Dr C James Hospedales, MB BS,

MSc, FF­PH  

Jameshospedales@earth­medic.org

Did you know the world’s dead­liest an­i­mal is the mos­qui­to? An­nu­al­ly, mos­qui­toes cause up to one mil­lion deaths glob­al­ly be­cause of the dis­eases they trans­mit. Un­like snakes or sharks, mos­qui­toes do not kill di­rect­ly. In­stead, they spread in­fec­tions that can cause se­ri­ous ill­ness and death in hu­mans.  

I know this per­son­al­ly. I’ve had dengue and Zi­ka, and mem­bers of my fam­i­ly have suf­fered se­vere dengue fever and chikun­gun­ya, which is mak­ing a come­back. These ill­ness­es are not ab­stract threats; they are part of our lived ex­pe­ri­ence in T&T and the Caribbean.  

Un­der­stand­ing how mos­qui­toes spread dis­ease—and how cli­mate change wors­ens the prob­lem—can help all of us.  

What are vec­tor-borne dis­eases?  

Vec­tor-borne dis­eases are ill­ness­es trans­mit­ted to hu­mans by or­gan­isms known as “vec­tors.” A vec­tor is an or­gan­ism that car­ries a germ (eg, a virus or par­a­site) from one host to an­oth­er.  

Mos­qui­toes are the most im­por­tant dis­ease vec­tors world­wide. In the Caribbean, the fa­mil­iar Aedes ae­gyp­ti mos­qui­to spreads sev­er­al dis­eases, in­clud­ing dengue fever, chikun­gun­ya and Zi­ka.  

When a mos­qui­to bites an in­fect­ed per­son, it can pick up the virus in that per­son’s blood. Af­ter the virus mul­ti­plies in­side the mos­qui­to, it can trans­mit the virus to the next per­son it bites. In this way, mos­qui­toes act as fly­ing sy­ringes, spread­ing dis­ease from per­son to per­son.  

Dengue in­fects over 100 mil­lion peo­ple each year world­wide. While many cas­es are mild, some de­vel­op in­to se­vere dengue, which can cause bleed­ing, or­gan fail­ure and death.  

Low-in­come com­mu­ni­ties are at high­er risk if many peo­ple live in prox­im­i­ty, lack pipe-borne wa­ter, don’t have in­sect screens, and are far from health ser­vices.  

Cli­mate change is ex­pand­ing risk 

Cli­mate change is not just an en­vi­ron­men­tal is­sue—it is a health is­sue. Ris­ing tem­per­a­tures, chang­ing rain­fall and more ex­treme weath­er events in­flu­ence mos­qui­to pop­u­la­tions and the dis­eases they car­ry. Mos­qui­toes are cold-blood­ed, mean­ing their body tem­per­a­ture de­pends on the en­vi­ron­ment. As tem­per­a­tures in­crease, sev­er­al things make dis­ease spread more like­ly.  

For trop­i­cal re­gions like the Caribbean—where tem­per­a­tures al­ready favour mos­qui­to sur­vival—even small in­creas­es in tem­per­a­ture can sig­nif­i­cant­ly af­fect dis­ease trans­mis­sion.  

First, warmer con­di­tions al­low mos­qui­to lar­vae to grow in­to adults more quick­ly, in­creas­ing mos­qui­to pop­u­la­tions.  

Sec­ond, virus­es in­side mos­qui­toes mul­ti­ply faster in warmer tem­per­a­tures. This short­ens the time be­tween a mos­qui­to pick­ing up a virus and when it can in­fect an­oth­er per­son.  

Third, warmer tem­per­a­tures of­ten ex­tend the ge­o­graph­ic range of mos­qui­toes. Ar­eas that were pre­vi­ous­ly too cool for Aedes mos­qui­toes may now be­come suit­able.  

Cli­mate change al­so in­flu­ences rain­fall. Heavy rain can cre­ate more stand­ing wa­ter—per­fect breed­ing sites for mos­qui­toes. At the same time, drought can lead peo­ple to store wa­ter in tanks, bar­rels, or drums at home, which can be­come mos­qui­to breed­ing sites if not prop­er­ly cov­ered.  

Why warmer days and nights mat­ter  

Sci­en­tists are in­creas­ing­ly recog­nis­ing the im­por­tance of warmer nights as well as warmer days.  

Aedes mos­qui­toes tend to bite dur­ing day­light, par­tic­u­lar­ly ear­ly in the morn­ing and late in the af­ter­noon. But warmer nights im­prove mos­qui­to sur­vival and al­low virus­es in­side mos­qui­toes to de­vel­op more quick­ly.  

When both days and nights are warmer, your body al­so sweats more. Mos­qui­tos are more at­tract­ed to hot and sweaty skin be­cause of am­mo­nia and oth­er chem­i­cals in per­spi­ra­tion, in­creas­ing the like­li­hood of be­ing bit­ten.  

What can we do?  

There is a great deal we can do to re­duce mos­qui­to-borne dis­ease risk.  

Stay in­formed

Pay at­ten­tion to pub­lic health ad­vi­sories about dengue, chikun­gun­ya and oth­er mos­qui­to-borne dis­eases. Ear­ly aware­ness helps peo­ple recog­nise symp­toms and seek med­ical care quick­ly.  

Pro­tect your­self from mos­qui­to bites

Use in­sect re­pel­lents, es­pe­cial­ly dur­ing peak mos­qui­to ac­tiv­i­ty times. Light-coloured cloth­ing that cov­ers arms and legs can help re­duce bites. Win­dow screens, mos­qui­to nets and fans help re­duce ex­po­sure in­doors. 

Elim­i­nate mos­qui­to breed­ing sites around homes

This is one of the most ef­fec­tive steps in­di­vid­u­als and com­mu­ni­ties can take. Aedes mos­qui­toes breed in sites such as:  

Wa­ter stor­age drums and tanks that are not tight­ly cov­ered

Flow­er­pots and plant saucers  

Dis­card­ed tyres  

Buck­ets, bot­tles and con­tain­ers left out­doors

Blocked drains or gut­ters  

Even a small amount of wa­ter can pro­duce hun­dreds of mos­qui­toes. Reg­u­lar­ly emp­ty­ing, clean­ing or cov­er­ing con­tain­ers great­ly re­duces mos­qui­to pop­u­la­tions.  

Work to­geth­er as com­mu­ni­ties

Mos­qui­to con­trol is most ef­fec­tive when en­tire neigh­bour­hoods par­tic­i­pate. Com­mu­ni­ty clean-up cam­paigns and prop­er waste man­age­ment can elim­i­nate many breed­ing sites.  

Cli­mate ac­tion is health pro­tec­tion  

Fi­nal­ly, ad­dress­ing cli­mate change is es­sen­tial. Tran­si­tion­ing off fos­sil fu­els and strength­en­ing cli­mate re­silience will help lim­it the en­vi­ron­men­tal changes that al­low mos­qui­to-borne dis­eases to spread.  

The cli­mate and health cri­sis may feel over­whelm­ing, but every ac­tion mat­ters—from glob­al pol­i­cy changes to sim­ple steps in our own homes.  

The mos­qui­to may be the world’s dead­liest an­i­mal. But with knowl­edge, vig­i­lance, and col­lec­tive ac­tion, we can re­duce its im­pact and pro­tect the health of our fam­i­lies and com­mu­ni­ties.

The fore­go­ing is a week­ly col­umn by Earth­Medic and Earth­Nurse NGO to help read­ers un­der­stand and ad­dress the cli­mate and health cri­sis.