A flat, red rash is one of the Zika virus’ first obvious symptoms. But for many people, it simply won’t show.
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Dr Nipon Chinanonwait, director of the Bureau of Vector Borne Diseases, said that measles vaccines — which every Thai child is legally required to receive — can prevent the Zika rash from appearing in patients.
Even in those without the vaccination, Zika patients show symptoms in only about 20% of cases. The result, Dr Nipon said, is that people may have been infected without even knowing.
“It is difficult to identify whether or not a person has Zika,” Dr Nipon said. “This is why the number of infected patients in Thailand is still low. We might have a lot more but no one goes to see the doctor.”
There has been no proper study on how many people in Thailand have been infected with the Zika virus, which was first documented here nearly four years ago. Hospitals are generally more concerned with cases of dengue fever, which has almost identical symptoms but is considered far more dangerous.
Chariya Sangsajja, an infectious diseases expert, told Spectrum that 100,000 people were infected with dengue fever in Thailand last year, with 10% of those considered serious cases. Of those serious cases, there was a 1% mortality rate. By contrast, less than 10 Zika cases were recorded last year, with no serious health repercussions for any of the patients.
UNDER THE RADAR
Transmitted primarily by mosquitoes, the Zika virus is related to dengue and yellow fever. Although it was discovered in the Zika forest in Uganda in 1947 and is common in Africa and Asia, it has largely flown under the radar of health professionals for years as it has never previously been linked to serious health complications.
In Thailand, if a patient arrives at a hospital showing symptoms of Zika — fever, rash and muscle and joint pain — doctors will often check only for the dengue virus; tests for Zika are costly, require specialised equipment and are often seen as unnecessary.
Until recently, Zika was not considered a major threat because its symptoms are relatively mild. Only one of five people infected with the virus develop any symptoms at all, and even among those it is rare that patients have to be hospitalised.
There is no widely available test for Zika infection; because it is closely related to dengue and yellow fever, it may cross-react with antibody tests for those viruses. To detect Zika then, a blood or tissue sample must be sent to an advanced laboratory so the virus can be detected through sophisticated molecular testing.
“This is why Zika is difficult to track,” Dr Nipon said. “It has never been seen as a deadly disease that needs to be treated.”
The cost to check for Zika in Thailand is around 2,000 baht per patient, and only a handful of hospitals across the country are equipped to run the tests. Even then, the virus will only show up in test results if the blood or tissue sample is taken within a week of infection.
MOUNTING CONCERNS
The World Health Organisation last week declared Zika a public health emergency in South America, where in Brazil alone more than 1.5 million people are believed to have been infected with the virus.
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The outbreak there has led to fears that the virus is responsible for a surge in cases of microcephaly, which causes serious brain abnormalities in unborn children.
It is still not known how common microcephaly has become in Brazil’s outbreak — or even if Zika is responsible, although it is strongly suspected that is the case.
About three million babies are born in Brazil each year. Normally, about 150 cases of microcephaly are reported. As of Wednesday, Brazil’s health authorities had logged 4,783 cases of suspected microcephaly since the outbreak began late last year. The majority of those are likely false positives: All babies with a head circumference of less than 32 centimetres are flagged as a suspected case, regardless of the potential cause. Of the 1,313 cases the government has investigated so far, around a third, or 404, were confirmed to have microcephaly. The diagnosis was rejected in the remaining cases.
TRACING THE SPREAD
With the Zika virus existing in Asia for years, many have been left wondering why concerns over the risk of microcephaly are only now coming to light.
The virus is thought to have reached Asia from Africa at least 50 years ago, though it’s not clear when it arrived in Thailand. While it may have caused spikes in microcephaly as it first spread, there was no testing to pin down which of many possible causes was to blame.
In 2007, a Southeast Asian strain of the Zika virus began leapfrogging the South Pacific, sparking rapid outbreaks on islands where no one had immunity to it. Because island populations are small, rare side effects did not occur often enough to be noticed. But in 2013, during an outbreak in French Polynesia, which has 270,000 residents, doctors confirmed 42 cases of Guillain-Barre syndrome, which can cause paralysis. That was about eight times the normal number and the first hint that Zika virus can attack the nervous system, which includes the brain.
On Friday, Colombia confirmed the first three deaths of patients infected with the Zika virus who had contracted Guillain-Barre syndrome.
The possibility that the Zika virus causes microcephaly emerged only in October, when doctors in northern Brazil noticed a surge in babies with the condition.
It may be that other factors, such as simultaneous infection with other viruses, are contributing to the rise; investigators may even find that Zika virus is not the main cause, although right now circumstantial evidence suggests that it is.
‘NOT DANGEROUS’
During outbreaks of potentially deadly communicable diseases such as Sars or Ebola, only one Thai hospital is properly equipped to handle cases: the Bamrasnaradura Infectious Diseases Institute.
Dr Chariya, the institute’s director, told Spectrum that an average of five Zika cases have been recorded in Thailand per year since the first case was documented here in 2012.
The first case was recorded in Phetchabun province, home to dense jungles and high mosquito populations. In 2013, cases were documented more widely, in Phetchabun, Phuket, Krabi and Bangkok.
Dr Chariya said it was impossible to conclude when the virus arrived in Thailand, as few hospitals were equipped to test for it and doctors had previously been largely unconcerned by the ability of the virus to cause serious harm.
“Zika virus is not at all dangerous. In fact, the human body can heal itself from this virus,” Dr Chariya said.
“The virus will stay in the human body for between two and seven days. Then the immune system will help fight the virus and finally kill it.”
For most, the infection causes no symptoms and leads to no lasting harm. Scientific concern is focused on women who become infected while pregnant, and a rare number of patients who develop a temporary form of paralysis after exposure to the Zika virus.
Experts believe that the vast majority of all Zika infections are transmitted by mosquitoes, although at least three cases have shown it may also be passed on during sex.
It is possible the virus has mutated, according to Raina MacIntyre, head of the school of public health and community medicine at the University of New South Wales in Australia. It is also possible that widespread exposure to other flaviviruses such as dengue could confer some degree of protection to people in Asia, she said.
DON’T WORRY, BE VIGILANT
In Thailand, health authorities remain largely unconcerned. After a meeting last week, they announced that there was no outbreak here and urged people not to panic, noting the virus was still far less dangerous than dengue fever or malaria, which are far more prevalent and are also considered dangerous for pregnant women.
Amnuay Kajina, the director for the Disease Control Department, told Spectrum there is nothing to fear in Thailand at this stage, and that people should continue to take the same standard precautions they would against other vector-borne diseases.
“There is nothing to worry about here. The situation is under control,” Dr Amnuay said. “What we can do is to destroy mosquito breeding grounds, especially stagnant water around people’s homes.”
People should also protect themselves against mosquito bites by using insect repellent, wearing clothes that cover as much of the body as possible, and using physical barriers such as screens, closed doors and windows, the WHO has warned.
Dr Amnuay said it was essential that pregnant women monitor their health closely throughout their full term — advice he said was standard even before fears of a Zika outbreak.
“If you are carrying a baby and start to develop a skin rash, please go to see a doctor and have yourself checked to make sure that there are no unwanted diseases that can be passed on to your baby,” Dr Amnuay said. “It may or may not be Zika. But there are many other diseases, such as measles, that can be just as dangerous to an unborn baby.”
Dr Amnuay said part of the reason why Zika had taken on epidemic status in South America could be because of global warming and climate change. Mosquitoes can spread their eggs much better and much longer especially in the country like Thailand and many countries in South East Asia. “We are not issuing any travel warning … But anyone who travelled to the affected area and came back with a high fever is recommended to go to a designated hospital to get a check up,” Dr Amnuay said.
SAFE, NOT SORRY
With no known treatment or vaccination for Zika, WHO Southeast Asia regional director Poonam Khetrapal Singh said prevention remains the best cure. He is urging countries across the region to strengthen surveillance and take preventive measures against the virus.
He said the Zika virus is of concern in Southeast Asia as the Aedes aegyptii mosquito, responsible for its spread, is found in many areas and there is little evidence of immunity to the virus among people in the region.
Dr Chariya recommended everyone monitor their health closely, especially pregnant women.
“If you suspect that you are sick with any disease at all, you should come to see a doctor. Getting sick during pregnancy is always a risk, since diseases can be passed on to your baby,” Dr Chariya said. “Consulting with a doctor if there is any threat to the health of your child is extremely important.”
CAUSE FOR CONCERN: The BMA plans to boost efforts to destroy mosquito larvae to fight against vector-borne diseases like Zika and dengue fever.
