Following the discovery of a horse infected with the West Nile virus in Aldergrove last week and another infected horse in the South Okanagan, provincial health officials are urging people to take preventative measures to protect themselves and their horses.

Dr. Paul Kitching, chief veterinarian and branch director at the Animal Health Centre, said in a release West Nile's arrival in B.C. was expected, but action still needs to be taken.

"This is not a surprising development," he said.

"British Columbia has long anticipated the arrival of West Nile virus, and now it's in multiple regions of the province.

What is important is preventing infection as best as possible, for both humans and animals.

"Of all large land mammals, horses are particularly susceptible. There are West Nile virus vaccines for horses, and horse owners should talk to their vets about getting their animals immunized," he said.

Infected horses cannot directly infect other horses or humans. However, they indicate the presence of mosquitoes carrying the disease, which may pose a threat to other horses and humans in the area. In addition to getting their animals vaccinated against the disease, horse owners are urged to practice mosquito control to limit this risk, especially by draining pools of standing water where mosquitos breed.

Dr. Bonnie Henry, director of the Vector-Borne Disease Program at the British Columbia Centre for Disease Control, said in a release there is no vaccine available for humans at this time, so people should do what they can to avoid mosquito bites.

"Common-sense precautions against getting bitten by mosquitoes should be taken, especially when outdoors, and even as we head into the fall," she said.

"This includes wearing light-coloured, long-sleeved shirts and long pants — especially in the evenings and early mornings when mosquitoes are most active — and using mosquito repellents that are federally registered, such as those that contain DEET and lemon eucalyptus oil."

The West Nile virus is transmitted by mosquitoes, who become ill by feeding on infected birds and then carry the virus to people, animals and other birds. Some of the animals and most of the people who become infected will be symptom-free, but around 20 per cent of infected people will develop fever, rash and headache symptoms.

One in every 150 human cases can cause more serious neurological complications, such as encephalitis (inflammation of the brain) and meningitis (infection of the lining of the brain). Some animals may develop fever, muscle spasms, weakness, lack of co-ordination, seizures and changes in behaviour. For horses in particular, symptoms can include stumbling, weakness, head pressing, confusion, inability to stand, seizures and listlessness.

Dr. Elizabeth Brodkin, medical health officer for Fraser Health Authority, said in a release that the health authority is watching out for signs of infected animals.

"We have a well-established surveillance program in the Fraser Valley, and so far we have had no positive mosquitoes or birds in the area," she said.

"But the case of this infected horse indicates that the virus is here. We are reminding people in the Fraser Health region to continue to take precautions to prevent mosquito bites as the best way to protect themselves and their families from West Nile virus."

Fraser Health is also requesting that local residents keep their eyes peeled for dead birds, particularly crows, ravens, magpies and jays, and report them to the authority.