Arboviral Disease in New Hampshire 2016

July 12, 2016

New Hampshire Division of Public Health Services (NH DPHS) recommends:

1. Vigilance during the summer months to consider mosquito-borne diseases, including West Nile virus (WNV) and eastern equine encephalitis (EEE), among patients with compatible clinical features. Laboratory confirmation should be arranged by calling (603) 271-4496 during business hours or (603) 271-5300 after hours. Forms and human testing information are available at

2. Remind patients to avoid mosquito bites by use of insect repellents and wearing protective clothing, and environmental reduction of mosquito populations.

3. Report all arboviral illnesses, confirmed or suspected, to the DPHS within 24 hours at 603-271-4496 (after hours 800-852-3345, ext. 5300).


Arboviruses transmitted in NH include WNV and EEE virus, both transmitted to humans through the bite of an infected mosquito. In 2013, the first human case of locally acquired Jamestown Canyon virus (JCV) was also identified. EEE and WNV are maintained in a bird-mosquito cycle with humans considered incidental hosts. JCV is maintained in a deer-mosquito cycle, and reports of human illness are rare. The greatest risk for human acquisition of arboviral diseases in NH is between July and October. Year-round transmission is possible in some geographic locations in the US.

Nationally during the last arboviral season (2015), there were 2,060 human cases of WNV reported, including 119 deaths. Neuroinvasive disease (meningitis and/or encephalitis) was recorded in 1,360 cases, while 700 cases were diagnosed with milder West Nile fever. There were also 5 human cases of EEE reported in the US. In NH, there were 3 WNV-positive mosquito batches, 1 veterinary case, and no human cases. For EEE, there were 2 EEE-positive mosquito batches.

While not transmitted locally in NH, Zika virus, chikungunya virus (CHIKV), and other arboviruses are possible among travelers returning from endemic regions. As of June 30, 2016, 4 travel- associated cases of Zika virus infection have been identified in NH. The Centers for Disease Control and Prevention (CDC) recently reported that the Zika virus mosquito vectors Aedes aegypti and Aedes albopictus were detected in NH. NH DPHS has not verified these detections and does not have evidence that there are sustained populations of these mosquitoes. NH DPHS is investigating the CDC report and enhancing efforts to detect these vectors. At this time, local transmission of Zika virus by mosquitoes should be considered extremely unlikely. The most recent Zika virus HAN can be found here:

When to Suspect Arboviral Illness

The incubation periods of both WNV and EEE following the bite of an infected mosquito range from 3 to 14 days. Most infections are asymptomatic or mild, including fever, headache, myalgias, and arthralgias. Approximately 20% of those infected with WNV develop a mild illness known as West Nile Fever. Neurologic infection is manifest by altered mental status and/or neurological dysfunction (cranial and peripheral neuritis or other neuropathies, including acute flaccid paralysis syndrome).

A minority of patients with severe disease develop a diffuse maculopapular or morbilliform rash. Approximately 1 in 150 WNV infections will result in severe neurological disease, with encephalitis more common than meningitis. Older patients are at increased risk of developing severe WNV infections. For EEE, approximately one-third of all people who develop clinical encephalitis will die from the disease. Among those who recover, many suffer from permanent brain damage. Severe disease can be seen in any age group, including children.

The typical laboratory findings of WNV and EEE are normal or elevated leukocytes, lymphopenia, anemia, and hyponatremia. Cerebrospinal fluid (CSF) exam may show pleocytosis (usually with a lymphocytic predominance), elevated protein, and normal glucose levels. For about one-third of WNV patients, magnetic resonance imaging (MRI) shows enhancement of the leptomeninges, the periventricular areas, or both, while MRI of EEE patients often reveals abnormalities of the basal ganglia and thalami.

Treatment is supportive, such as intravenous fluids, respiratory support, and prevention of secondary infections for patients with severe disease.

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:

a. Fever > 38.0⁰ C or 100⁰ F, and

b. Central nervous system 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

c. Abnormal CSF profile suggesting a viral etiology (a negative bacterial stain and culture) showing pleocytosis with predominance of lymphocytes. Elevated protein and normal glucose levels.

How to Report Suspect Cases of Arboviral Illness

All suspected arboviral cases should first be reported to the NH DPHS by telephone. A completed case report form must be faxed to the NH Infectious Disease Investigation Section (603-271-0545) and a copy submitted with the laboratory specimen(s) to the NH Public Health Laboratories (PHL). DPHS staff members are available 24/7 to help determine if the clinical presentation meets the case criteria and whether further testing would be appropriate.

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

Laboratory Testing for Arboviral Illnesses

Laboratory diagnosis of arboviral infections is generally accomplished by testing serum and/or CSF for virus-specific IgM and neutralizing antibodies. The NH PHL can test for EEE, WNV, and St. Louis encephalitis (SLE) IgM. Positive IgM results are sent to CDC for confirmatory testing.

The PHL can also test for Zika (IgM and viral RNA), CHIKV (PCR), and dengue (PCR). Please consult the Bureau of Infectious Disease Control at (603) 271-4496 prior to sending specimens to the PHL for these tests.

For more information, including specimen collection instructions, please refer to:

For additional information on WNV and EEE please refer to:

1. NH DHHS website

2. Centers for Disease Control, Division of Vector-Borne Infectious Diseases website

For questions, please call Bureau of Infectious Disease Control at (603) 271-4496 or 800-852-3345, extension 4496, during business hours (8 am to 4:30 pm). Nights or weekends call the NH Hospital switchboard at 800-852-3345, extension 5300, and request the Public Health Professional on-call.

For any questions regarding the contents of this message, please contact NH DHHS, DPHS, Bureau of Infectious Disease Control at 603-271-4496 (after hours, 800-852-3345, ext. 5300).


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