Dengue Fever is a viral illness that comes from a mosquito bite. The chief concern facing health officials is that the cases that are facing doctors are getting more severe and that people are coming down with the illness a second time.
Those who fall ill a second time are at a greater risk.
The total number of cases has fallen in the Americas to 5.5 percent. In 2007 there were 850,769 cases, mostly in Bolivia and Brazil.
During this same period more severe cases jumped 46 percent and death counts leaped 84 percent from 317 to 584.
The trend for more severe cases has continued into 2009. From January to early April the Pan-American Health Organisation (PAHO) has reported more than 215,000 cases in the Americas. Argentina has had many of the new cases. There is also a new rise in deaths, from 1.2 percent of those infected in 2007 to 2.2 percent so far in 2009.
While in the past it was thought that once a person had dengue fever they were immune the fact is they are only immune to the strain they came down with. Doctors are finding that those who have had one strain are more vulnerable to the other strains.
Most cases of dengue fever go undiagnosed because the symptoms are similar to the flu virus. Symptoms include fever, headache, and muscle and joint pain. In more severe cases patients have slight haemorrhaging, a rash or bleeding gums. the most severe cases of dengue hemorrhagic fever (DHF) and dengue shock syndrome appear to be more frequent with those who are suffering a second infection.
In Brazil the Ministry of Health has reported that in the first 10 weeks of the year there have been 114,355 cases, of which 603 were severe and 23 ended in death.
Although PAHO underscores that studies demonstrate that sequential infection heightens the risk of DHF, infectious disease expert Dr. Rogério Valls de Souza of Fiocruz says "there is no definitive data" about how many people are vulnerable to a severe case of dengue because they already had the disease.
"Dengue is related to the type of virus that is circulating. For example, in the Rio de Janeiro epidemic - in the 2008 southern hemisphere summer - the virus that circulated most was type 3, and the most serious cases, not necessarily hemorrhagic, were manifest in the first infection," he noted in a Tierramérica interview.
It is being noted by doctors dealing with the crisis that once a person is reinfected with the illness they face a higher likelihood of developing the hemorrhagic type of the virus.
"In the Americas we have four strains of dengue. Once a person has fallen ill, the next time, no matter how much time has passed, if he or she is infected by another strain there is a full chance of developing the hemorrhagic type," Dr. Jorge Gorodner told Tierramérica. Mortality in that case is 15 to 35 percent, he said.
"Almost 100 percent of the infected are susceptible (to DHF). But the severity of the disease depends on each person," said Gorodner, complaining that the lack of epidemiological oversight means the epidemic causes even more harm.
Because of the four separate strains of the illness a safe vaccine is not a viable tool at this time. Partial immunity could prove even more dangerous as if a person does become infected the partial immunity would put them at greater risk for a more severe case.