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Are Aedes mosquitoes in Singapore now transmitting the Zika virus?

By Chris Kuan

The modes of transmission of the Zika infection is through the Aedes mosquito while transmission through sexual intercourse is documented and through, blood transfusion and organ transplant are also considered  potential risks.

Did those infected have unprotected sex, blood transfusion and organ transplant - I don't know but the last two seems very unlikely. If they did not get it from unprotected sex, then they would have gotten Zika from the Aedes mosquito, the same mosquito that caused dengue.

So far it seems that the type of Aedes mosquito that is capable of transmitting Zika is the Aedes Aegypti species, other species are considered potential vectors of the disease. What more is that it is the Aedes Aegypti that is the main vector for dengue in Singapore. In addition, the Aedes Albopictu species, a less efficient vector for dengue is found to be capable of transmitting Zika under experimental conditions.

Zika fever symptoms are mild which leave it commonly undiagnosed and it is also often mistaken for dengue and tested for it would turn out to be negative. It appears there has been no reported fatalities from the fever so far.

So the crucial question is whether the Aedes Aegypti and Albopictu species of mosquitoes in Singapore are now transmitting the Zika virus.

This does raise the question of what the MOH know or don't know. According to this report from the Centers for Disease Control and Prevention (CDC) in United States, it appears that the Zika virus (ZIKV) is not unknown in our region.

The report writes,

"In Asia, Zika fever has been described sporadically in Cambodia, Thailand, and Indonesia (Java and Lombok). On the basis of the incubation time of ≈6 days in returning travelers, we assumed that the patient became infected in Keningau or surrounding villages, in northern Borneo. Although ZIKV was detected in Ae. aegypti mosquitoes in peninsular Malaysia in 1969 and antibodies against ZIKV were demonstrated in serum samples from 15 of 79 patients on peninsular Malaysia and 9 of 50 patients in Borneo in 1953, Zika fever in peninsular Malaysia or Borneo has not been reported. In 2001, ZIKV seropositivity was demonstrated in a native Bornean, 2 migrants to Borneo, and 2 Bornean orangutans (Pongo pygmaeus) . A later study found an additional 8 Bornean orangutans to be seropositive for antibodies against ZIKV (10). Thus, in Borneo, either the virus only rarely infects humans or the disease is mistaken for dengue fever".

A patient in Germany contracted the virus after travelling through Borneo back in 2014. It had already occurred back in the 1950s and 1960s although rare. It is very likely that previous ZIKV infections, symptoms being mild has been undiagnosed or misdiagnosed as dengue.

The disease is not new, what is new is the global awareness of it due to increasing incidence first reported in Brazil.

Editor's note - Speaking to a doctor specialising in infectious disease, it is true that the Zika virus has been around the region even to a point of 60 years back. As the transmission of the virus has been limited and the symptoms are largely mild, people have lived with the virus without knowing it existed, as one will be immune to the virus after one has been infected and recovers from the infection.

On the sudden increase of Zika infections, it is possible that clusters emerge due to the presence of mosquito breeding grounds and other factors.

It is now crucial that MOH to test whether the virus from the confirmed cases of Zika infection is the same strand as those of South American or is that of regional variations so that we can know the origin of the infections.