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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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RHDV and RHDVa replication, excretion and tissue distribution in rabbit kittens. Shown are virus genome copy numbers per μl whole blood (A, B) or rectal swab (C, D) as measured via RT-qPCR in samples from RHDV (A, C) and RHDVa (B, D) infected kittens 4–5 weeks of age at the indicated time points. SDL indicates the genome concentration relative to 20 genome copies detected in the RT-qPCR, which is considered the safe detection limit. E: Virus loads in tissues of RHDV and RHDVa infected kittens, 5 dpi. The safe detection limit of our assay in these tissues was 400 genome copies/mg on average (range 140–678 depending on the amount of tissue used for RNA extraction) or 20 genome copies/μl bile.
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Figure 3: RHDV and RHDVa replication, excretion and tissue distribution in rabbit kittens. Shown are virus genome copy numbers per μl whole blood (A, B) or rectal swab (C, D) as measured via RT-qPCR in samples from RHDV (A, C) and RHDVa (B, D) infected kittens 4–5 weeks of age at the indicated time points. SDL indicates the genome concentration relative to 20 genome copies detected in the RT-qPCR, which is considered the safe detection limit. E: Virus loads in tissues of RHDV and RHDVa infected kittens, 5 dpi. The safe detection limit of our assay in these tissues was 400 genome copies/mg on average (range 140–678 depending on the amount of tissue used for RNA extraction) or 20 genome copies/μl bile.

Mentions: To compare RHDV-v351 and the potential candidate RHDVa strain, we infected six kittens with 700 ID50 of RHDV and in parallel six kittens with a similar amount of RHDVa (approximately 2000 ID50 as titrated in adult rabbits). Low levels of replication were observed for the RHDV-v351 strain, with peak genome copy numbers in blood after 2 dpi (Figure 3A), except for one kitten that showed a pronounced viremia until the end of the experiment (day 5). RHDVa genome copy numbers of up to 280 genome copies/μl blood were observed, but median genome concentrations were lower than observed for RHDV (Figure 3B). Genome copy numbers in swab samples were comparable at day 4 and 5 between RHDV and RHDVa (Figure 3C, D). Concentrations of genome copy numbers in mesenteric lymph node, spleen, liver, duodenum and bile did not differ significantly in RHDV and RHDVa infected kittens at autopsy, 5 dpi (Figure 3E), indicating a similar tissue specificity. In line with the low level of virus replication, we only saw signs of RHD at autopsy in one RHDV infected kitten (RHDV 3–3) that had a pale liver.


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)

RHDV and RHDVa replication, excretion and tissue distribution in rabbit kittens. Shown are virus genome copy numbers per μl whole blood (A, B) or rectal swab (C, D) as measured via RT-qPCR in samples from RHDV (A, C) and RHDVa (B, D) infected kittens 4–5 weeks of age at the indicated time points. SDL indicates the genome concentration relative to 20 genome copies detected in the RT-qPCR, which is considered the safe detection limit. E: Virus loads in tissues of RHDV and RHDVa infected kittens, 5 dpi. The safe detection limit of our assay in these tissues was 400 genome copies/mg on average (range 140–678 depending on the amount of tissue used for RNA extraction) or 20 genome copies/μl bile.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 3: RHDV and RHDVa replication, excretion and tissue distribution in rabbit kittens. Shown are virus genome copy numbers per μl whole blood (A, B) or rectal swab (C, D) as measured via RT-qPCR in samples from RHDV (A, C) and RHDVa (B, D) infected kittens 4–5 weeks of age at the indicated time points. SDL indicates the genome concentration relative to 20 genome copies detected in the RT-qPCR, which is considered the safe detection limit. E: Virus loads in tissues of RHDV and RHDVa infected kittens, 5 dpi. The safe detection limit of our assay in these tissues was 400 genome copies/mg on average (range 140–678 depending on the amount of tissue used for RNA extraction) or 20 genome copies/μl bile.
Mentions: To compare RHDV-v351 and the potential candidate RHDVa strain, we infected six kittens with 700 ID50 of RHDV and in parallel six kittens with a similar amount of RHDVa (approximately 2000 ID50 as titrated in adult rabbits). Low levels of replication were observed for the RHDV-v351 strain, with peak genome copy numbers in blood after 2 dpi (Figure 3A), except for one kitten that showed a pronounced viremia until the end of the experiment (day 5). RHDVa genome copy numbers of up to 280 genome copies/μl blood were observed, but median genome concentrations were lower than observed for RHDV (Figure 3B). Genome copy numbers in swab samples were comparable at day 4 and 5 between RHDV and RHDVa (Figure 3C, D). Concentrations of genome copy numbers in mesenteric lymph node, spleen, liver, duodenum and bile did not differ significantly in RHDV and RHDVa infected kittens at autopsy, 5 dpi (Figure 3E), indicating a similar tissue specificity. In line with the low level of virus replication, we only saw signs of RHD at autopsy in one RHDV infected kitten (RHDV 3–3) that had a pale liver.

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