SOMERSET — Mosquitoes carrying the potentially deadly West Nile virus have been found in Somerset and Fall River, and officials who had planned to spray the area had to postpone the project Tuesday because of the weather.

In extreme cases, West Nile can cause headaches, high fever, neck stiffness, convulsions and paralysis. People older than 50 face the highest risk.

On Tuesday, officials in both communities announced that trapped mosquitoes had tested positive for the virus.

In Fall River, the mayor’s office said the spraying scheduled for Tuesday was delayed and would be done this morning, from 2 to 5 a.m. in the area of Danforth and Locust streets, where an infected mosquito was found.

In Somerset, the batch of mosquitoes collected from O’Neil Road tested positive. The town is being sprayed as well.

Health Agent Christina Wordell said spraying had been scheduled Tuesday as well, but she had not been able to immediately confirm if it had been delayed.

Somerset spraying is also scheduled for tomorrow, also between 2 and 5 a.m.

“It’s always the same time,” she said.

Residents are urged to keep their windows closed and not go outside during the spraying period.

Officials said yesterday that people can protect themselves by limiting activity from dusk to dawn, which is the peak biting time for many mosquitoes.

They should also, if possible, wear long sleeves, long pants and socks to limit possible biting sites and to use insect repellent with DEET (also known as N-diethyl-m-toluamide), permethrin (which should only be applied to objects such as clothing, not skin), picaridin (KBR 3023), IR3535 or oil of lemon eucalyptus [also know as p-methane 3, 8-diol or PMD.

DEET products should not be used on infants younger than two months. If used in older children, the concentration should be 30 percent or less.

Homeowners should also remove the standing water where mosquitoes lay their eggs and make sure screens are in good repair.

Massachusetts health officials also monitor the spread of West Nile through dead birds, particularly blue jays and crows. Dead birds should be reported to the state by calling 1-866-MASS WNV.

gemery@projo.com