Streptococcosis in Nile tilapia Farming: A Severe yet Overlooked Health Challenge in Mexico, a Study Case in Campeche, Mexico

Streptococcosis is a bacterial disease that causes significant economic losses in Nile tilapia farming worldwide. An Outbreaks of Streptococcus agalactiae was detected in grow-out ponds on a farm in Campeche, Mexico. This study is the first to describe and analyze the histopathological damages, economic losses, and clinical manifestations of S. agalactiae in a commercial farm in Campeche, Mexico. A total of 30 Nile tilapia exhibiting clinical signs of the disease were collected in May 2023. Necropsies of the affected fish revealed characteristic signs of streptococcosis, including bilateral exophthalmia, nodules in the spleen, hemorrhagic brain, hepatomegaly, spleen congestion and accumulation of fluid in the abdominal cavity. Nile tilapia organs (brain, liver, kidney, muscle, spleen, stomach and intestine) were removed and fixed in 10 % formalin for histopathological examination. Histopathological alterations in tissues showed significant internal organ damage, characterized by a granulomatous reaction, melanomacrophage pigment, vacuolar degeneration, and granular eosinophilic cells containing evident bacterial bodies. Alterations in organs tissues were graded by severity scores. We analyzed information on biomass losses caused by S. agalactiae from January to December 2022. The Monte Carlo simulation show economic losses of streptococcosis at 30,740 kg of Nile tilapia per year, translating to a financial impact of averaged $1,537,671 ± 34,2587 Mexican pesos (76464.53 ± 17036 USD). Additionally, the disease reached an 80% prevalence rate, resulting in high mortality and morbidity rates among the fish. The prognosis for streptococcosis in Mexico is concerning, given that it is recognized as one of the most significant diseases affecting cultivated Nile tilapia. Despite the severe impacts of streptococcosis outbreaks on the environment, public health, and socio-economics, there remains a notable data gap regarding the disease’s epidemiology in Mexico. It is crucial to generate more scientific information on diagnosis, prevalence, pathogen distribution, natural historical variation, newly identified serotypes, and potential zoonotic cases.