Identification and Pathogenicity Analysis of the Pathogen Causing Spotted Spleen in Muscovy Duck

Abstract

Since September 2020, the clinical symptoms of Muscovy duck spleen spots have appeared in Guangdong, Guangxi, Jiangxi, Hunan, Hubei, and other provinces, resulting in a large number of Muscovy duck deaths and great economic losses. The absence of the typical clinical symptoms caused by pathogenic microorganisms makes the cause of the spotted spleen a mystery. High-throughput sequencing results suggested that Riemerella anatipestifer (R. anatipestifer) may be the pathogen. Then, R. anatipestifer was regarded as the research target for isolation, identification, and pathogenicity assessment. After biochemical test, PCR amplification, and serotype determination, it was confirmed that the isolated strain CZG-1 was serotype 15 R. anatipestifer. Typical spotted spleen symptoms were observed after CZG-1 infection. Furthermore, drug sensitivity assays showed the similar drug-resistant spectrum of R. anatipestifer serotype 15 to other serotypes; for example, all test strains were resistant to polymyxin, gentamicin, and neomycin. The CZG-1 strain has high pathogenicity, and its lethal dose of 50% (LD50) is 35.122 CFU/ml. Virulence gene determination showed that the CZG-1 strain had at least five virulence genes, bioF, TSS9-1, TSS9-2, PncA, and 0373Right. Above all, this study identified and proved that the pathogen of spotted spleen in ducks was R. anatipestifer serotype 15, which caused death of ducks without the typical symptoms of bacterial infection. The results of this study enriched the knowledge of symptom after R. anatipestifer infection, provided a reference to the identification of the pathogen of spotted spleen, and provided theoretical basis for prevention and control of spotted spleen.

Identification of Critical Immune Regulators and Potential Interactions of IL-26 in Riemerella anatipestifer-Infected Ducks by Transcriptome Analysis and Profiling

“…RA infection can cause gross lesions and a spotted spleen with mild pericarditis, liver capsule hepatorrhagia, and cerebral hemorrhage in Muscovy ducks. The infected ducks histo-pathologically develop extensive white myeloid fibrinoid necrosis with a marked loss of cell structure or residual necrotic fragmented nuclei, an unclear boundary between red and white pulp, more diffuse white pulp, and no obvious inflammatory infiltrates in the spleen [9]. Our study showed similar findings, suggesting that RA infection impairs and disorganizes the spleen compartments, affecting the immunological function of the spleen because it is the site of homing and differentiation of immune cells (i.e., macrophages, monocytes, granulocytes, dendritic cells, and plasma cells) [29].…”

“…RA infection can be acute or chronic, with acute infection being more common in ducks younger than 8 weeks of age [7]. Infection is often referred to as new duck disease, riemerellosis, infectious serositis, or duck septicemia, and clinical characteristics include diarrhea, lethargy, ocular and nasal discharge, respiratory symptoms (i.e., dyspnea, mild coughing and sneezing), and nervous symptoms (i.e., tremors of the head and neck or head and legs and ataxia) in addition to pathologic lesions such as fibrinous pericarditis, perihepatitis, airsacculitis, and meningitis [7][8][9][10].…”

“…To date, 21 RA serotypes with differences in virulence, both between and sometimes within a given serotype, have been identified, with less or no significant cross-protection among serotypes [11]. RA outbreaks have been documented in various countries, with the most commonly identified pathogenic isolates reported belonging to serotypes 1, 2, 3, 4, 5, and 15 [4,8,9,[12][13][14]. Treatment for RA infection is carried out using antibiotics, but recent reports have shown drug resistance to various antibiotics, highlighting the need to identify novel therapeutic strategies [12,14].…”

Antibacterial activity of isopropoxy benzene guanidine against Riemerella anatipestifer

“…It incurs high morbidity and mortality rates among waterfowl, resulting in substantial economic losses for the poultry industry across various countries and regions (Tao et al, 2020). R. anatipestifer has numerous serotypes (Ke et al, 2022). Given that no cross immunoprotective effect occurs among these serotypes, vaccine development and disease control for R. anatipestifer infections remains challenging (Chu et al, 2015).…”