Natural Selection- Lice

Natural Selection- Lice

I've come to make your head itchy!!

What are Lice?

Lice, nits, or cooties are (Pediculus humanus) are tiny insects that live in the fur and hair of mammals. They feed on skin, blood and other secretions. They cause itching, sores, and can spread diseases like typhus. #ewwwww

EWWWWWWWW

How do I get lice??

Lice is commonly spread through close contact and sharing items like hats, scarves, brushes, etc. Cleanliness has nothing to do with it, and just washing your hair doesn't get rid of them.

Multiple Choice

What kinds of relationship do we have with lice?

• predator-prey

• competition

• commensalism

• parasitism

• mutualism

Multiple Choice

T or F: Lice is caused by poor hygiene

• True

• False

Old school treatments

Up until the 1970's, lice treatments included grossed out parents picking out individual lice from their kids' head. Yes, really. They also used combs to pull out the eggs that the lice would stick onto the hairs. It took a long time and involved a lot of tears. But the alternative was shaving their heads.

New school treatments

Pyrethroids are chemicals produced by flowers that are a natural insecticide. The work by attaching to protein channels in the insect's nervous system and this prevents the nervous system from working. These have been put into "lice shampoos" to help get rid of the lice.

The first pump is normal. It allows sodium to enter the cell and the nerves work normally. The second pump is inactivated. The pyrethroid chemical blocked the pump. Sodium can not enter the cells so the nervous system can not work anymore.

Multiple Choice

How do products with Pyrethroids help treat lice?

• This chemical prevents their nervous system from working

• This chemical prevents the lice from being able to eat

• This chemical prevents the lice from being able to reproduce

A real head-scratcher!

Doctors and scientists noticed something strange. Starting in the 1990's, the pyrethroid-based compounds stopped working.

Rise of the "super lice"

No, they aren't super heros- they are lice that are resistant to being killed by the pyrethroid chemicals. They have differently-shaped pumps. The pyrethroid doesn't block their pumps, so their nervous systems can work normally.

Multiple Choice

How do you think the resistant lice got these differently-shaped pumps?

• They changed their pumps on purpose so they couldn't be blocked by the pyrethroids

• These lice were born with a differently-shaped pump as part of a natural variation

The purple represent the lice with normal pumps. The orange represents the resistant lice with the differently-shaped pumps. Examine the pictures. On the next slide, you are going to describe what happened to the lice population.

Open Ended

Describe what happened to the lice population.

They are evolving!

• There are a lot of lice.

• Variations in lice- some have normal pumps, some have different pumps.

• The lice with normal pumps were killed easily with the pyrethroid. Lice with different pumps were unaffected and survived.

• Lice with different pumps mated and passed on the genes to have different pumps to the baby lice. Now we can't kill the lice. Gross.

Multiple Choice

What process is allowing the lice to evolve?

• artificial selection

• natural selection

• use and disuse

Resistance in Lice over time

Examine this graph. It shows the percentage of lice cases that were resistant to pyrethroid. You will use this graph to answer the following few questions.

Suppose you use a pyrethroid product in 1983. What is the percent chance that the lice would be resistant to the pyrethroid product?

Multiple Choice

Suppose you use a pyrethroid product in 1983. What is the percent chance that the lice would be resistant to the pyrethroid product?

• 0% chance

• 15% chance

• 25% chance

Multiple Choice

Suppose you use the same pyrethroid product in 2001. What is the percent chance that the lice would be resistant to the pyrethroid product?

• 0% chance

• 15% chance

• 25% chance

This is becoming a big problem in the USA. The orange states show were they found at least some resistant lice in 100% of the samples they collected. Let's use this information. Suppose your head is feeling itchy and it turns out you have lice. What are the chances you will be able to kill the lice easily with an over-the-counter pyrethroid lice shampoo?

Multiple Choice

Suppose you have a lice infection right now. What are the chances you will be able to kill the lice easily with an over-the-counter pyrethroid lice shampoo?

• the pyrthroid shampoo will be effective and you will get rid of your lice problem soon- hooray!

• the pyrethroid shampoo will likely be ineffective and you are going to have to shave your head- sorry!

Alternative treatments

In Europe, people do not use pyrethroid shampoos anymore because they are ineffective. They use silicone and oils to "suffocate" the lice. Another common at-home remedy is covering your head in mayonnaise. At least it's better than shaving your head...

Suffocating the lice doesn't affect the nits, or the eggs they leave stuck on our hair. And when they hatch....you have your lice problem all over again!

Back to the drawing board!

Many people find themselves using a combination of treatments, including going back to old-school treatments to help their lice problems!