August 17, 2019
2 min read

Incidence of West Nile virus neuroinvasive disease increased 25% in 2018

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The incidence of West Nile virus neuroinvasive disease was approximately 25% higher in 2018 than the median annual incidence during the previous decade, according to study findings published recently in MMWR.

The CDC collects data on endemic arboviral diseases from state health departments, which report cases through ArboNET, the national arbovirus surveillance system. It logged a total of 2,813 cases of domestic arboviral disease in 2018, 94% of which were caused by West Nile virus (n = 2,647).

The remaining cases were caused by La Crosse virus (86 cases), Jamestown Canyon virus (41), Powassan virus (21), St. Louis encephalitis virus (8), eastern equine encephalitis (6) and unspecified California serogroup virus (4).

“Data from the recent MMWR on domestic arboviral diseases in the United States showed that 2018 was an above average year for West Nile virus,” Stacey W. Martin, MSc, an epidemiologist in the CDC’s Division of Vector-Borne Diseases, told Infectious Disease News. “Weather, mosquito abundance, bird infection rates, human behavior, and awareness and testing practices all influence annual variations in when and where West Nile virus cases and outbreaks occur. This can make it hard to assess why one year has more disease than another.”

The researchers noted that 93% of arboviral disease cases occurred between April and September 2018 — consistent with previous years.

According to Martin and colleagues, there were 1,658 cases of West Nile virus neuroinvasive disease reported in 2018, with cases of acute flaccid paralysis, encephalitis, meningitis or other unspecified neurologic presentation counted as neuroinvasive diseases. The rate was 0.51 per 100,000 people, nearly 25% higher than the median of 0.41 from 2008 to 2017.

Two West Nile virus disease cases were reported in solid organ recipients from a single donor, marking the first transplant-transmitted cases reported since 2013, they noted. Powassan virus disease was reported for the first time from Indiana in the first documented case of Powassan virus transmission via blood transfusion. This likely originated from a viremic donor in Wisconsin, the authors noted.

“Because arboviral diseases continue to cause serious illness and have no definitive treatment, maintaining surveillance is important to direct and promote prevention activities,” they wrote. “Health care providers should consider arboviral infections in patients with aseptic meningitis or encephalitis, perform appropriate diagnostic testing, and report cases to public health authorities.”

Martin and colleagues noted that ArboNET underreports the actual incidence of disease and does not require information about clinical signs and symptoms or laboratory findings, which may result in cases being misclassified. – by Joe Gramigna

Disclosures: The authors report no relevant financial disclosures.