West Nile Virus Detected in Mosquitos in New Hampshire

August 10, 2017

Key Points and Recommendations:

1. The first detections of West Nile Virus (WNV) in New Hampshire for 2017 have occurred in two mosquito batches from Manchester, New Hampshire (NH).

2. Healthcare providers should consider mosquito-borne diseases, including WNV and Eastern Equine Encephalitis (EEE), in patients presenting with compatible clinical syndromes regardless of the presence or absence of positive mosquito or veterinary testing in their community.

3. Residents and visitors of NH should take steps to prevent mosquito bites by wearing protective clothing, applying insect repellents, and reducing environmental mosquito populations around their homes.

4. Laboratory testing for mosquito-borne diseases can be arranged by calling 603-271-4496 during business hours or 603-271-5300 after hours. Testing information is also available on the state Department of Health and Human Services (DHHS) website.

5. Healthcare providers should report suspected and confirmed cases of mosquito-borne diseases to the NH Bureau of Infectious Disease Control at 603-271-4496 (after hours, 603-271-5300).


From the beginning of July through mid-October, the NH DHHS supports local communities to trap and test mosquitos for WNV and EEE to help determine if these viruses are circulating in local mosquito populations. NH DHHS has identified the first two WNV-positive mosquito batches (collection of mosquitos) of the 2017 arboviral season. The mosquitos were trapped in Manchester, NH, on July 31, 2017, and August 1, 2017. Identification of WNV in mosquitos highlights the importance of preventing mosquito bites. In 2016, there were no human or animal cases of WNV, and one positive mosquito batch in Nashua, NH. For EEE in 2016, there were no human, animal, or mosquito batches that tested positive. There have been no EEE detections in NH yet in 2017.

Mosquito trapping and testing occurs at limited sites primarily in the southern and southeastern parts of NH; the absence of positive mosquito tests does not mean that WNV and EEE are not potentially circulating in your local communities. There have been detections of WNV and EEE throughout NH in prior years, including areas outside of where mosquito surveillance is currently focused. Healthcare providers should consider testing patients for mosquito-borne diseases, including WNV and EEE in patients who present with compatible clinical syndromes.

Mosquito-borne diseases are preventable. The NH DHHS recommends that communities:

  • Maintain/enhance surveillance efforts including mosquito batch collection and submission to the NH Public Health Laboratories for testing,

  • Educate community members on the public health effects of mosquito-borne diseases and the effective personal protection methods of preventing mosquito-bites (fact sheets, posters, and PowerPoint Presentations for cable access programs are available on the DHHS website,

  • Develop, maintain, and implement a local mosquito control plan to address preparation and response to mosquito-borne diseases, including public education, surveillance, and mosquito control. The State plan is available at the website listed above and can be used as a template for local communities.

When to Suspect Arboviral Illness

Please refer to the Arboviral Illness Health Alert Network message sent in June for more clinical information and specimen submission instructions.

Laboratory testing for WNV, EEE, St. Louis encephalitis, Chikungunya virus, and Zika virus is available at the NH Public Health Laboratories (PHL). Testing for other arboviral diseases, such as Powassan virus and Jamestown Canyon virus, is available at the Centers for Disease Control and Prevention (CDC). Testing arrangements should be made in consultation with NH DHHS. Please call the Bureau of Infectious Disease Control at 603-271-4496 (after hours, 603-271-5300).

When to Report Suspected Cases of Arboviral Illness

Clinicians, hospitals, and laboratories should report within 24 hours any patient meeting the following criteria:

1. Any patient with encephalitis or meningitis from July through November, who meet criteria a, b, and c below without an alternative diagnosis:

  1. Fever > 38.0° C or 100° F, and

  2. CNS involvement including altered mental status (altered level of consciousness, confusion, agitation, lethargy) and/or other evidence of cortical involvement (e.g., focal neurologic findings, seizures), and

  3. Abnormal CSF profile suggesting a viral etiology (e.g., a negative gram stain and culture, cell count with a lymphocyte predominance, elevated protein, and normal glucose levels).

How to Report Suspect Cases of Arboviral Illness

All suspected arboviral cases should be reported to the NH DHHS by telephone at 603-271-4496 (after hours, 603-271-5300). A completed case report form must be faxed to the NH Infectious Disease Investigation Section (603-271-0545) and a copy should be submitted with the laboratory specimen(s) to the NH Public Health Laboratories. Staff members are available 24/7 to help facilitate testing.

For additional information on arboviral illness and maps of recent activity, please visit the NH DHHS website. The website also has fact sheets on WNV and EEE.

For additional information on WNV and EEE please refer to:

1. NH DHHS website

2. CDC Division of Vector-Borne Infectious Diseases website

3. FAQs about WNV published by the American Society for Microbiology

For any questions regarding the contents of this message, please contact NH DHHS Bureau of Infectious Disease Control at 603-271-4496 (after hours, 603-271-5300).


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