Less than a year after the Haitian government declared that cholera had been eliminated in the country, the disease is infecting thousands of people again.

According to a World Health Organization report from December 13, the country has reported 13,672 cases and 283 deaths since early October.

Haiti's last cholera outbreak started in 2010. Now, in a correspondence from the New England Journal of Medicine, experts are saying that the strain of cholera currently causing another outbreak in Haiti is related to the 2010 strain, and is likely a descendant.

The current outbreak was first reported on October 2, according to the WHO, after three years of no reported cholera cases. Between October 2010 and February 2019, the country reported 820,000 cases and 9,792 deaths from cholera in a massive nationwide outbreak.

In February 2022, the Haitian government declared that cholera had been eliminated in the country.

Cholera causes severe dehydration and spreads through unclean water

Cholera spreads when a person ingests water or food that's infected with a bacteria called Vibrio cholerae. Symptoms include watery diarrhea and dehydration.

Most cases aren't severe, and the WHO said that if proper treatments are available, less than 1 percent of people who become sick die. However, if left untreated, the disease can kill people very quickly.

Treatment includes rehydrating patients with a solution ingested by mouth or pumped through an IV. Currently, there are three oral vaccines the WHO uses that can prevent cholera.

The WHO keeps a stockpile of these vaccines, and the organization sent a shipment of about one million doses of one of these vaccines, called Euvichol, to Haiti on December 12. More cholera vaccines are expected to arrive in Haiti in the coming weeks.

UN troops caused Haiti's last cholera epidemic

The massive 2010 outbreak began after a deadly earthquake in January of that year that was estimated to have killed more than 300,000 people. United Nations troops from Nepal arrived in Haiti in early October of that year.

Before going to Haiti, there had been a cholera outbreak in Kathmandu, where the troops trained before deployment. On October 12, 2010, the first cholera case was reported in Haiti, in a man who bathed and drank from a river two kilometers away from where the troops had set up camp.

In 2011, a panel of experts from the UN determined that the outbreak had begun in a UN camp, and while it did not explicitly say that the troops from Nepal had brought cholera to Haiti, it did say that the strains of cholera from Haiti and from Nepal were "a perfect match." In 2016, the UN finally admitted that it had played a role in the epidemic, though it did not assume legal responsibility.

Scientists don't yet know why this new cholera outbreak is occurring

Scientists aren't yet sure how cholera has reemerged in Haiti after three years of no reported cases.

In a recent New England Journal of Medicine correspondence, the authors proposed three hypothetical reasons that cholera may have cropped up again.

The first is that that cholera cases may have persisted since 2019, but these cases flew under the radar, and now cases are surging once again because of a lack of clean water and sanitation along with falling immunity in the population.

The second is that it may have remained present in environmental reservoirs like rivers or estuaries, where the organism can survive outside of human hosts for multiple days at a time.

The third reason is that cholera may have spread to other countries in Latin America during the 2010 outbreak, and that one of these countries may have reintroduced it to Haiti.

However, the authors say this third option is unlikely, partially because other countries in the region have not reported recent cholera cases.

Whatever the cause of the new cases, the authors said, "These findings, along with the resurgence of cholera in several parts of the world despite available tools to fight it, suggest that cholera control and prevention efforts must be redoubled."

This article was originally published by Business Insider.

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