Zika viruses have been found in tears, possibly explaining why some patients have suffered from conjunctivitis and, in rare cases, permanent vision loss.
An Aedes aegypti mosquito, which spreads the Zika virus. Credit: riyagi/Flickr, CC BY 2.0
British Virgin Islands and Singapore are the newest territories to report spread of mosquito-borne Zika infection. This brings the worldwide figures up to 72 countries and territories since 2007, as of the WHO’s statistics from September 1. Of these, 20 have reported cases of Zika-associated central nervous system malformations like microcephaly.
According to a September 6 report from Singapore-based TV channel Channel News Asia, the number of confirmed cases in the country has hit 275 in less than a couple weeks, 15 of those Indian nationals. The government has launched vector control and outreach programmes to tackle the situation in susceptible areas.
The progress of the disease in Singapore has raised alarm bells in other Asian countries which being similarly humid, densely populated make perfect breeding grounds for mosquitoes. Indonesia, Thailand, Malaysia, the Philippines and Vietnam have already reported Zika cases. A study published last week in The Lancet analysing the spread of the epidemic identified Africa and the Asia-Pacific as regions that are at highest risk for infection. 2.6 billion people live in these regions, resident Indians alone comprising 1.2 billion of this.
Medal for the Olympics and an Indian Scare
The Brazil Olympics concluded with no confirmed cases of Zika among the attendees. A WHO committee that convened on September 1 lauded the organisers for their effective implementation of public health measures. The stage is now set for the Paralympic Games, due to begin this week in Rio.
India had a brief scare when its steeplechase participant Sudha Singh returned from Brazil ill and had to be tested for a number of infections including Zika. Her tests came out negative for Zika and positive H1N1 virus. The athlete was treated and has since been discharged from the hospital.
The same WHO committee agreed that it was prudent to uphold Zika’s status as a public health emergency in light of its continuing spread and growing understanding of the virus and its associated neurological disorders.
Meanwhile, the virus continues to spread sexually, prompting WHO to update its guidelines on the matter. Because of the apparent risk Zika poses to pregnant women, it advises both men and women who have been in Zika-affected areas to practice safe sex for at least six months. The advised period used to be eight weeks but, since it emerged that even asymptomatic persons could transmit the virus, it was extended to six months.
More about the virus
Research on the Zika virus, its transmission, effects and management have continued to trickle in. An international team of researchers published the sequence of a strain of Zika virus that will henceforth be used as the reference sequence to identify the virus and diagnose infection, announced WHO. The strain was isolated from a French Polynesian patient in 2013 and was chosen for its similarity to currently circulating viruses making it an adequate representative of viruses that are clinically significant and have widespread distribution. The formal review of this sequence by WHO will take place only in October but the agency has said since the need is urgent, there’s no need to wait until them for this sequence to be used.
American scientists compared the virus’s Asian and African strains and found that there were some differences in the way each infects neural progenitor cells. The current outbreak, which has made news for its neurological effects like congenital microcephaly and Guillain-Barré syndrome is more closely linked to the Asian strain so understanding such differences is important.
Some fortunate news for vaccine development from another American study. It appears that despite genetic differences between the two strains, a vaccine developed against one strain of the virus will act against the other strain as well. This is because all Zika strains seem to have identical surface antigens – the proteins on an invading cell or particle that attracts specific antibodies in the host. This is in contrast to dengue infection where strains differ in the type of surface antigens on them. That means immunity against one strain does not mean that an individual is resistant to other strains.
Discoveries on transmission
A research study published in August showed that female Aedes aegypti mosquitoes are able to transmit Zika to their eggs and offspring. This has implications for mosquito control because it means that techniques like spraying which affects only adults, may not be sufficient.
Scientists studying the West Nile virus’s spread among birds found that those with higher levels of the stress hormone corticosterone are more likely to be bitten by mosquitoes carrying the virus. Their results may be significant to understand what makes a host attractive to mosquitoes carrying other viruses like Zika.
For the first time, scientists were able to create a mouse model of a Zika infection transmitted via the vagina. Though it was known that Zika can be transmitted sexually, this is one of the first evidence that that viruses from a vaginal infection are capable of infecting the unborn foetus’s brain. The researchers called this discovery “worrisome” as it suggests that vaginal secretions, like semen, is a potential reservoir for Zika virus replication in humans.
A couple of new suspected Zika-linked disorders have reared their heads – sensory poly neuropathy, a disease of the peripheral nervous system that results in a general decrease in sensation, was observed in a Honduran man; a few cases of arthrogryposis, a congenital disease characterised by joint deformities, in Brazil are also being suspected to have a Zika link.
Meanwhile, Zika viruses have been found in tears, possibly explaining why some Zika patients have suffered eye diseasee like conjunctivitis and, in rare cases, permanent vision loss. The silver lining in this cloud is that this presents the possibility of testing for Zika, its antibodies or anti-Zika drugs using tears, a less painful way than drawing blood or other methods.
Managing the outbreak
There has been some development on the vaccine development front, including the beginning of what is being called a ‘landmark’ vaccine trial in the US this year. Three types of Zika vaccines were able to provide full protection to rhesus monkeys. The scientists involved in the study say their results are in favour of rapid clinical development of Zika virus vaccines for humans.
A number of compounds have shown promise as drug candidates for Zika, including one that is already in the market as a treatment against tapeworm infection. The 6,000 compounds screened in this study comprised existing compounds already approved by the FDA or at least in clinical trials. The scientists took this approach because screening new compounds would mean years or decades before the drug hits the markets.
Brazilian researchers warned that the Zika epidemic may be under-reported in official statistics, owing in part to some Zika cases being misdiagnosed as dengue. Wrong numbers can undermine the effectiveness of public policy and public health measures, they cautioned.
Back home
Kerala’s health department is trying put put together a strategy to keep the virus out of the state which apart from its high mosquito densities also sees a large travelling population from Singapore. The Hindu quoted a scientist from the state as saying that Kerala has already had an inflow of dengue strain suspected to be from Southeast Asia. Massive alerts, display boards and handout advisories to passengers may be needed, especially since screening for symptoms won’t do (as most Zika cases are symptomless), the same report says.