Infectious Diseases / Outbreak Watch

Tick Borne Encephalitis Attributed to Powassan Virus in Canada

Hastings Prince Edward Public Health (HPEPH), in a media release, has reported that there is a suspected case of tick-borne encephalitis under investigation at their facilities. Tick borne encephalitis is a rare disease resulting in central nervous system manifestations and this case is thought to have been caused by Powassan Virus, a member of the Flaviviridae family. Human cases of Powassan virus cases have been reported few and far between and remain an exotic diagnosis at best, making this a rather rare and exceptional case.

The US CDC site states:

Powassan (POW) virus is an RNA virus that belongs to the genus Flavivirus. It is related to West Nile, St. Louis encephalitis, and Tick-borne encephalitis viruses.

Humans become infected with POW virus from the bite of an infected tick. Humans do not develop high enough concentrations of POW virus in their bloodstreams to infect feeding ticks. Humans are therefore considered to be “dead-end” hosts of the virus.

POW virus is maintained in a cycle between ticks and small-to-medium-sized rodents. In North America, three main enzootic cycles occur: Ixodes cookei and woodchucks, Ixodes marxi and squirrels, and Ixodes scapularis and white-footed mice. Ixodes cookei and Ixodes marxi rarely bite humans. Ixodes scapularis often bite humans and is the primary vector of Lyme disease.

There are two types of POW virus in the United States. The first type, often called lineage 1 POW virus, appears to be associated with Ixodes cookei orIxodes marxi ticks. The other type, lineage 2 POW virus is sometimes called Deer tick virus, and is associated with Ixodes scapularis ticks. Both lineages have been linked to human disease.

The HPEPH website has also outlined some effective preventive measures, which include the following advice:

Protect Yourself from Tick Bites

  • Avoid areas with a known high concentration of ticks. Ticks live in humid environments, including wooded and bushy areas with high grass and a bed of leaf litter. To avoid ticks, walk in the centre of the trails and avoid tall shrubs.
  • Wear protective clothing: light-coloured clothing, long-sleeved shirts and pants, closed-toe shoes and socks pulled over pant legs.
  • Use insect repellent containing DEET (active ingredient to keep bugs away) or Icaridin. Spray this on your skin as well as on your clothing. Always read and follow label directions.

Perform Daily Tick Checks

  • Check your body for ticks after being outdoors, even in your own yard.
  • Use a hand-held or full-length mirror to view all parts of your body.
  • Parents should check their children for ticks under the arms, in and around the ears, inside the belly button, behind the knees, between the legs, around the waist, and especially in their hair.
  • Examine your gear and pets. Ticks can ride into the home on clothing and pets, then attach to a person later. Placing clothes in a dryer on high heat effectively kills ticks.

Remove Ticks from Your Body

  • Remove an attached tick as soon as you notice it.
  • Use fine-tipped tweezers to grasp the tick by the head as close to your skin as possible. Pull it straight out, gently but firmly.
  • Clean the bite area using soap and water or a disinfectant.
  • If the tick has been attached for >36 hours or you begin to experience symptoms as noted above you should seek medical advice.

For more information, please visit http://www.hpepublichealth.ca/home/vector-borne-diseases

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