West Nile Fever


West Nile Fever (FWN) is a disease considered legally contagious in equidae in Morocco, it can have a fatal outcome or leave nerve sequelae after cure in infected animals. Due to its transmissibility to Man and the possible gravity of its evolution in both horses and humans, the FWN can have important economic and hygienic consequences.

FWN is widespread throughout the world including parts of Africa, the Middle East, Asia, Australia, North and South America and Europe. Dispersal and reintroduction of the virus from enzootic areas to areas with sporadic epizootic outbreaks would be carried out by migratory birds.

It is a viral disease transmitted exclusively by the bite of mosquitoes, themselves contaminated via infected birds. Horses and humans are accidental hosts of the virus (epidemiological bag asses), while birds are considered the reservoir of the disease virus.

In equidae, FWN manifests itself either in a febrile form (fever, decrease in general condition, etc.), often inapparente, or in a nervous form (depression, trembling, paresis of the posterior train, ataxia). Spontaneous healing usually occurs within 20 to 30 days of post-infection; however, severe forms with paralysis and death of the animal may occur.

The fight against West Nile fever is mainly based on the application of preventive measures aimed at:

– Immunize horses in risk areas against disease through vaccination that provides adequate protection against disease;

– Protect equidae from mosquitoes in risk areas by using effective deterrents and repellents.

Health situation at national level and control programme

West Nile Fever is a disease deemed legally contagious under Dahir no. 1-06-51 of 14/02/2006 amending and supplementing Dahir no. 1-75-292 of 19 September 1977 enacting measures to guarantee domestic animals against contagious diseases.

Morocco experienced three outbreaks of West Nile fever among equidae in 1996, 2003 and 2010 respectively. Horses were the main species affected. For a disease whose transmission involves vectors (mosquitoes) and reservoirs (birds), it is very likely that the introduction of this disease in Morocco was via migratory birds that stop on the Moroccan coast during their journey from Africa to Europe.

In the event of an outbreak of the disease on a farm, the main steps to take are to:

– put affected holdings under continuous veterinary supervision;

– Immediately report the disease to the ONSSA veterinary services;

– Disinsectisation of infected holdings;

– Sensitize breeders to keep their equidae safe;

– Carry out, according to the epidemiological situation, major operations for the control of vector insects at the level of their cottages of pullulation and multiplication;

– Ensure the strengthening of the surveillance system for the disease at national level, particularly in risk areas, with a view to ensuring early detection of any new outbreaks;

– Perform vaccination in affected areas.

Furthermore, and in view of the risk of recurrence of this disease at national level and in order to reduce the resulting losses in the sensitive population, a code of procedures for the control of said disease by vaccination was developed by ONSSA. This code gives the possibility to equine breeders voluntarily enroll in the FWN vaccination program  and lays down the practical arrangements for its implementation.