University of Nebraska Medical Center

Reported Cases of West Nile Virus Up from Previous Years

source: dnrec.delaware.gov

Public Health in the National News – Mosquitoes are more than just a nuisance. They are a real public health hazard, carrying a number of infectious diseases, most notably in the United States West Nile disease.

Already this year, 1,118 human cases of West Nile virus (WNV) have been reported in the United States, more than has been reported for a number of years. The outbreak has affected 37 states thus far in 2012, with Texas reporting the most number of cases. In Nebraska, recent weeks have seen a sharp increase in cases.

West Nile is an African disease that first appeared in the United States in 1999 and rapidly spread across the country. Its reservoir is various animals, especially birds, and it spreads to humans via mosquito bites. Most cases occur in the late summer months. In addition, the virus may be spread through blood transfusions or transplants.

Individuals with the most risk of WNV infection include those having weakened immune systems (i.e., HIV), the older or the very young, and those who are pregnant. The incubation period lasts five to fifteen days from the initial bite. The disease is diagnosed by antibody tests on blood and/or spinal fluid.

Most West Nile cases have no symptoms at all. The more mild form of the disease, West Nile fever, may show symptoms including fever, headache, or vomiting, while the more severe forms (encephalitis and meningitis) can show signs of confusion, loss of consciousness, muscle or arm/leg weakness, or stiff neck. Paralysis has been reported. Although rare, the more severe forms can potentially lead to death (about 10% of individuals with brain inflammation). However, in almost all mild cases, the outcome is good. Neurologic complications are much more common in the elderly (see Figure 1 below). West Nile symptoms are similar to many other diseases, so the usual directives about when to contact your physician apply, namely with a very high or prolonged (e.g., more than several days) fever, or neurologic symptoms such as confusion, stiff neck, weakness of an extremity, or unusually severe headaches.

There is no treatment for West Nile infection, so the focus is on prevention. To prevent infection individuals should avoid mosquito bites when possible, however, if you are going to be in an area with mosquitos, use mosquito repellant, wear long sleeves and pants, and avoid areas where standing water is present. Insect repellants with DEET can be effective for three to eight hours depending on the amount of DEET in the product. Higher DEET concentrations (e.g., above 30%) provide longer protection.

Source: MMWR 60:1013, Aug 5, 2011.







This article was written by Philip W. Smith, MD, professor, UNMC Internal Medicine, Division of Infectious Diseases, and UNMC College of Public Health Department of Epidemiology; and Michele Kassmeier, BS, graduate student in the Department of Epidemiology.

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