Saturday 20 August 2016

Tests and temps...

From [10]
It's been about 5 weeks since Brazil updated its microcephaly-related-to-Zika-virus reporting index page. 

The last post listed (a couple of others made their way out via other channels) was from epidemiological week (EW) No. 26. 

For comparison, Colombia is about to post data for EW No. 32. [12]

Interestingly, Colombia's National Institute of Health has not seen any new laboratory confirmed Zika virus disease cases during that same period - so perhaps Brazil is not seeing any either?

Temperature graphs (in Celsius) from
Top-Miami Beach, Florida.
Bottom-Rio de Janeiro, Brazil
Meanwhile, more of the US state of Florida is seeing local Zika virus spread.[4,5,6] If we look at the temperature graphs we can see that Miami Beach (around 32'C)  is certainly a lot warmer and holding more steady than Rio (around 24'C) in August 2916. 

High and fluctuating temperatures are important for flavivirus multiplication in mosquitoes but for the mosquitoes themselves, particularly Aedes aegypti, they can live for about the same period (around 3 weeks) when conditions suit, whether at 26'C or 30'C.[12,13]

As I was recently taught by Rebbeca C Christofferson and Anthony Willson, viral loads do better in mosquitoes living at an optimal temperature. But when more Dengue virus for example, is replicating throughout the mosquito, that can have an effect on the length of their lives, even if not having an immediate impact on mortality.[14]

When you stop and think about it there is a lot going on for a mosquito when it takes a big blood meal. 

There could be a huge rapid weight gain, and there can be a 20'C temperature difference between the host's blood and the insect's temperature - that's a big shock at any size! There is also a big osmotic imbalance (difference in osmotic pressure due to the concentration of dissolved solids in the host's blood versus that in the insect's hemolymph [8,9]) and there's a need to get rid of toxic metabolites.[1] 

Have you seen that big drop of excreted fluid attached to some species of mosquito's butt? It appears once feeding has started and is something they excrete (urine and concentrated red blood cells; a process called prediuresis) to help them balance osmolarity, offset weight gain and sometimes to regulate their temperature through evaporation.[2,7] 

Some mosquito species retain the drop ('drop-keeping') making use of evaporative cooling, some emit new drops.[7] As far as I can tell so far, Aedes species don't make use of the drop for cooling. Male mosquitoes don't heat up because they don't feed on blood so they rely on environmental temperatures for heating and cooling.[7]

So much more reading to be done (apologies for errors above - I'm still learning about mozzies) - just not of data from Brazil.

  1. Thermal Stress and Thermoregulation During Feeding in Mosquitoes

No comments:

Post a Comment

Note: only a member of this blog may post a comment.