Ray­mond Ram­char­i­tar

T&T is in the midst of a chikun­gun­ya epi­dem­ic, which ex­pos­es the weak­ness of the na­tion­al ca­pac­i­ty to deal with such new sce­nar­ios. But the coun­try has a trump card many oth­ers don't, in UWI's Prof Dave Chadee, a world ex­pert on vec­tor-borne dis­eases.

Chadee is a Trinida­di­an en­to­mol­o­gist and par­a­sitol­o­gist who worked at the Min­istry of Health for two decades. His work in vec­tor con­trol is used the world over, and re­cent­ly he worked on the epi­demi­ol­o­gy and con­trol of chikun­gun­ya dur­ing out­breaks in the In­di­an Ocean is­lands. He is a con­sul­tant for the In­ter­na­tion­al Atom­ic En­er­gy Agency, the In­ter­gov­ern­men­tal Pan­el on Cli­mate Change, the World Health Or­gan­i­sa­tion and has been award­ed grants by the Bill and Melin­da Gates Foun­da­tion, among oth­ers, for his sci­en­tif­ic re­search. He is al­so the An­tho­ny N Sab­ga Caribbean Awards for Ex­cel­lence Lau­re­ate in Sci­ence & Tech­nol­o­gy for 2013.

The bad news about the present pub­lic-health threat, says Chadee, has two com­po­nents. First, our sus­cep­ti­bil­i­ty to in­fec­tion; and sec­ond, our abil­i­ty to con­trol its spread.

"With jet air­craft, huge ships and con­tain­er car­go," he says, "we have a sit­u­a­tion where peo­ple who are in­fect­ed in one part of the world can be trans­port­ed to an­oth­er part of the world with­in 24 hours. That means that they may have ac­quired the in­fec­tion but do not dis­play the symp­toms for up to a week af­ter their ar­rival in the new coun­try and these large ships can trans­port nu­mer­ous mos­qui­to vec­tors."

Such in­fec­tions with short in­cu­ba­tion pe­ri­ods can cause ma­jor dis­ease out­breaks in coun­tries which are com­plete­ly un­pre­pared. Chikun­gun­ya is a per­fect ex­am­ple, says Chadee.

"It is an African-Asian dis­ease, which was brought to the Caribbean by a viremic per­son, and with the pres­ence of Aedes ae­gyp­ti mos­qui­toes, trans­mis­sion was easy, and that led to the ex­plo­sive sit­u­a­tion."

The sit­u­a­tion is "ex­plo­sive" be­cause we have nev­er had chikun­gun­ya, and the whole pop­u­la­tion is "im­muno­log­i­cal­ly na�ve." Peo­ple in South­east Asia may have had the dis­ease be­fore, and are there­fore im­mune to a sec­ond bout. But here, says Chadee, where peo­ple have no re­sis­tance, "The in­fec­tions can spread like wild­fire. It's like a for­est with dead wood; you strike a sin­gle match, it all goes up in flames."

And this is not the ex­tent of the prob­lems. "We have no means of de­tect­ing in­fect­ed per­sons be­fore they man­i­fest symp­toms, and the low lev­el of vec­tor con­trol has led to an in­crease in the vec­tor den­si­ty (in this case the mos­qui­to). So the vec­tor den­si­ty (the num­ber of mos­qui­toes present) is very high and med­ical in­sti­tu­tions have lit­tle or no prac­ti­cal knowl­edge of clin­i­cal di­ag­no­sis and man­age­ment."

Vec­tor den­si­ty can be used to de­rive a "trans­mis­sion thresh­old," which is the min­i­mum num­ber of mos­qui­toes need­ed for the dis­ease to spread, and this should in­form the con­trol pro­gramme. T&T has not had enough time to work out the trans­mis­sion thresh­old for chikun­gun­ya, but if the pop­u­la­tion is sus­cep­ti­ble, as they cur­rent­ly are, a low vec­tor den­si­ty or trans­mis­sion thresh­old will be re­quired, while if the pop­u­la­tion is im­mune to the in­fec­tion, the trans­mis­sion thresh­old re­quired will be high for mos­qui­toes which can on­ly trans­mit the virus when a sus­cep­ti­ble per­son is bit­ten. These fac­tors are caus­ing the dis­ease to spread quick­ly be­cause the en­tire pop­u­la­tion can be con­sid­ered sus­cep­ti­ble to chikun­gun­ya and the vec­tor den­si­ty, or Breteau in­dex, is over ten in most ar­eas of T&T.

The coun­try is not help­less, but the sit­u­a­tion is sober­ing.

Chadee worked at the Min­istry of Health be­fore go­ing to UWI, and is aware of its pro­to­cols and lim­i­ta­tions. The pub­lic health re­sponse, un­for­tu­nate­ly, seems ham­strung by in­ef­fec­tive tech­nolo­gies. There has been an on­go­ing vec­tor con­trol pro­gramme since 1976, but for many years, he says, it suf­fered for lack of ma­te­ri­als, and many of the strate­gies that are cur­rent­ly used were strate­gies of the 70s and 80s and new ones have not been im­ple­ment­ed. Many of the chem­i­cals and the tech­nol­o­gy be­ing used have not been eval­u­at­ed giv­en the ev­i­dence of re­sis­tance of mos­qui­toes to in­sec­ti­cides.

For ex­am­ple, says Chadee, there is no ev­i­dence that "truck spray­ing" has any ef­fect on mos­qui­to con­trol. It might be used like a place­bo–see­ing the trucks might make peo­ple feel bet­ter–but it achieves noth­ing else. How­ev­er, he says, re­searchers at UWI de­vel­op ev­i­dence-based pub­lic health strate­gies which are avail­able to gov­ern­ment.

First and fore­most, the most ef­fec­tive weapon is in­for­ma­tion; be­cause there are things the gov­ern­ment can­not do. Strate­gies which should be con­sid­ered in­clude "tar­get­ed source re­duc­tion," in which on­ly the pri­ma­ry breed­ing grounds are ex­am­ined. This means, says Chadee: "We need to look at the con­tain­ers that are pro­duc­ing the most adult mos­qui­toes. We need to be look­ing at the wa­ter tanks, the basins, the wash­tubs, any large con­tain­ers, in­clud­ing tyres, that can hold a lot of wa­ter. The small cans and pans out in the sun­shine reach tem­per­a­tures that kill the lar­vae, so re­mov­ing those small con­tain­ers achieves lit­tle ex­cept that it makes the en­vi­ron­ment more aes­thet­i­cal­ly pleas­ing."

Since truck spray­ing has proven in­ef­fec­tive, large-scale gov­ern­ment mea­sures like "dy­na-fog­ging" can be used to spray in­doors and out­doors. Mos­qui­toes al­so rest in dark ar­eas be­low hous­es and in veg­e­ta­tion. So those kinds of ma­chines would be best for ap­ply­ing in­sec­ti­cides to those en­vi­ron­ments.

As for in­di­vid­ual house­hold­ers, says Chadee, "We have found that in­door spray­ing is very ef­fec­tive for the con­trol of Aedes. Stud­ies con­duct­ed in Trinidad and some Latin Amer­i­can coun­tries show that these mos­qui­toes rest un­der beds, in cup­boards, and dark places. So if those rooms are tar­get­ed for resid­ual spray­ing (spray­ing the walls) that would be a re­al­ly good strat­e­gy for pre­vent­ing the spread."

There is al­so a so­cial di­men­sion to dis­ease trans­mis­sion. Some com­mu­ni­ties are more sus­cep­ti­ble than oth­ers. The phe­nom­e­non of un­planned hous­ing com­mu­ni­ties in close prox­im­i­ty to swamps, forests and low-ly­ing ar­eas in­creas­es the risk of these com­mu­ni­ties to vec­tor-borne dis­eases. A good ex­am­ple, says Chadee, is in Ca­roni, where peo­ple set­tle near rice fields that car­ry large pop­u­la­tions of vec­tors like Anophe­les which trans­mits malar­ia.

Oth­er ar­eas, like Bel­mont, Mor­vant and so on, have not seen a lot of vec­tor con­trol work be­cause of the is­sue of the safe­ty of work­ers. Con­se­quent­ly, these ar­eas may have not been treat­ed for years and the mos­qui­to den­si­ty may be rel­a­tive­ly high. In oth­er, poor­er ar­eas, there might not be much will to en­force com­mon-sense strate­gies to de­stroy breed­ing grounds (like bar­rels, con­tain­ers and tyres in yards and emp­ty lots). "But re­cent stud­ies have shown mos­qui­toes oc­cu­py­ing atyp­i­cal habi­tats, ar­eas where we don't ex­pect them, such as sep­tic tanks, un­der­ground drains and flood­ed base­ments, which fur­ther com­pli­cate the vec­tor-con­trol task," says Chadee.

But it's not just low­er-in­come ar­eas that are at high risk. Plan­ning anom­alies have left high­er-in­come com­mu­ni­ties sus­cep­ti­ble to dis­ease based on where the new com­mu­ni­ties were and are sit­ed. This in­cludes clear­ing forest­ed ar­eas, and re­claim­ing marsh­lands. To com­bat this, says Chadee, "We need to bet­ter plan where hous­ing com­mu­ni­ties should be lo­cat­ed. There should be strict rules and cri­te­ria for hous­ing and de­vel­op­ment."

In the here and now, though, the chikun­gun­ya in­fec­tion is in its ear­ly stages. But it's not go­ing away: "Think of it like an ice­berg. You on­ly see a small part of the ice­berg on the sur­face of the wa­ter. In epi­demics, you on­ly see a third of the cas­es, so if Trinidad re­ports 1,000 cas­es, it's re­al­ly 3,000. In the Latin Amer­i­ca and the Caribbean re­gion, I've seen a fig­ure of about one mil­lion re­port­ed cas­es, so that means three mil­lion cas­es in all."

How­ev­er, there is some small rea­son for hope. As pop­u­la­tions be­come more ed­u­cat­ed through health pro­grammes and as so­cial me­dia are em­ployed, in­di­vid­u­als can play a greater role in their own health care and com­mu­ni­ty main­te­nance. In ad­di­tion, says Chadee, "There still re­mains a cadre of well-trained work­ers at­tached to the vec­tor con­trol unit (of the Health Min­istry). We need to up­grade their skills and keep them mo­ti­vat­ed, so the changes that are re­quired in the 21st cen­tu­ry can be im­ple­ment­ed."

Ad­di­tion­al­ly, Chadee's re­search team has for­mu­lat­ed new strate­gies, like ir­ra­di­at­ing male mos­qui­toes and re­leas­ing them in­to the wild, to de­crease pop­u­la­tion den­si­ties, and is de­vel­op­ing new traps and oth­er en­vi­ron­men­tal in­ter­ven­tions.

More in­fo

For a bi­o­graph­i­cal video and de­tailed in­ter­view with Prof Chadee, please vis­it the Face­book page and YouTube chan­nel for the An­tho­ny N Sab­ga Caribbean Awards for Ex­cel­lence.

Tips from Min­istry of Health­for chikun­gun­ya

�2 Dis­pose of all un­want­ed con­tain­ers/items in the yard or en­vi­rons which may col­lect wa­ter and be­come mos­qui­to breed­ing grounds.

�2 Cov­er wa­ter con­tain­ing con­tain­ers such as bar­rels, drums or buck­ets with a mos­qui­to proof cov­er­ing.

�2 En­sure that your drains and gut­ter­ing al­low the free flow of wa­ter.

�2 Emp­ty and scrub the sides of wa­ter vas­es or use dirt or sand in­stead to sup­port flow­ers.

�2 Cov­er ex­trem­i­ties when out in the evenings.

�2 Use bed nets that are tight­ly tucked un­der the mat­tress for pro­tec­tion at night.

�2 Use in­sect re­pel­lant that con­tains DEET as an ac­tive in­gre­di­ent.

Signs and symp­toms of chikun­gun­ya

�2 High fever (over 39 de­grees C)

�2 Se­vere joint pain (Can be­come chron­ic in peo­ple with pre-ex­ist­ing con­di­tions)

�2 Headache

�2 Back pain

�2 Mus­cle pain

�2 Rash

�2 Con­junc­tivi­tis (red­den­ing of the eyes)

�2 Nau­sea and vom­it­ing

Any­one show­ing a com­bi­na­tion of these signs and symp­toms should seek im­me­di­ate med­ical treat­ment at the near­est health fa­cil­i­ty or vis­it a doc­tor.