Tonga, a country located 5,200km from the Australian mainland, has declared a Zika epidemic.

The island kingdom tested a sample group of 260 Tongans and found five were infected with the mosquito-borne virus linked to birth defects, prompting it to issue the warning.

Dr Reynold Ofanoa, the chief medical officer at Tonga’s Department of Public Health, said none of the confirmed cases were pregnant women.

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“The reason why we declared it a Zika epidemic is … [authorities] noticed an increase in patients coming in with acute fever and rash,” he told the ABC.

“We took some blood tests … and we had five confirmed cases.”

This is the latest development in a growing global crisis, which the the UN’s World Health Organisation has declared an international health emergency.

The virus is transmitted to people through the bite of infected female Aedes mosquitoes, the same type of mosquito that spreads dengue, chikungunya and yellow fever.

There is no treatment or vaccine available for Zika infection. Companies and scientists are racing to develop a safe and effective vaccine for Zika, but one is not expected to be ready for months or years.

The Pan American Health Organisation (PAHO) has said there is no evidence the virus can kill, but some cases have been reported with more serious complications in patients with pre-existing medical conditions.

The virus is “strongly suspected” of causing microcephaly. Photo: Getty

There is as yet no definitive proof that Zika causes birth defects, but an abnormally high rate of microcephaly cases in Brazil has been tentatively linked to the virus. Microcephaly causes shrunken brain and skulls and possible brain damage to developing babies in the womb.

People who get Zika virus disease typically have a mild fever, skin rash, conjunctivitis, muscle and joint pain and fatigue that can last for two to seven days. But as many as 80 per cent of people infected never develop symptoms.

Because there is no vaccine, efforts to control Zika’s spread focus on eliminating mosquito breeding sites and taking precautions against mosquito bites such as using insect repellent and mosquito nets.

Travellers have been warned of the risk of infection in countries across the Americas, Southern Asia and the Western Pacific. These include: Brazil (the worst affected), Barbados, Bolivia, Colombia, Costa Rica, Curacao, Dominican Republic, Ecuador, El Salvador, French Guiana, Guadeloupe, Guatemala, Guyana, Haiti, Honduras, Jamaica, Martinique, Mexico, Nicaragua, Panama, Paraguay, Puerto Rico, Saint Martin, Samoa, Suriname, Venezuela and the US Virgin Islands.

The zirus is thought to have started in Ugandan monkeys or chimpanzees. Photo: Getty

Tonga is the latest country to be added to this growing list, with many more expected.

The virus will spread “explosively”, the World Health Organisation has warned.

The Zika virus is found in tropical locales with large mosquito populations. It was first identified in Uganda in 1947 in monkeys and was first identified in people in 1952 in Uganda and Tanzania.

The WHO says because no big Zika outbreaks were recorded before 2007, little is known about complications caused by infection.

During an outbreak of Zika from 2013-2014 in French Polynesia, national health authorities reported an unusual increase in Guillain-Barre syndrome. Health authorities in Brazil have also reported an increase in the rare disorder, which causes the body’s immune system to attack part of the nervous system.

-with ABC and AAP