Amid concerns that the zika virus may be transmitted through infected semen, new findings suggest that a potential vaccine, which works by ring-fencing the virus and appears to protect the testes from infection, in mice, may be on the anvil.
Though historically known as a virus causing no more than a mild fever and rash, the 2015 epidemic caused a global scare as it was linked with microcephaly, a congenital anomaly resulting in an abnormally small brain in newborns of zika-infected mothers.
Damaging effects
Passing on the virus to a pregnant woman through sex or impregnation with infected semen is a major concern vis-à-vis microcephaly, says Karuppiah Muthumani, from Madurai, who is now a member of the Vaccine Centre at the Wistar Institute in Philadelphia, U.S., an international leader in biomedical research with special expertise in cancer research and vaccine development. Dr. Muthumani is at the centre of an international collaboration that produced a vaccine, the first to be approved for clinical trials by the U.S., and now undergoing human trials in the U.S., Canada and Puerto Rico. All documented cases of sexual transmission, over 40 in the U.S. alone, are reported to have originated from men.
Efforts to protect the male reproductive organ and, by extension, preserving fertility, is not just aimed at infection control, Dr. Muthumani says. One of the most definitive demonstrations of zika’s damaging effects on the testes was made last year in the journal Nature .
The publication by Jennifer Govero of Washington School of Medicine and others, showed extensive damage to the organ, epididymis and a subsequent reduction in testosterone levels.
“During our pre-clinical assessment, vaccinated mice were able to conserve their testes as they had no viral RNA in the organ following exposure to zika,” he says. The team found that testicular size, weight, sperm count and motility remained conserved in vaccinated mice.
More significantly, initial experiments have shown that serum from immunised animals, when transferred to unvaccinated mice infected with zika, helped in restricting testicular damage. The efficacy and prospects of immunised sera in treating zika, which could lead to therapies for post-exposure prophylaxis, were already shown in the team’s first paper describing the vaccine in the November edition of the journal, NPJ Vaccines .
While the World Health Organisation deemed the outbreak to be over last November, it still sends out advisories on the need to refrain from non-essential travel to zika-affected areas if pregnant or contemplating pregnancy, and, in case of men, to abstain from sex or avoid unprotected intercourse for six months after return from an area with zika. These precautions were affirmed by a February 14 study published in the New England Journal of Medicine , which found that zika RNA can persist for as long as 125 days, after onset of symptoms.
Vigilance in India
Zika is said to be endemic in India, with many believed to be buffered by antibodies against the virus. However, given that the zika-carrying Aedes mosquitoes are widely spread in India, Bangladesh, Pakistan, the Indian government has surveillance-programmes in place for the virus, apprehending infections due to the vector’s presence. Dr. Soumya Swaminathan, Director General of the Indian Council of Medical Research (ICMR) says those efforts have now become part of the country’s regular vigilance exercise.
“The number of labs that can test for zika has consistently grown to 35. We have also tied-up with Monash University in Australia to bring in an innovative vector control method,” she says.
Interestingly, India’s own efforts at vaccine development were announced before that of others at the peak of the outbreak last year. ICMR is collaborating with the vaccine maker and efforts are under way to test the vaccine in clinical trials later this year, adds Dr. Swaminathan.
