Naked Science Forum

Life Sciences => Plant Sciences, Zoology & Evolution => Topic started by: Ed Hertel on 22/10/2008 08:46:16

Title: Why can't mosquitoes transmit diseases like a dirty needle?
Post by: Ed Hertel on 22/10/2008 08:46:16

Ed Hertel asked the Naked Scientists:

In the 22 Aug show, Dr. Dave explained that mosquitoes cannot transmit HIV because the disease cannot grow and propagate in the insect's stomach like malaria.

If this is true, how is it possible that a used needle is able to transmit the disease so easily?  Wouldn't a dirty mosquito proboscis act in the same way as a dirty needle?

What do you think?

Title: Why can't mosquitoes transmit diseases like a dirty needle?
Post by: lyner on 28/10/2008 14:25:51

Mosquitos probably have an immune system which actively damages the virus where a needle doesn't.
They have developed a working relationship with the Malaria parasite so they don't kiil it.

Title: Why can't mosquitoes transmit diseases like a dirty needle?
Post by: Bored chemist on 28/10/2008 18:44:00

Male mosquitos don't bite people- they feed on plants. Female mosquitos only bite people to get blood in order to provide protein and iron for their eggs. They don't do this often so, in most cases, any mosquito that has drawn blood from one person doesn't need to bite a second person.

Enough diseases are spread by mosquitos to show that we are sometimes plain unlucky.

Title: Why can't mosquitoes transmit diseases like a dirty needle?
Post by: chris on 28/10/2008 19:03:40

Size is mainly the reason that a needle, but not a mosquito, can transmit HIV and other viruses. A mosquito's proboscis (mouthparts) are a fraction of a millimetre across whilst a small needle is over ten times wider. This means that the volume of blood that can be carried within a needle, and hence the infectious viral load, will be far greater than a mosquito's proboscis.

The reason that malaria (a protozoal infection) and certain viruses like dengue fever or Chikungunya can be transmitted by mosquitoes is that these infections have evolved to replicate within the body of the mosquito. This boosts the infectious load, compensating for the tiny number of organisms pulled into the mosquito's body when it first bit. This infectious load is transmitted with the next meal.

Chris

Title: Why can't mosquitoes transmit diseases like a dirty needle?
Post by: blakestyger on 28/10/2008 21:01:04

If the amount of material injected by the insect is below the infectious viral load what happens to the viruses that prevents them from replicating to become sufficient in number to infect?

Thanks

Title: Why can't mosquitoes transmit diseases like a dirty needle?
Post by: chris on 29/10/2008 08:59:38

HIV is quite fragile and is not adapted to survive within the environment of the insect's gut. Consequently, even if the source patient had a viral load in the billions (as some occasionally do), the particles would be denatured within the insect's digestive system.

Chris

Title: Why can't mosquitoes transmit diseases like a dirty needle?
Post by: blakestyger on 29/10/2008 14:33:22

Thank you Chris - it seems that the quality of the viral protein coat varies from species to species.