CARACAS (Reuters) - Around 1 million unvaccinated Venezuelan children are susceptible to measles, a highly contagious disease that has re-emerged in the crisis-stricken South American nation, a group of doctors estimated on Friday.

A crippling shortage of medicines and vaccines, as well as decaying hospitals and an exodus of doctors has thrown Venezuela’s health sector into a tailspin.

Amid the crisis, once-controlled diseases like diphtheria and measles have returned to the fore, putting Venezuela’s 30 million people at risk and raising the threat of contagion beyond its borders.

Measles, caused by a virus usually passed through direct contact and the air, is a top cause of death for young children although a vaccine is available. The World Health Organization warns it can be especially lethal in countries that have suffered violent conflict and whose health infrastructure is deteriorated.

Venezuelan health associations first raised the alarm about the return of measles in the rough southern mining state of Bolivar in August. Since then, the WHO has reported 84 suspected cases, with 34 confirmed cases.

“Preliminary data indicates it is evolving rapidly,” two Venezuelan public health organizations said of the measles outbreak in a report on Friday.

“We’ve identified a suboptimal vaccination coverage, and on a national level we estimate that at least 1,150,000 children under the age of 1 were not vaccinated... over the last 10 years,” the report added.

Ana Carvajal, a doctor and one of the authors of the report, told Reuters the estimate is based on data obtained through sources at the Health Ministry and WHO figures.

Still, an ongoing vaccination drive in Bolivar has likely lowered the risk.

The WHO has said it is helping with the purchase and delivery of some 7.2 million vaccines against measles, mumps and rubella (MMR) in Venezuela and hopes to spread the drive across the country.

As Venezuela’s medical crisis has worsened, the Health Ministry has largely kept mum and no longer publishes a weekly bulletin that includes data on infant mortality or mosquito-borne diseases like malaria.

The government did not respond to a request for comment on this story.

Measles deaths dropped around 79 percent between 2000 and 2015 globally thanks to vaccinations, according to the WHO.

But gaps in coverage have lead to several measles outbreaks in Europe in the past year, officials said in April, with lack of trust leading people to turn down potentially life-saving vaccines.