Zika Virus Outbreak in Dhaka, Bangladesh, September–December 2024

Summary

• Zika virus spreads mainly through bites of infected Aedes mosquitoes. Most infections are mild or silent, but it can rarely cause serious nerve complications, and infection in early pregnancy can cause severe birth defects.
• In Bangladesh, Zika was first found in a stored sample from 2014; five cases were identified in 2023.
• In September–December 2024, 10 confirmed cases were found in and around Dhaka, the capital, in people who hadn't traveled abroad. Most were first thought to have dengue or chikungunya. None was pregnant or hospitalized, and Zika virus was found in local mosquitoes.

Background

Zika, first identified in Uganda in 1947, caused its first documented outbreak on the Pacific island of Yap in 2007, and a large outbreak in Brazil in 2015–2016 revealed its link to microcephaly in babies infected before birth. Besides mosquito bites, it can pass from mother to baby in the womb or at birth, sexually, through breastfeeding, blood transfusion, laboratory exposure and organ or tissue transplants. Infection in early pregnancy can cause congenital Zika syndrome — microcephaly, brain abnormalities, vision problems, low birth weight and other conditions.

In Bangladesh, testing of stored dengue-negative samples from 2013–2016 found one Zika-positive specimen from 2014, and a 2023 study by a nongovernmental research group in Dhaka found five Zika cases among 152 feverish patients. Zika is a notifiable disease there, but there's no routine surveillance for it.

How the outbreak was found

• The first case: on September 4, 2024, a 29-year-old woman in Dhaka, not pregnant, with fever, joint pain and rash since August 31, tested positive at a hospital outpatient department. Doctors, after a negative rapid dengue test, had ordered a multiplex test for dengue, chikungunya and Zika, suspecting chikungunya; it found only Zika. The national Institute of Epidemiology, Disease Control and Research (IEDCR) confirmed it in serum and urine. Her five household members all tested negative.
• An outbreak declared: in Bangladesh, even one confirmed case with suspected local spread counts as an outbreak, and IEDCR declared one on September 9. It alerted hospitals, the public (through a media briefing) and the country's obstetrics and gynecology society, and told all government hospitals to refer suspected Zika, chikungunya or dengue patients for testing.
• Hospital cases: on September 17, a second hospital reported two cases, both first suspected as dengue; a visit to one patient's home found a household member who was also infected. Two more hospitals reported cases on October 5 and October 20.
• Hidden among chikungunya: during a chikungunya outbreak in October, IEDCR set up a sample collection booth for referred patients. Of 394 tested in October–December, 34 (8.6%) met the suspected-Zika definition, and four were confirmed — three by urine and one by serum. Overall, 138 had chikungunya, 11 dengue and four Zika.

The patients

Sexual contact, transfusion and transplants were ruled out, none had traveled abroad in the 2 weeks before falling ill, and only two cases appeared linked. No one had dengue or chikungunya as well.

Mosquitoes: larvae were collected from ponds or lakes at seven sites, each within about 0.5 miles (1 km) of a patient's home, raised to adults and tested. One site's pooled sample carried Zika virus RNA.

Zika cases (red) and the mosquito-positive site (blue), Dhaka, 2024. Figure from the CDC report.

The response

• IEDCR's Public Health Emergency Operations Center sent teams to investigate every reported case, and awareness was raised online among clinicians and the public.
• Zika screening was added to chikungunya testing, and has continued through the 2025 dengue and chikungunya season (June–December); fever surveillance began at six sites nationwide, and a serosurvey in Dhaka is gauging how widespread Zika and related viruses are.
• City mosquito control for dengue continues, and pregnant patients with Zika-like, dengue-like or chikungunya-like illness are to be referred for testing.
• Provisional data show fewer than 10 confirmed Zika cases in Bangladesh in June–November 2025.

What it means

• Zika is circulating in Dhaka. This was the city's first outbreak of this size and the second year running with cases, raising the chance the virus becomes endemic. Unlike 2023, when all five patients lived within about 0.5 miles (1 km) of each other, the 2024 cases were spread out — pointing to established circulation in mosquitoes.
• The true toll is likely higher, given no systematic surveillance, limited testing, mild or silent infections, and misdiagnosis as dengue or chikungunya.
• Build on dengue surveillance: Bangladesh's national dengue system could be widened to cover Zika and chikungunya together.
• Test and protect: doctors should consider Zika testing for feverish patients suspected of dengue or chikungunya — especially pregnant women with fever or rash, who may need monitoring during pregnancy — and communities should be urged to prevent mosquito bites, alongside stronger mosquito control.

Sources

Based on Jannatul Ferdous, Md Abdullah Omar Nasif, Gretchen Cowman and others (Institute of Epidemiology, Disease Control and Research, Bangladesh, and CDC), "Zika Virus Outbreak — Bangladesh, September–December 2024," MMWR, Centers for Disease Control and Prevention; published by CDC and in the public domain; rewritten in hubnx's own words. The source's "Flavivirideae" and "IECDR" are corrected to Flaviviridae and IEDCR, and the figure's source description, which belonged to another report, is replaced.