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.