An outbreak of mosquito-borne dengue fever [1] has infected at least 55,000 people in Brazil’s state of Rio de Janeiro, killing 67 people as of Tuesday, according to CNN.com [2].

Historically prevalent in Latin America, incidences of the viral disease subsided in the mid- to late-20th century due to widespread mosquito extermination efforts, according to the Washington Post. [3]

Dengue infected between 630,000 and 900,000 people in the region during 2007, depending on estimates, as many as half of them in Brazil, and 25,000 in Rio.

The current outbreak is blamed on urbanization, especially the growth of shanty towns in Rio, and a lack of public education on the danger posed by standing water, according to a U.S. official quoted in the Post:

Wellington Sun, chief of the dengue branch [4] for the U.S. Centers for Disease Control and Prevention [5], said the demographic shifts that turned Latin America from mostly rural to predominantly urban in recent decades have given the dengue-carrying mosquito a perfect environment in which to thrive. The mosquito needs only a tiny amount of standing water to breed -- even a piece of crumpled plastic garbage is enough, Sun said. Eliminating breeding pools is very difficult in areas where trash collection is infrequent and water and sewer services are lax.

Meanwhile, residents and some government officials blame authorities for failing to address the outbreak sooner. It took a judge’s order on March 29 to compel [6] public hospitals to send poor victims, waiting up to 28 hours in line outside overwhelmed facilities, on to private hospitals. This week, the Brazilian military established field hospitals to provide relief.

Dengue has multiple forms, the hemorrhagic being the most deadly.  While infection with many common diseases creates immunity, experts believe [7]that prior infection with a mild form of dengue leaves the patient more susceptible to the hemorrhagic form.

There is neither a vaccine nor cure for dengue, only treatment with fluids, either orally or intravenously.