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Comparative quantitative monitoring of rabbit haemorrhagic disease viruses in rabbit kittens.

Matthaei M, Kerr PJ, Read AJ, Hick P, Haboury S, Wright JD, Strive T - Virol. J. (2014)

Bottom Line: These different infection patterns in young rabbits may significantly influence RHDV epidemiology in the field and hence attempts to control rabbit numbers.Virus growth, shedding and transmission after RHDVa infection was found to be comparable or non-significantly lower compared to RHDV.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Commonwealth Scientific and Industrial Research Organisation - Ecosystem Sciences, ACT 2601 Black Mountain, Australia. tanja.strive@csiro.au.

ABSTRACT

Background: Only 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.

Methods: We 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.

Results: Kittens 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.

Conclusions: Rabbit 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.

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Virus genome copy numbers in samples from rabbit kittens inoculated with heat inactivated RHDV. Kittens were inoculated with 1 ml heat-inactivated (hi) RHDV containing 9x10e8 genome copies (equivalent to 2000 ID50). Kittens were sampled daily until autopsied at day 5. A: Virus genome copy numbers per μl blood; B: Genome copy numbers in rectal swab samples. SDL indicates the genome concentration relative to 20 genome copies detected in the RT-qPCR reaction, which is considered the safe detection limit.
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Figure 2: Virus genome copy numbers in samples from rabbit kittens inoculated with heat inactivated RHDV. Kittens were inoculated with 1 ml heat-inactivated (hi) RHDV containing 9x10e8 genome copies (equivalent to 2000 ID50). Kittens were sampled daily until autopsied at day 5. A: Virus genome copy numbers per μl blood; B: Genome copy numbers in rectal swab samples. SDL indicates the genome concentration relative to 20 genome copies detected in the RT-qPCR reaction, which is considered the safe detection limit.

Mentions: To estimate to what extent we detect inoculum or virus progeny due to a productive infection when measuring genome copy numbers, we also inoculated five kittens orally with heat-inactivated virus. Heat-inactivation has been shown to best preserve genome copy numbers measurable by RT-qPCR compared to chemical inactivation procedures [44,45]. RT-qPCR analysis showed a drop of 55% in genome copy numbers in heat-inactivated virus stock compared to untreated virus preparation (9×108 genome copies per millilitre heat-inactivated stock, equivalent to 2000 ID50/ml). After inoculation of 1 ml heat-inactivated virus, we measured only trace amounts of virus genomes in daily blood samples (Figure 2A) and in autopsy samples taken at 5 dpi (liver, mesenteric lymph node, spleen, duodenum and bile, data not shown). In contrast, rectal swabs did contain detectable viral genomes with a median of up to 730 genomes per swab between day 1 and 4 (Figure 2B). Therefore, 100-fold higher median viral genome concentrations per swab as measured for untreated virus (compare Figure 1B to Figure 2B) between 1 to 7 dpi, very likely indicate RHDV replication and do not reflect inoculated virus alone. All five kittens inoculated with heat-inactivated virus were serologically negative for RHDV-specific IgM at 5 dpi, indicating that virus replication had not occurred.


Comparative quantitative monitoring of rabbit haemorrhagic disease viruses in rabbit kittens.

Matthaei M, Kerr PJ, Read AJ, Hick P, Haboury S, Wright JD, Strive T - Virol. J. (2014)

Virus genome copy numbers in samples from rabbit kittens inoculated with heat inactivated RHDV. Kittens were inoculated with 1 ml heat-inactivated (hi) RHDV containing 9x10e8 genome copies (equivalent to 2000 ID50). Kittens were sampled daily until autopsied at day 5. A: Virus genome copy numbers per μl blood; B: Genome copy numbers in rectal swab samples. SDL indicates the genome concentration relative to 20 genome copies detected in the RT-qPCR reaction, which is considered the safe detection limit.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4060863&req=5

Figure 2: Virus genome copy numbers in samples from rabbit kittens inoculated with heat inactivated RHDV. Kittens were inoculated with 1 ml heat-inactivated (hi) RHDV containing 9x10e8 genome copies (equivalent to 2000 ID50). Kittens were sampled daily until autopsied at day 5. A: Virus genome copy numbers per μl blood; B: Genome copy numbers in rectal swab samples. SDL indicates the genome concentration relative to 20 genome copies detected in the RT-qPCR reaction, which is considered the safe detection limit.
Mentions: To estimate to what extent we detect inoculum or virus progeny due to a productive infection when measuring genome copy numbers, we also inoculated five kittens orally with heat-inactivated virus. Heat-inactivation has been shown to best preserve genome copy numbers measurable by RT-qPCR compared to chemical inactivation procedures [44,45]. RT-qPCR analysis showed a drop of 55% in genome copy numbers in heat-inactivated virus stock compared to untreated virus preparation (9×108 genome copies per millilitre heat-inactivated stock, equivalent to 2000 ID50/ml). After inoculation of 1 ml heat-inactivated virus, we measured only trace amounts of virus genomes in daily blood samples (Figure 2A) and in autopsy samples taken at 5 dpi (liver, mesenteric lymph node, spleen, duodenum and bile, data not shown). In contrast, rectal swabs did contain detectable viral genomes with a median of up to 730 genomes per swab between day 1 and 4 (Figure 2B). Therefore, 100-fold higher median viral genome concentrations per swab as measured for untreated virus (compare Figure 1B to Figure 2B) between 1 to 7 dpi, very likely indicate RHDV replication and do not reflect inoculated virus alone. All five kittens inoculated with heat-inactivated virus were serologically negative for RHDV-specific IgM at 5 dpi, indicating that virus replication had not occurred.

Bottom Line: These different infection patterns in young rabbits may significantly influence RHDV epidemiology in the field and hence attempts to control rabbit numbers.Virus growth, shedding and transmission after RHDVa infection was found to be comparable or non-significantly lower compared to RHDV.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: Commonwealth Scientific and Industrial Research Organisation - Ecosystem Sciences, ACT 2601 Black Mountain, Australia. tanja.strive@csiro.au.

ABSTRACT

Background: Only 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.

Methods: We 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.

Results: Kittens 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.

Conclusions: Rabbit 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.

Show MeSH
Related in: MedlinePlus