Viral haemorrhagic septicaemia virus IVb experimental infection of rainbow trout, Oncorhynchus mykiss (Walbaum), and fathead minnow, Pimphales promelas (Rafinesque)

• Published in: Journal of fish diseases Vol. 33; no. 4; pp. 347 - 360
• Main Authors: Al-Hussinee, L, Huber, P, Russell, S, LePage, V, Reid, A, Young, K.M, Nagy, E, Stevenson, R.M.W, Lumsden, J.S
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01.04.2010; Blackwell Publishing Ltd
• Subjects: Animals; Antigens, Viral - metabolism; Cyprinidae; Disease Susceptibility - veterinary; experimental infection; fathead minnow; Fish Diseases - mortality; Fish Diseases - pathology; Freshwater; Immunohistochemistry; Novirhabdovirus - physiology; Oncorhynchus mykiss; Pimephales promelas; rainbow trout; Rhabdoviridae Infections - mortality; Rhabdoviridae Infections - pathology; Rhabdoviridae Infections - veterinary; Time Factors; VHSV IVb; viral haemorrhagic septicaemia virus; Viral hemorrhagic septicemia virus; North America, Great Lakes
• ISSN: 0140-7775; 1365-2761
• DOI: 10.1111/j.1365-2761.2009.01128.x

Viral haemorrhagic septicaemia virus (VHSV) in the Great Lakes has had a dramatic impact on fish husbandry because of the implications of the presence of a reportable disease. Experimental infections with VHSV IVb were conducted in rainbow trout, Oncorhynchus mykiss (Walbaum), and fathead minnows, Pimphales promelas (Rafinesque), to examine their susceptibility and the clinical impact of infection. Triplicate groups of rainbow trout (n = 40) were injected intraperitoneally (i.p.) with 100 μL 10⁶.⁵50% tissue culture infective doses (TCID₅₀) or waterborne exposed to graded doses (10⁴.⁵, 10⁶.⁵, and 10⁸.⁵ TCID₅₀ mL⁻¹) of VHSV IVb. Duplicate groups of fathead minnows (n = 15) were i.p. injected with (10⁶.⁵ TCID₅₀ 100 μL) or waterborne exposed (10⁶.⁵ TCID₅₀ mL⁻¹). All experiments were performed with single-pass well water maintained at 12 °C. Following either i.p. or waterborne exposure, VHSV RNA was detectable in both rainbow trout and fathead minnows by nested reverse transcription polymerase chain reaction (nRT-PCR) as early as 4-7 days post-infection (p.i.). Infected fathead minnow and rainbow trout exhibited lesions characteristic of VHS at 9 and 15 days p.i., respectively. Route of exposure had little effect on the onset of clinical signs. Cumulative mean mortality in rainbow trout was 4.4%, 2.6%, 2.6% and less than 1% in the i.p., high, medium and low dose waterborne exposures, respectively. Cumulative average mortality of 50% and 13% occurred in i.p. and waterborne-exposed fathead minnows, respectively. VHSV was detected from pooled rainbow trout tissue by RT-PCR and virus isolation at 38 days p.i., but not at 74 days p.i., regardless of the exposure route. Immunohistochemistry (IHC) with a rabbit antibody to VHSV IVb revealed the viral tissue tropisms following infection, with the identification of viral antigen in myocardium and necrotic branchial epithelium of both species and in gonadal tissue of fathead minnows. Rainbow trout, but not fathead minnows, are relatively refractory to experimental infection with VHSV IVb.