Madariaga virus (MADV), or South American eastern equine encephalitis virus (EEEV), has — until now — been found primarily in animals of South and Central America, with the first human outbreak occurring in Panama in 2010. Now, scientists writing in PLOS Neglected Tropical Diseases report the identification of MADV in eight children in Haiti in 2015 and 2016.

MADV can cause outbreaks in horses, and appears to infect a variety of mammals, including rats and bats, and possibly birds and reptiles. However, less than a dozen human cases of MADV infection have been documented, and almost all were encephalitis cases seen as part of an outbreak in Panama.

Glenn Morris of the University of Florida and colleagues maintain a surveillance program since 2014 and they have done a series of studies assessing the etiology of acute febrile illness (AFI) among children in a school cohort in Haiti.

MADV on viral culture of plasma of a student

Unexpectedly, in April, 2015, they identified MADV on viral culture of plasma from a student with AFI in this cohort; an additional seven cases were identified on culture of samples from children with AFI in this same cohort in February, April, and May 2016. On sequence analysis, all strains were very similar genetically, and appear to have come from a strain introduced into Haiti from Panama sometime in the period from October 2012- January 2015. 

Symptoms closely resembled those seen in dengue fever infection

Symptoms from the patients most closely resembled those seen in dengue fever infection, and no patients had encephalitis. All the strains isolated were very similar, and using available information on the genetic sequence of the MADV cultured from the patients, the team was able to hypothesize that the virus was introduced to Haiti from Panama sometime between October 2012 and January 2015.

"Our data indicate that this virus, which has the potential for causing serious illness, has recently been introduced into Haiti, and raises the possibility that it might move into other parts of the Caribbean or North America," the researchers say.

Reports of human infection with MADV are rare, although cross-sectional serologic studies (using plaque-reduction neutralization tests for confirmation) in Panama and Peru have reported seropositivity rates in human populations of between 2 and 5%.