West Nile virus reported for the first time in Lebanon

The West Nile virus has never been detected in Lebanon. However, the country is located along the migratory route of birds traveling to and from the Middle East. Serological screening was conducted to assess the potential circulation of this arbovirus. And for the first time, tests were conducted to detect its presence in human, equine, and avian sera. The West Nile virus is transmitted to vertebrates—particularly humans and horses—through mosquito bites, mainly from the genus Culex. Birds are the natural hosts, but they remain largely asymptomatic when infected, except in the United States, where a high mortality rate has been observed. Since the infection is difficult to detect in birds, particularly wild birds, researchers often turn to other affected animals. In humans, the infection remains asymptomatic in 80% of cases. However, some infected individuals develop neurological complications ranging in severity from flu-like symptoms to potentially fatal encephalitis, meningoencephalitis, flaccid paralysis, or Guillain-Barré syndrome. It is therefore important to monitor the circulation of the virus to prevent zoonotic transmission. The West Nile virus is present throughout Africa and in certain countries in Europe, the Middle East, Western Asia, and Australia. Outbreaks occur repeatedly in certain risk areas, particularly along bird migration routes such as Greece, Italy, and Russia. This pathogen is endemic to the Middle East and, more broadly, throughout the Mediterranean region. Human cases of West Nile fever are regularly reported in Israel and Turkey and have even been reported for the first time in Germany (2019 and 2020) and the Netherlands (2020). While serological evidence of the virus’s circulation has been documented in several countries in the region, including Jordan and Egypt, it has never been reported in Lebanon. Yet, like all its neighbors, Lebanon lies along the migratory bird route. A study therefore set out to characterize the circulation of the virus in Lebanon. Researchers analyzed serum samples from humans, horses, and chickens in key geographic areas, looking for antibodies specific to the West Nile virus. Local mosquito populations were also tested for the presence of viral RNA using conventional RT-PCR. While none of the mosquitoes tested were positive, the screening revealed a seroprevalence rate of 1.86% in humans and 2.47% in horses. Contrary to expectations, the seroprevalence rates observed are comparable to those reported in areas of endemicity such as New York (2.6%) or northern Italy (2.08%). However, these results should be interpreted with caution, as the researchers also observed cross-reactions in the ELISA tests, suggesting the circulation of other flaviviruses related to the West Nile virus, such as the Zika, Usutu, and dengue viruses. Serums with very low titers of neutralizing antibodies should therefore be interpreted with caution. Nevertheless, for the first time, local circulation of the West Nile virus has been detected in Lebanon, in both humans and horses. Serological data also revealed exposure to other flaviviruses, including the dengue virus. However, further in-depth studies are needed to determine the identity, lineage, and extent of the spread of these viruses.