Preventing dengue
OVER the years, the mosquito-borne viral infection dengue has assumed the dimension of a global public health crisis — WHO estimates over 2.5 billion (40 per cent) of the world’s population is at risk. In Pakistan, dengue is now a major public health challenge.
Pakistan’s first registered case of dengue occurred in Karachi in 1994, when one death was reported. Since then, various studies have reported dengue spreading to various parts of the country. In 1996, 57 cases were reported in Hub, Balochistan. In 2003, 717 cases were reported in Haripur (KP) and Khushab (Punjab), of which six proved fatal. In 2005 and 2006, Karachi again saw a dengue fever epidemic with 103 and 4,759 cases reported, and six and 50 lives lost respectively. In 2009 and 2011, Lahore witnessed the most severe outbreaks of dengue yet. The latter epidemic claimed some 300 lives.
One research paper on the 2011 epidemic showed that the spread of dengue fever was the result of a combination of burgeoning slums and urbanisation, and a lack of coordination at tertiary levels, health facilities, health education and prevention strategies. The study also found that ownership by political leadership contributed to improved preparedness and an effective response as evidenced the following year, when the number of cases was drastically reduced and no fatalities reported. Sri Lankan expertise in dengue control was usefully tapped. The Sri Lankan example shows how a robust strategy can help in the prevention and control of the disease.
Dengue spreads when a female Aedes aegypti (or yellow fever) mosquito bites an infected person and transmits the disease to a non-infected person; this period of transmission is spread over about 10 days. The mosquito breeds in dark places, water containers and other areas. Fever is the most common manifestation of dengue, along with body aches and headaches. In extreme cases, the disease develops into dengue haemorrhagic fever, which can be fatal. One study found that more males are affected than females, and it usually affects ages 20 to 39 years. Dengue fever is usually rampant during the monsoon and from September to December.
There are many strategies that can be explored.
While Pakistan has made considerable progress in controlling and containing dengue fever in recent years, there is still a lot we can learn by employing new techniques and methods to prevent and control dengue in the country.
Globally, dengue is being controlled through various strategies. Control strategies involve chemical, physical and biological methods. In physical control methods, GIS mapping is employed to pinpoint dengue concentration areas. This allows for effective control strategies to be devised and implemented. A focused and effective dengue surveillance system is a must if we are to provide information on the outbreak — on its distribution and extent.
Community-based control programmes, meanwhile, are geared towards educating people about mosquito breeding sites and instituting appropriate preventive measures. There has been considerable focus on this aspect of late. Nowadays, a dengue alert leads to a flurry of health information and preventive activity. Lady Health Workers visit homes to spread awareness about transmission routes, the spread of the disease and adopting preventive measures at the household level. Posters go up at key places in dengue-prone regions. Singapore has made great strides in dengue control by instituting a community alert system that detects foci of dengue concentration, which are then colour coded.
Chemical strategies concentrate on traditional methods including the use of insecticide spray to eliminate mosquitoes and control dengue. Biological strategies focus on releasing genetically modified mosquitoes into the vector population, which disturbs the sexual cycle of the female mosquitoes leading to a reduction in the mosquito population. Another strategy is the sterile insect technique. This has shown considerable promise. It consists of releasing genetically sterile male mosquitoes into the vector population. This reduces the fecundity rate of female mosquitoes thus contributing to a reduced mosquito population and less dengue transmission.
Another method of control is based on immunotherapies and vaccines. In recent years, the development of a live, attenuated vaccine has been shown to protect against the virus in Mexico. However, while some methods show promise, some new vaccines have been withdrawn out of safety concerns. In the Philippines, the government is investigating the deaths of two children whose parents suspect a newly trialled vaccine was responsible. Safety concerns have led the government to ban the vaccine.
While the race is on to find a safe, effective vaccine, this region offers a potential breakthrough in dengue control. Pakistan has gone some way down the road to do so, yet there is a raft of strategies in development that, if employed, can be helpful in controlling the transmission of dengue.
The writer is a public health and development consultant.
Published in Dawn, January 21st, 2018