Comparative quantitative monitoring of rabbit haemorrhagic disease viruses in rabbit kittens

Abstract

BackgroundOnly one strain (the Czech CAPM-v351) of rabbit haemorrhagic disease virus (RHDV) has been released in Australia and New Zealand to control pest populations of the European rabbit O. cuniculus. Antigenic variants of RHDV known as RHDVa strains are reportedly replacing RHDV strains in other parts of the world, and Australia is currently investigating the usefulness of RHDVa to complement rabbit biocontrol efforts in Australia and New Zealand. RHDV efficiently kills adult rabbits but not rabbit kittens, which are more resistant to RHD the younger they are and which may carry the virus without signs of disease for prolonged periods. These different infection patterns in young rabbits may significantly influence RHDV epidemiology in the field and hence attempts to control rabbit numbers.MethodsWe quantified RHDV replication and shedding in 4–5 week old rabbits using quantitative real time PCR to assess their potential to shape RHDV epidemiology by shedding and transmitting virus. We further compared RHDV-v351 with an antigenic variant strain of RHDVa in kittens that is currently being considered as a potential RHDV strain for future release to improve rabbit biocontrol in Australia.ResultsKittens were susceptible to infection with virus doses as low as 10 ID50. Virus growth, shedding and transmission after RHDVa infection was found to be comparable or non-significantly lower compared to RHDV. Virus replication and shedding was observed in all kittens infected, but was low in comparison to adult rabbits. Both viruses were shed and transmitted to bystander rabbits. While blood titres indicated that 4–5 week old kittens mostly clear the infection even in the absence of maternal antibodies, virus titres in liver, spleen and mesenteric lymph node were still high on day 5 post infection.ConclusionsRabbit kittens are susceptible to infection with very low doses of RHDV, and can transmit virus before they seroconvert. They may therefore play an important role in RHDV field epidemiology, in particular for virus transmission within social groups during virus outbreaks.

Increased virulence of rabbit haemorrhagic disease virus associated with genetic resistance in wild Australian rabbits ( Oryctolagus cuniculus )

“…In contrast, RHDV can be transmitted both orally by fomites or direct contact between rabbits (26), and passively via insect vectors, with the latter likely responsible for the escape of RHDV from quarantine in 1995 (45). While fomite/contact transmission is likely to play an important role in transmission during virus outbreaks (46), long distance transmission of RHDV occurs through flies that scavenge on decomposing carcasses, or fresh carcasses opened by predators, and then transmit the virus passively by landing on mucous membranes of rabbits directly, or by leaving faeces or regurgita on pasture that is subsequently ingested by rabbits (45, 47, 48). Hence, MYXV requires vectors to bite a live, diseased animal.…”

Nitazoxanide: A first-in-class broad-spectrum antiviral agent

“…Studies of the mechanism of action of nitazoxanide against influenza viruses have shown that the drug blocks maturation of the viral hemagglutinin at the post-translational stage (Rossignol et al, 2009a). The drug had no effect on the other glycoprotein, neuraminidase, the target of oseltamivir and zanamivir, or the M2 protein, the target of amantadine, and it had no effect on viral infectivity, adsorption or entry into target cells (La Frazia et al, 2013;Rossignol et al, 2009a;Shi et al, 2014).…”

Efficacy of a commercial vaccine against different strains of rabbit haemorrhagic disease virus

“…1 A vaccine designed to protect against RHD (Cylap®, Fort Dodge Cyanamid, USA) was registered for use in Australia in late 1995. 6 This study investigates the efficacy of the Cylap® RHD vaccine in rabbits exposed to very high doses of the K5 and v351 strains of RHDV. In common with many other commercial vaccines, there is little efficacy data in the peer-reviewed scientific literature.…”