West Nile Virus Skin RashesCraig Kraffert, MD
West Nile Virus (WNV) arrived in North America via New York City in 1999. During that year, 62 cases of WNV were reported. The peak of reported WNV cases occurred in 2002 when almost 3,000 North American cases were officially reported and almost 300 Americans died from the disease.
As of September 11, 2012, all 48 continental United States have reported West Nile virus infections in people, birds, or mosquitoes (Nevada has not had any human cases). A total of 2,636 cases of West Nile virus disease in people, including 118 deaths, have been reported to CDC this year. Of these, roughly half were classified as neuro-invasive disease (such as meningitis or encephalitis) and the other half was classified as non-neuro-invasive disease.
Affected Geographical Areas
The 2,636 cases reported thus far in 2012 is the highest number of West Nile virus disease cases reported to CDC through the second week in September since 2003. Two-thirds of the cases have been reported from six states (Texas, Louisiana, South Dakota, Mississippi, Michigan, and Oklahoma) and 40 percent of all cases have been reported from Texas.
Transmission of WNV
Birds are the WNV’s natural reservoir. Transmission to humans occurs mainly via mosquitoes, but also through blood transfusions and, possibly, breastfeeding if the mother is already infected with WNV. The risk of contracting WNV from blood transfusions has been greatly reduced by new WNV screening of all donated blood and organs. In North America, infections are mainly seen between late spring and early fall when mosquitoes actively feed.
Diagnosis and Symptoms of WNV
Diagnosis of WNV infection is difficult as symptoms are variable and nonspecific but can be accurately detected by a blood test. Recent studies suggest that less than 1% of WNV result in severe/life-threatening neurological disease.
Of those exposed to WNV, 80% have no symptoms. Rashes are reported in approximately 20% (12% to 50% in various studies) of WNV infections and may offer an important clue to those taking care of ill persons with fever of unknown cause. The rash of WNV typically follows the onset of fever by three to five days and disappears when the fever breaks. The rash of WNV is similar to many other viral rashes in that it can be nonspecific in nature. WNV rash typically consists of small pink spots – some raised and some flat – symmetrically distributed on the arms, legs, and trunk. It has been described as looking very much like roseola or measles. One unique feature of West Nile Virus skin rash is that it often superficially resembles folliculitis – or inflamed follicles – even though the bumps are not typically centered around hair follicles.
Public domain photos showing four patients with West Nile virus fever and pink to red, flat and raised rashes on the back (top left), ﬂank (top right), posterior thigh (bottom left), and back (bottom right). Note the resemblance to folliculitis.
Treatment of West Nile Virus
There is still no specific treatment for or vaccine against WNV so decreasing risk of infection is important. The key to minimizing risk of infection is avoiding mosquito bites. People over 50 are at particular risk of harm from WNV. Avoiding outdoors at dusk and dawn, wearing DEET containing mosquito repellent and protective clothes, ensuring screens on windows and doors are intact, and emptying standing water from outdoor pots, buckets, and barrels are all important ways to keep mosquitoes at bay.
WNV is not going away any time soon and no vaccines are on the immediate horizon. Careful avoidance of mosquito bites is the most important way to avoid developing the WNV skin rash as well as the more serious and sometimes life-threatening manifestations of this infection.