Shrimp health is an especially important topic for preventing and minimizing losses and the negative impact on the production chain. Among the diseases that affect shrimp are infection with the infectious myonecrosis virus (IMNV), which belongs to the Totiviridae family, and infection with the infectious hematopoietic and hypodermic necrosis virus (IHHNV), a type of parvovirus. Transmission occurs through reproduction or ingestion of material contaminated with the virus.
The Official Veterinary Service of the Distrito Federal (SEAGRI-DF) was notified of a 30% mortality rate in a batch of grey shrimp (Penaeus vannamei) with animals showing whitish spots, poor performance and non-uniformity of animal size. A total of 30 moribund individuals were collected and preserved in 95% ethanol solution for molecular analysis at the Federal Agricultural Defense Laboratory of the Ministry of Agriculture, Livestock and Food Supply (LFDA/GO) and a further 10 shrimp for complementary histopathology tests at the Veterinary Pathological Diagnostic Laboratory of the University of Brasília (LDPV/UnB). Macroscopic and microscopic anatomopathological evaluations of the animals were carried out at the University of Brasilia, using Davidson’s solution to fix the structures. They were then cleaved into multiple fragments (transverse and longitudinal), stored in cassettes and routinely processed for histopathology. Phylogenetic analyses to determine the origin of the viruses are underway.
Decapod penstyldensovirus 1-PstDV1/ IHHNV and IMNV were detected in the LFDA/GO using qPCR and RT-qPCR techniques, respectively. In addition to these, the pathogens Vibrio parahaemolyticus-Vp (Acute Hepatopancreatic Necrosis Syndrome-AHPND), White spot syndrome virus-WSSV and Taura syndrome virus-TSV were also investigated, resulting in no detection.
This is the first report of these viruses on a farm in the Brazilian Central Plateau, where there is continental shrimp farming that produces mainly in closed and super-intensive systems.
Phylogenetic analyses have not yet been completed, but there is evidence that the viruses found in the Distrito Federal are phylogenetically close to the strains found in the Northeast of Brazil, since the
vast majority of hatcheries that sell post-larvae in the country are located in that region.
In the pathological examination at the UnB, macroscopy showed multifocal, blackish or whitish millimetric areas, with moderate loss of transparency in the animals. Microscopy revealed multifocal necrotizing myositis with interfascicular edema and the formation of a spherical lymphoid organ. No eosinophilic intranuclear inclusion corpuscles were found, which are characteristic of IHHNV infection. But the great non-uniformity of animal size typical of this disease corroborates the molecular detection. After diagnosis, the official veterinary service carried out outbreak elimination and disinfection protocols.
In conclusion, this was the first record of IMNV and IHHNV in shrimp farming in the Central Plateau of Brazil, being a case of co-infection of two viruses present in states of the Northeast region of Brazil. The record serves as a warning to shrimp farmers and veterinary services in other regions of Brazil to define strategies to prevent the introduction of these viruses, which are mainly present in northeastern Brazil.