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Insect-borne viruses take toll on Americans

Incidence of reported cases of West Nile virus neuroinvasive disease per 100,000 population, by state, in 2013.

Incidence of reported cases of West Nile virus neuroinvasive disease per 100,000 population, by state, in 2013.

Mosquito-borne viruses may pose a threat to America’s horses, but they’re no walk in the park for humans either, a study shows.

Researchers with the US Centers for Disease Control and Prevention have shone a spotlight on the 2605 cases of insect-borne diseases among humans in the US during 2013, with West Nile Virus (WNV) being by far the most prevalent.

Nicole Lindsey, Jennifer Lehman, Erin Staples and Marc Fischer found that 47 states and the District of Columbia reported 2469 cases of West Nile Virus (WNV) disease. Of these, 1267 – that’s 51 percent – were classified as neuro-invasive, for a national incidence of 0.40 per 100,000 people.

After WNV, the next most commonly reported insect-borne disease was La Crosse virus (LACV), with 85 cases, followed by Jamestown Canyon virus (JCV) with 22 cases, Powassan virus (POWV) with 15 cases, and eastern equine encephalitis virus (EEEV), with 8 cases.

Lindsey and her colleagues said WNV and other arboviruses continued to cause serious illness in substantial numbers of persons annually.

Maintaining surveillance remained important to help direct and promote prevention activities, they said.

The primary insect vectors were mosquitoes and ticks.

They said while most human infections with insect-borne viruses were asymptomatic, those who did develop symptoms usually showed a fever or neuro-invasive disease.

The 2605  cases of nationally notifiable insect-borne viral diseases in 2013 were reported from 830 (26 percent) of the 3141 US counties. No cases were reported from Alaska or Hawaii.

Of the 2605 cases, 1383 (53 percent) were reported as neuro-invasive, for a national incidence of 0.44 per 100,000 population.

WNV cases were reported from 725 counties in 47 states and the District of Columbia.

Mosquitoes like this female Aedes (Ochlerotatus) sp., sucking blood to get nourishment for her eggs, can transmit the viruses that cause West Nile fever and Rift Valley fever.

Mosquitoes like this female Aedes (Ochlerotatus) sp., sucking blood to get nourishment for her eggs, can transmit the viruses that cause West Nile fever and Rift Valley fever.

WNV cases peaked in early September, with 90 percent of cases having illness onset during July–September. The median age of patients was 55 years. A total of 119 patients (5 percent) died. The median age of patients who died was 78

States with the highest WNV disease incidence rates included North Dakota (8.9 per 100,000), South Dakota (6.8), Nebraska (2.9), and Wyoming (2.8).

Six states reported abouot half (51 percent) of the WNV neuroinvasive disease cases: California (237 cases), Texas (113), Colorado (90), Illinois (86), North Dakota (64), and Oklahoma (60).

The researchers noted that eastern equine encephalitis virus cases, although rare, remained the most severe insect-borne disease, with four deaths among the eight 2013 sufferers patients.

“More than 90 percent of arboviral disease cases occurred during April–September, emphasizing the importance of focusing public health interventions during this period.”

They noted that the incidence of WNV neuro-invasive disease declined substantially in 2013 – 0.40 per 100,000 people, compared with 2012′s 0.92 per 100,000 people – when a large multi-state outbreak occurred.

However, the incidence in 2013 was similar to that during 2004–2007.

The study findings can be read in full here.

Horsetalk.co.nz

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