The Zika virus is rampant in Latin America. It is an infection that can cause deadly birth defects in fetuses. Health authorities in Rio are taking drastic steps to prevent the virus from spreading during Carnival.
Some 30 employees from the Rio de Janeiro health authority have arrived at the parade avenue of the city's Sambadrome to spray nearly 900 meters (1,000 yards) of track, as well as all of the bleachers surrounding it, with insecticide. In just a few days, Carnival will begin in Rio. When it starts, 70,000 people will fill the Sambadrome for four consecutive nights to cheer the Samba groups that perform there until the morning hours. In August, archery events are scheduled to take place here when Brazil hosts the 2016 Summer Olympics.
But anticipation of the events has been dampened because the numbers of those contracting the Zika tropical infection in Brazil have been rising so rapidly. "There is grave concern throughout Rio," says Marcus Vinicius Ferreira, spokesman for the city's health authority. "Tourism numbers increase greatly during Carnival, and that could foster the spread of the virus."
So far, 22 American countries have reported cases of Zika infection. The first case in the USA was diagnosed at the start of the week. Areas that are warm and damp are considered to be at risk of an epidemic, because the virus - like many tropical fevers - is spread by mosquitos. The "Aedes aegpti," better known as the yellow fever mosquito, also spreads dengue and yellow fever, as well as chikungunya.
Difficult to control
Compared with the "breakbone fever" dengue, the Zika infection's disease progression is often harmless. Although the symptoms of fever, head, muscle and joint ache, as well as rashes, are the same as those of dengue, they are generally much less intense. Serious cases of illness may - as with most febrile illnesses - end in death, however, that happens very rarely. Some 80 percent of those infected suffer no symptoms whatsoever.
That is exactly what makes the disease so difficult to control. Those infected become unwitting vectors, and can pass on the Zika virus to other humans without knowing it - for instance through blood transfusion or sexual intercourse.
Fetuses at risk
That would hardly be reason enough for Brazil's health minister to call in the military. But the virus apparently triggers microcephaly - abnormal smallness of the head - in fetuses when it infects pregnant women. This can lead to mild mental impairment, serious disability and even the death of the child.
"So far it has not been proven that the Zika virus actually triggers microcephaly," explains human biologist Lavinia Schüler-Faccini from the University of Health Sciences of Porto Alegre. "But the recorded correlations between the occurrence of the virus and deformities leave no room for doubt."
The virus was discovered in the Zika Forest in Uganda in 1947. It was recorded for the first time in Brazil in April 2015. Since then, the number of infections has skyrocketed. The Brazilian Ministry of Health estimates that there could be upwards of 600,000 infections this year.
Cases of microcephaly in Brazil have increased parallel to the spread of the virus. Since October 2015, 3,800 cases have been recorded - 40 times more than normal for a comparable timeframe.
The US government has therefore warned pregnant women against traveling to 14 Latin American countries. Local Latin American authorities have advised women to delay wanted pregnancies. Columbia's Ministry of Health suggests waiting until July - when they hope to have a clearer picture of the situation. In El Salvador, authorities advise waiting until 2018.
Infections are increasing
So far, Brazil is the only country to deploy its military to fight the disease, or more accurately, to fight the Aedes mosquito. Soldiers have been tasked with informing the population and distributing mosquito repellant.
Scientist Schüler-Faccini finds the move appropriate: "Of course the military is not trained to fight mosquitos, but the situation calls for a rapid response." One reason is that the Aedes mosquito appears to reproduce very quickly. That assumption is suggested by the dramatic rise in cases of dengue fever infection in 2015 - the number of those infected went up 178 percent compared to 2014.
Schüler-Faccini is advising the Brazilian Ministry of Health in the fight against pregnancy risks. She reports on epidemiological threats in a weekly newsletter. Pregnant women in welfare programs are now supposed to receive mosquito repellant.
Rio not a flashpoint
The state of Pernambuco in northeastern Brazil has been the hardest hit by the Zika virus. In Rio's City Hall, officials point to regular prevention measures as the reason that there has not been an epidemic of tropical fever in the city. That is also why Marcus Vinicius Ferreira from the Rio de Janeiro health authority says: "We don't need the soldiers. We can deal with this on our own." More than 3,000 city employees and a further 7,000 helpers are already in action in the city's poor neighborhoods.
Citizens' help in the fight against the mosquitos is of the essence, as some 80 percent of nesting places are directly situated around apartments. The Aedes mosquito can lay its eggs anywhere that small amounts of standing water can be found.