Molecular characterization of the Newcastle disease virus that caused an outbreak in backyard birds in Costa Rica in 2015

Costa Rica gained its Newcastle Disease Virus NDV-free status with vaccination according to OIE proceedings in 1996, and its declaration as a country free of the velogenic, viscerotropic form of this disease (G/SPS/GEN/119) presented to the World Trade Organization (WTO) in 1999. On April 24th, 2015, SENASA (National Animal Health Service) attended a velogenic Newcastle disease outbreak that affected backyard chickens in a small town (Bellavista, Guanacaste) in the northern part of the country, near the Nicaraguan border. Sixty-five backyard birds died from a total of 84 exposed animals. Blood samples, cloacal swabs, tracheal swabs, cecal tonsils, lung and trachea tissues were collected for diagnosis at the National Veterinary Services Laboratory (LANASEVE). These samples were screened for Avian Influenza (AIV) and NDV. All samples were negative for Avian Influenza in ELISA test and RT-PCR. Serum samples were positive for NDV antibody by hemagglutination inhibition test, and tissue and swab samples were positive for NDV by conventional RT-qPCR targeting a 310 bp fragment of the virus fusion protein gene. The amino acid sequence of the protease cleavage site within the amplicon matched the sequence of a virulent strain (112RRQKRF117). The nucleotide sequence had a 98.7% identity and an e value of 4e-153 with a genotype V velogenic sequence from Belize (KF767467) and Honduras (JN872194) collected in 2008 and 2007, respectively, according to BLASTN. A total of 3604 backyard birds were euthanized in town and its surroundings (1 km), including 3495 chickens, 66 turkeys, 6 geese, and 37 ducks. The case was considered resolved, and OIE was notified in November 2015 following OIE guidelines. In April 2017, Costa Rica recovered its disease-free status through executive decree No. 40301-MAG.