"In the last 40 years, the mosquito has spread to many countries," said María Guadalupe Guzmán.
Crédito: Patricia Grogg/IPS
Cuba Advancing Towards a Dengue Vaccine
Por Patricia Grogg *
In Cuba it has been demonstrated that as a dengue epidemic advances, the number of serious cases increases and changes take place in the virus genome, reports the head of a Cuban team of researchers working on a vaccine.
HAVANA, Nov 14 (Tierramérica).- "We don’t like to talk about our specific goals," says Cuban virologist María Guadalupe Guzmán, as a subtle way to avoid going into too much detail about the research she is heading up to develop a dengue vaccine.
There are a number of research projects underway around the world aimed at a vaccine against dengue, a mosquito-borne infection that causes a severe flu-like illness, and sometimes a potentially lethal complication called dengue hemorrhagic fever. Until a vaccine is discovered, however, the most important task is to control the mosquito that spreads it, Aedes aegypti, stressed Guzmán.
Although historically considered a tropical disease, dengue knows no borders today, she also emphasized. The World Health Organization (WHO) reports that the global incidence of dengue has "grown dramatically" in recent decades, and about two fifths of the world’s population are now at risk.
Guzmán works for the Pedro Kourí Institute (IPK) directing a team of 14 scientists, most of them women, in a joint project with the Center for Genetic Engineering and Biotechnology (CIGB), whose research team is headed up by Gerardo Guillén.
The major dengue epidemic that hit Cuba in 1981 defined the career path of Guzmán, head of the IPK Department of Virology and director of the PAHO (Pan American Health Organization)/WHO Collaborating Center for the Study of Dengue and its Vector.
The Cuban government maintains that the disease was introduced into the country by United States agents. Studies of the first cases to appear have made it possible to confirm that "this is not the normal pattern of a mosquito-borne disease," Guzmán told Tierramérica in this interview.
TIERRAMÉRICA: Have you been able to demonstrate that the 1981 epidemic was intentionally introduced in Cuba?
MARÍA GUADALUPE GUZMÁN: We have confirmed that the virus that was circulating here at that time was similar to the so-called old strains from Southeast Asia. It was from the years 1968 and 1944, and wasn’t circulating in Asia at the time.
In addition, a study conducted by the Ministry of Public Health revealed that the first cases of dengue appeared in three different parts of the country, in the same week, and in people who hadn’t traveled anywhere. This is not the normal pattern of a mosquito-borne disease.
TIERRAMÉRICA: What contributions has Cuba made to the studies on dengue being carried out around the world?
MGG: I would say they began with the 1981 epidemic itself. This was the first hemorrhagic dengue epidemic in the Americas, and we had to learn as we went along, because nobody had faced this problem before. It required the urgent preparation of the necessary hospital conditions and the establishment of guidelines to control the disease.
In four months, Cuba managed to bring an end to an epidemic of over 300,000 cases, including more than 10,000 severe cases and 158 fatal ones. It demonstrated the decisive role played by political will and the participation of the community and all of the sectors involved in one way or another in the problem.
Cuba contributed a great deal through this experience, from the characterization of the epidemic, to the clinical study of individual cases, especially in adults with hemorrhagic dengue – which until then had only been seen in Southeast Asia and in children – to the methods for bringing this epidemic under control in four months.
TIERRAMÉRICA: And in the field of virology?
MGG: At the time of the epidemic we were able to determine that in order for hemorrhagic dengue to occur, there must be secondary infection. We subsequently demonstrated that 20 years after contracting dengue, you are at greater risk of developing the hemorrhagic variety if you contract the disease again. You have a sword of Damocles hanging over your head for the rest of your life.
In Cuba it was also demonstrated that as an epidemic advanced and the number of cases decreased, the number of serious cases began to rise. This has happened on three occasions. The virus somehow changes over the time in which the epidemic takes place. Changes occur in the structure of the virus genome as well. This was a new observation made by Cuba.
In more recent studies we have been working on research on the genes of individuals, because your particular genetic "stock" could predispose you to certain diseases. Our group has published various studies on genes that could possibly be associated with greater susceptibility to dengue or hemorrhagic dengue.
This year a very interesting study from Vietnam was published, on the association between certain genes and hemorrhagic dengue. We also conducted a similar study, with fewer cases, published this year. The same observation was made by two different groups.
TIERRAMÉRICA: To what extent does climate change influence the transmission of dengue?
MGG: We know that the climate can have an influence, although there are few studies on the subject. We believe it is a factor, but not necessarily the only one. WHO has reported that when the temperature is one or two degrees higher, the mosquito may be able to transmit the virus in a shorter time. This is a major line of research.
TIERRAMÉRICA: There are four dengue viruses and four strains or serotypes. Is any one of them linked more than the others to hemorrhagic dengue?
MGG: Hemorrhagic dengue is a clinical classification; all of the viruses can produce it. However, within a given virus there may be different strains, and, in general, those which are isolated in Southeast Asia or other Asian countries have a greater potential to produce hemorrhagic dengue.
These viruses continue to change and transform as they spread from one person to another. As time passes, when we refer to the American-Asian genotype, these are no longer the same strains that arrived from Asia.
TIERRAMÉRICA: Do these mutations of the virus complicate the search for a vaccine?
MGG: Yes. But a lot of progress has been made in this area. There are currently six or seven vaccine candidates worldwide. The most advanced is the one being developed by Sanofi Pasteur, and according to their reports, it could be ready in seven years. It’s a live chimeric virus vaccine (obtained through recombinant DNA technology). There are other similar candidates that are also quite advanced.
Our project is a joint effort between the IPK and CIGB. It isn’t a live vaccine, but rather a recombinant subunit vaccine, which has had satisfactory results in preclinical studies with monkeys. We still haven’t moved on to studies with humans, but we also don’t like to talk about our specific goals in that regard.
* Patricia Grogg is an IPS correspondent