Babies exposed to Zika virus before birth can go on to develop microcephaly and other complications after they are born, according to a study today from Brazil.
In other research news, Chinese scientists who did experiments in mice found more evidence that the virus may damage the male reproductive system.
Late-developing microcephaly
Clinicians in Brazil have reported a few cases of delayed-onset Zika-related microcephaly in babies born with normal head size, as well as neurologic complications in newborns without obvious deformities. However, today's study based on babies from two Brazilian states, is the largest series so far and provides a clearer picture about what scientists have said is a clinical syndrome rather than only microcephaly.
Researchers from Brazil, the United States—including from the US Centers for Disease Control and Prevention (CDC)—reported their findings today in an early edition of Morbidity and Mortality Weekly Report (MMWR).
The 13 babies described in the report didn't have microcephaly at birth, but were later found to have slow head growth. Of that group, 11 developed microcephaly. Detailed neurologic imaging and clinical follow-up showed that all of them had significant brain abnormalities consistent with congenital Zika syndrome. Sixty percent had epilepsy, and all had significant motor disabilities.
Though many of the physical findings were similar to those of babies born with microcephaly, infants with the late-developing condition were more likely to make and hold eye contact and smile, showing better social interaction.
Of the six mothers who reported a rash during pregnancy, four had the symptom during the first trimester and two reported it during the second trimester. The researchers said the finding suggests that early infection during pregnancy doesn't always lead to the most severe outcome: microcephaly at birth.
The mechanism behind late-developing microcephaly isn't yet known, but it might be linked to earlier destruction of brain cells, persistent inflammation, or lingering infection in neural cells. The team, however, said persistent virus seems less likely, given that all seven tested cerebrospinal fluid samples were negative for Zika virus.
Evidence for male reproductive system damage
Echoing similar findings by a US team a few weeks ago, Chinese researchers yesterday reported evidence of damage to the male reproductive system from Zika virus, based on experiments in mice. They published their findings in the latest issue of Cell.
After infecting male mice with Zika virus and analyzing the effect on the urogenital tract, they found evidence of the type of Zika-related damage after 60 days that could impair fertility. For comparison, they also injected another group of mice with dengue virus and also looked for signs of damage.
Zika virus can trigger inflammation in the testis and epididymis, but not the prostate or seminal vesicles, according to the report. All of the Zika-infected mice developed acute testicular inflammation, compared with 10% of the dengue-exposed group.
The researchers identified two types of cells that seemed to be especially vulnerable to the virus, and they observed signs of testicular structural damage that appeared to be permanent in mice infected with Zika virus, but not in those infected with dengue virus.
They urged more studies and clinical follow-up in men who have Zika virus infections.
See also:
Nov 22 MMWR early release report
Nov 22 CDC press release on the study
Nov 21 Cell abstract
Oct 31 CIDRAP News story "Study hints at Zika fertility problems in men"
