A 3-year serological and virological cattle follow-up in Madagascar highlands suggests a non-classical transmission route of Rift Valley fever virus.

Rift Valley fever virus (RVFV) is a mosquito-borne infection of livestock and human which causes a potentially severe disease. In 2008-2009, a RVF outbreak occurred in a temperate and mountainous area located on the highlands of Madagascar. A three-year cattle follow-up (2009-2011) was conducted in a pilot area of this highland. A seroprevalence rate of 28% was estimated in 2009 and a seroconversion rate of 7% in 2009-2010. A third cross-sectional survey showed a seroconversion rate of 14% in 2010-2011. In 2011 the longitudinal study suggested a RVFV circulation during the year. In this area where vectors density is low and cattle exchanges are linked to the virus local spread, we raise hypotheses that may explain the local persistence of the virus.