An outbreak of chikungunya virus affected over one-third of the population of La Réunion Island between March 2005 and December 2006. In June 2005, we identified the first case of mother-to-child chikungunya virus transmission at the Groupe Hospitalier Sud-Réunion level-3 maternity department. The goal of this prospective study was to characterize the epidemiological, clinical, biological, and radiological features and outcomes of all the cases of vertically transmitted chikungunya infections recorded at our institution during this outbreak.
Methods and Findings
Over 22 mo, 7,504 women delivered 7,629 viable neonates; 678 (9.0%) of these parturient women were infected (positive RT-PCR or IgM serology) during antepartum, and 61 (0.8%) in pre- or intrapartum. With the exception of three early fetal deaths, vertical transmission was exclusively observed in near-term deliveries (median duration of gestation: 38 wk, range 35–40 wk) in the context of intrapartum viremia (19 cases of vertical transmission out of 39 women with intrapartum viremia, prevalence rate 0.25%, vertical transmission rate 48.7%). Cesarean section had no protective effect on transmission. All infected neonates were asymptomatic at birth, and median onset of neonatal disease was 4 d (range 3–7 d). Pain, prostration, and fever were present in 100% of cases and thrombocytopenia in 89%. Severe illness was observed in ten cases (52.6%) and mainly consisted of encephalopathy (n = 9; 90%). These nine children had pathologic MRI findings (brain swelling, n = 9; cerebral hemorrhages, n = 2), and four evolved towards persistent disabilities.
Mother-to-child chikungunya virus transmission is frequent in the context of intrapartum maternal viremia, and often leads to severe neonatal infection. Chikungunya represents a substantial risk for neonates born to viremic parturients that should be taken into account by clinicians and public health authorities in the event of a chikungunya outbreak.
In a prospective study on the island of La Réunion, Marc Lecuit and colleagues find frequent transmission of Chikungunya virus by viremic mothers giving birth during an outbreak, resulting in serious infant illness.
Chikungunya virus, an emerging infectious agent that is transmitted by day-biting mosquitoes, was first isolated from a patient in Tanzania in the early 1950s. Since then, major outbreaks of chikungunya fever have occurred throughout sub-Saharan Africa and in Southeast Asia, India, and the Western Pacific, usually at intervals of about 7–8 years. The virus causes fever, rash, severe joint and muscle pains, and sometimes arthritis (joint inflammation). These symptoms develop within 3–7 days of being bitten by an infected mosquito. Most people recover fully within a few weeks, but joint pain can sometimes continue for years. There is no treatment for chikungunya fever, but the symptoms can be eased with anti-inflammatory drugs. Preventative measures include covering arms and legs and using insecticides to avoid insect bites and depriving the mosquitoes of their breeding sites by draining standing water from man-made containers near human dwellings.
Why Was This Study Done?
In 2005, chikungunya fever appeared for the first time on several islands in the Indian Ocean. On La Réunion Island, the disease affected 300,000 people—more than one-third of the population—between March 2005 and December 2006. In June 2005, clinicians identified the first case of mother-to-child chikungunya virus transmission (vertical transmission). Public-health officials and clinicians need to know more about how often vertical transmission occurs and its clinical implications to help them prepare for future chikungunya fever outbreaks. In this study, the researchers identify and characterize all the cases of vertical chikungunya virus transmission that occurred at the largest hospital on La Réunion Island during the 2005–6 outbreak.
What Did the Researchers Do and Find?
The researchers enrolled all 7,504 women who gave birth at the hospital during the outbreak and their 7,629 children into their study. They then used “RT-PCR” (which detects the genome of virus particles during an active infection) and “IgM serology” (which looks for an immune response to recent infection) to determine which women had been infected with chikungunya virus during their pregnancy. 678 of the new mothers had been infected sometime between conception and a week before delivery, 22 mothers had been infected between 7 and 3 days before delivery, and 39 had been infected 2 days either side of delivery (the “intrapartum” period). Except for three early fetal deaths that were associated with chikungunya virus infections, vertical transmission was seen only in babies born to mothers infected with the virus intrapartum. 19 of the babies born to these women were infected with the virus—a vertical transmission rate of nearly 50%. The women who transmitted the virus to their offspring had more virus in their placenta than those who did not transmit the infection. Delivery by emergency cesarean section did not prevent transmission. All the infected babies were born healthy but developed fever, weakness, and pain within 3–7 days. In many of them, the number of platelets (clot-forming particles) in their blood also dropped dramatically. Ten babies became seriously ill—nine of them developed brain swelling; two had bleeding into their brain. Four children had lasting disabilities at the end of the study.
What Do These Findings Mean?
These findings show that mother-to-child transmission of chikungunya virus occurs frequently when women are infected with the virus at the time of delivery and that newborn children infected by this route can become very ill. Although these results do not find that cesarean section reduces infection rates, 90% of cesarean sections involving infected infants were performed urgently, rather than planned. The study also provides no information about whether delaying delivery, provided that no fetal distress is observed, until the mother's viral load has decreased might be beneficial. More studies are needed to provide a complete description of both the short-term and long-term effects of chikungunya virus infection in newborn babies, but it is clear that clinicians should monitor babies exposed to chikungunya virus during delivery for a week after their birth. Most importantly, clinicians and public-health officials will need to take account of the threat that the chikungunya virus poses to newborn children whenever and wherever it emerges.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0050060.
Read the related PLoS Medicine 10.1371/journal.pmed.0050068
The World Health Organization provides information about chikungunya fever and a brief description of the recent chikungunya outbreak in the Indian Ocean (in English, French, Spanish, Arabic, Chinese, and Russian)
The US Centers for Disease Control and Prevention has a fact sheet on chikungunya fever
The UK Health Protection Agency also provides information about chikungunya virus, including news on recent outbreaks
The French Institut de Veille Sanitaire (Institute for Public Health Surveillance) has a Web page on chikungunya (in French)
The Institut Pasteur has a Web page on chikungunya research (in French and English)