currently underway to study the treatment potential of using West Nile virus antibodies acquired from previously exposed individuals on currently infected patients (Hampton 916). If successful, this could lead to the development of a vaccine against the disease.
Prevention
With no available vaccine against West Nile Virus at the present, prevention currently depends on avoiding exposure. This is particularly important for high risk groups such as the infirm and elderly. It is recommended that during warm months people remain indoors as much as possible, particularly around dusk and dawn when mosquitoes tend to be most active (Beeman A6; CDC). When necessary to be out of doors, the use of long sleeved garments and pants are advised. Insect repellents containing DEET should be used.
Since mosquitoes breed in standing water, these areas should be eliminated (where possible) or avoided. Wading pools, buckets, bird baths, fountains, and puddles should be drained; avoid lakes, ponds, and pools. Use of mosquito netting around outdoor gazebos, tents, and other exterior use areas can also help minimize contact. All doors and windows should have screens that are intact and in good repair during warm weather months as well.
Any dead birds that are found should be reported to the local health department in order to assist in identifying and tracking potential virus “hot spots” as well as to obtain instructions on proper disposal methods (CDC). Outdoor activity should be especially limited in locations where many such birds have been discovered.
Identifying areas where the virus is concentrated is important so that the application of appropriate vector control techniques can be considered. Spraying high risk zones with pesticides can help decrease the mosquito population (Staff A4). Use of such methods must be employed carefully and weighed against the potential risks of widespread use of such chemicals on public health and the ecology of each particular zone (Staff A4). Still, the judicious use of DEET-based pesticides can be an effective means to controlling the spread of West Nile infection from the larger hotbeds of viral activity.
Conclusion
Despite efforts to control West Nile Virus, the number of cases continues to climb each year. With more than 500 deaths in the United States over the past two years and thousands more hospitalized for medical management, West Nile infections have become a significant illness among humans, particularly the elderly and those living in high risk geographical areas such as the Southwest United States.
Those at risk, and the populace in general, do not have a vaccine at their disposal to help prevent infection. Instead, strict avoidance of mosquitoes, the human vector of West Nile Virus, must be relied upon to prevent exposure to the disease. Taking measures to steer clear of standing water and outdoor activities during the warm weather months can help minimize the chance of coming into contact with an infected mosquito.
For those in the five percent in the world populace believed to have been infected, a fortunate eighty percent will suffer no symptoms. Most who become symptomatic will have only mild flu-like symptoms and will recover spontaneously within a few days. However, for the small minority who develop severe symptoms, medical management, typically in an acute care setting, will be required in order to prevent loss of life due to respiratory failure secondary to paralytic symptoms or other complications. Some will suffer neurological symptoms with possibly permanent affects. Cases with neurologic involvement are the most likely to suffer severe consequences, and are differentiated from patients in whom neurologic complaints are absent. However, the less severe West Nile fever can still cause significant illness.
To combat this increasingly prevalent disease, health officials including the Center for Disease Control (CDC) and Department of Public Health are currently involved in tracking and studying the virus. Hot spots, or geographic areas of high viral concentration, can be identified by reporting all cases of West Nile Virus in humans as well as the discovery of dead birds. Some such areas may require vector control methods such as large scale pesticide spraying, preferably by ground to prevent unwanted ecological and health effects.
As with any serious outbreak of illness, it is only through the mutual efforts and cooperation of the medical community, government organizations, and the population itself that West Nile infections can be stemmed and controlled. By organizing and combining public education, vector control measures, and medical research, West Nile Virus may one day go the way of smallpox and be, for all intents and purposes, eradicated.
