A dengue epidemic is raging in Central America, from Honduras to Costa Rica. The virus has already claimed 60 lives, with a total of 120,000 cases. The Pan American Health Organisation fears the figures may "explode", with this year looking "unusually bad".

Several factors are likely to exacerbate the situation. The rainy season, which starts in June in that part of the world, is set to continue until November. With heavy rainfall and torrid heat, conditions are particularly favourable for proliferation of the main vector of dengue fever, the Aedes aegypti mosquito, whose eggs hatch on the surface of ponds.

With the rising number of new cases, Honduras, El Salvador and Costa Rica announced a health emergency in July and launched campaigns to prevent the disease from spreading. Lacking adequate resources, Honduras, which has been hardest hit with at least 17 fatalities and 20,000 cases reported, appealed to the International Red Cross for help.

"The $169,000 in aid provided by the disaster relief emergency fund enables us to distribute mosquito nets in high-risk areas, promote hygiene and combat vectors, in order to halt mosquito reproduction," says Amanda McClelland, a Red Cross co-ordinator.

The poor suburbs of Central American capitals are the main targets for campaigns to raise public awareness. Poor housing, the lack of a mains water supply and the accumulation of household waste make such neighbourhoods an ideal breeding ground for mosquitoes. The authorities have dispatched paramedics, police and the military to remote villages in order to stamp out the epidemic in the areas most at risk.

Latin America is particularly exposed to dengue epidemics, which recur on a three- to five-year cycle. In 2010 the fever caused 132 deaths. "Aedes aegypti was eradicated in the subcontinent in the mid-20th century, but with increasing global trade it returned in the 1970s, from Asia," says Philippe Brémond, an epidemiologist at France's Institute of Research for Development (IRD).

In 2010 the World Health Organisation reported 1.6 million cases of dengue fever in Latin America, of which 49,000 were severe, a leading cause of death among children in the region. The Philippines is also in the grip of a dengue epidemic, which has claimed 10 lives. The virus leads to fever with headaches, and painful muscles and joints. In its severe form it can cause potentially fatal internal bleeding.

"It has been difficult to eradicate dengue because there are four different strains, which operate like four completely distinct viruses," Brémond explains. "This feature makes it much easier for the disease to circulate than for others. Once cured a patient is immune for life to the strain that caused the infection, but not the three others."

Brémond expects the epidemics to continue in Latin America until "herd immunity" is achieved there, with a sufficient number of people immunised to stamp out the virus. This long process may be speeded up by a vaccine currently being developed by France's Sanofi Pasteur.

Much is at stake. The WHO estimates that between 50 and 100 million people are infected worldwide annually, mainly in the tropics. A study by researchers at Oxford University suggests that the number of new infections every year is closer to 390m.

First four-in-one vaccine on way

The first four-in-one dengue vaccine, developed by France's Sanofi Pasteur, is due to start production later this year at Neuville sur Saône, just north of Lyon, coming on to the market in 2015. "We have reached a very important stage, entering phase three of clinical trials, and in the course of 2014 we expect to see the efficacy data from trials on 30,000 volunteers in 10 countries in Asia and Latin America," project leader Guillaume Leroy said in July.

Management at the parent company Sanofi is presenting the drug as a "strategic" business venture, the potential market being worth an estimated $1bn.

As it takes two years to manufacture a vaccine, the firm has decided to launch the process before receiving the necessary marketing authorisations, following clinical trials.

This article appeared in Guardian Weekly, which incorporates material from Le Monde