RIO DE JANEIRO — Brazil on Friday reported a nearly 50 percent jump in cases of dengue fever reported over a three-week period in January, a worrying finding because the disease is carried by the same mosquito that spreads the Zika virus.
“This is a very strong indication that the Zika cases are increasing and that the combat against the mosquito is not being efficient,” said Marcos Lago, an associate professor of infectious diseases and pediatrics at the State University of Rio de Janeiro.
Brazil has been panicked by thousands of suspected cases of the birth defect microcephaly, which the government has linked to an epidemic of the Zika virus that began last year.
“We will probably have a dengue epidemic,” Lago said. “And this dengue epidemic will be accompanied by a Zika epidemic.”
Brazil’s Health Ministry reported 74,000 “probable” cases of dengue from Jan. 3 to Jan. 23 — an increase of almost 50 percent from the same period in January 2015.
Dengue, Zika and another disease called chikungunya are spread by the same mosquito — the Aedes aegypti. The government is urgently trying to slow the increase in the number of such mosquitoes, which lay their eggs in standing water.
President Dilma Rousseff and government ministers plan to join 220,000 Brazilian soldiers who will visit homes Saturday to educate the population about the mosquito.
Next week, 50,000 members of the military will visit homes to try to eradicate breeding spots.
Rousseff and Health Minister Marcelo Castro have cautioned that Brazil is losing the battle against the mosquito.
The government has blamed Zika for a big rise in the number of babies born with microcephaly, a congenital defect that is characterized by an abnormally small head. The malformation can cause motor and learning difficulties along with other disabilities.
The U.S. Centers for Disease Control and Prevention and the World Health Organization have yet to definitively establish a link between Zika and microcephaly, but many leading scientists think a connection is likely.
Dengue, a severe flu-like illness, has been in Brazil for decades.
Zika was first confirmed in Brazil in May 2015 and has rapidly spread across the Americas.
If mosquitoes are spreading dengue, they could be spreading more cases of Zika and chikungunya as well, doctors warn.
“If it is transmitting dengue, it can transmit all the others,” said Jessé Alves, a specialist in infectious diseases at the government’s Emilio Ribas Hospital in Sao Paulo.
The number of probable cases of dengue rose from about 600,000 in 2014 to 1.6 million in 2015, according to official statistics. The government estimates that as many as 1.5 million people may have caught Zika. In 2015, Brazil recorded nearly 21,000 cases of chikungunya, which, like dengue, is marked by fever and joint pains.
“If there is a spike of all three of them, it could mean the mosquito is becoming more efficient,” said Anandasankar Ray, associate professor of entomology and the director of the Center for Disease Vector Research at the University of California at Riverside.
The mosquitoes are attracted to the smell of humans, biting in the day and at night.
Dengue has spread dramatically around the globe in recent decades, according to the WHO. The number of reported cases in the Americas, Southeast Asia and the Western Pacific grew from 1.2 million in 2008 to more than 3 million in 2013, according to the agency.