WEBVTT - Special Episode: Rabbit Hemorrhagic Disease Virus 0:00:43.600 --> 0:00:47.040 Hi, I'm Aaron Welsh and this is this podcast will 0:00:47.120 --> 0:00:50.800 kill You. I'm back with another bonus episode in our 0:00:50.880 --> 0:00:53.960 mini series of bonus content that will be releasing over 0:00:54.000 --> 0:00:57.160 the next few months. In case this is the first 0:00:57.200 --> 0:01:00.520 bonus episode you're tuning into and you're wondering what the 0:01:00.560 --> 0:01:03.760 heck is going on, I'm using these episodes as an 0:01:03.760 --> 0:01:07.520 opportunity to explore more about whatever disease or topic we 0:01:07.600 --> 0:01:10.800 covered in our previous week's episode, and also to get 0:01:10.840 --> 0:01:14.480 to chat with experts about their jobs, their hopes, their dreams, 0:01:14.600 --> 0:01:18.160 whatever comes to mind. If you've listened to the podcast before, 0:01:18.600 --> 0:01:21.520 you know that I'm kind of a relentless question asker, 0:01:22.000 --> 0:01:24.679 and so instead of just pestering Aaron Updyke with all 0:01:24.680 --> 0:01:28.600 the questions, I'm saving some for these episodes, and so 0:01:28.760 --> 0:01:31.959 far I've gotten to have some great conversations with people 0:01:32.080 --> 0:01:36.400 in very different careers, studying or working on very different problems. 0:01:36.800 --> 0:01:40.040 And this week I am so excited to have yet 0:01:40.080 --> 0:01:43.720 another fun conversation and learn a whole lot more about 0:01:43.760 --> 0:01:47.000 another topic. So what am I going through be talking 0:01:47.040 --> 0:01:50.160 about today? This week really kind of picks up where 0:01:50.160 --> 0:01:53.080 we left off in our most recent regular season episode. 0:01:53.440 --> 0:01:56.400 Which covered a virus of rabbits called the Maxoma virus. 0:01:56.960 --> 0:01:59.280 If you haven't listened to that episode yet, I would 0:01:59.320 --> 0:02:02.480 recommend check it out before listening to this, just because 0:02:02.560 --> 0:02:06.160 there's so much more to that story, but I'll give 0:02:06.200 --> 0:02:09.800 a quick recap here. The Maxoma virus is a type 0:02:09.840 --> 0:02:13.320 of poxvirus that can cause severe disease in some species 0:02:13.320 --> 0:02:16.639 of rabbits, and it became internationally famous back in the 0:02:16.760 --> 0:02:20.320 nineteen fifties when it was introduced to Australia as part 0:02:20.360 --> 0:02:24.760 of efforts to control the invasive European rabbit population. What 0:02:24.840 --> 0:02:28.040 had started out as a handful of European rabbits introduced 0:02:28.040 --> 0:02:31.600 to Australia in eighteen fifty nine had within a few 0:02:31.639 --> 0:02:37.360 decades grown to an absolute ecological and agricultural menace. Entire 0:02:37.440 --> 0:02:43.240 ecosystems were disrupted, native animals experienced tremendous population declines, many 0:02:43.320 --> 0:02:47.440 plant species were driven locally or regionally extinct, and huge 0:02:47.480 --> 0:02:50.400 tracts of land could no longer be used for agriculture. 0:02:51.120 --> 0:02:54.200 The introduction of the Maxoma virus did help to drive 0:02:54.280 --> 0:02:59.240 down or stabilize rabbit populations, but over generations the virus 0:02:59.280 --> 0:03:02.080 lost a bit of its impact. As both rabbit and 0:03:02.240 --> 0:03:06.320 mixomavirus adapted to one another, the deadly virus was no 0:03:06.400 --> 0:03:09.079 longer as deadly as it once was, and the rabbit 0:03:09.280 --> 0:03:11.560 was no longer as susceptible as it used to be. 0:03:12.400 --> 0:03:15.839 So when another lethal virus of European rabbits was identified 0:03:15.880 --> 0:03:20.359 in the nineteen eighties, the rabbit hemorrhagic disease virus or RHDV, 0:03:21.240 --> 0:03:24.480 it was explored as another possible form of biocontrol for 0:03:24.560 --> 0:03:28.519 rabbits in Australia, and RHDV was introduced in the mid 0:03:28.639 --> 0:03:32.799 nineteen nineties, again helping to keep rabbit populations under control. 0:03:33.680 --> 0:03:36.720 But the story of rabbits in Australia doesn't end there, 0:03:37.080 --> 0:03:40.520 and neither does the story of the rabbit hemorrhagic disease virus. 0:03:41.160 --> 0:03:43.680 In twenty ten, a new type of the virus was 0:03:43.720 --> 0:03:48.320 discovered in France, the aptly named rabbit hemorrhagic disease virus 0:03:48.360 --> 0:03:51.600 type two, and this one doesn't seem limited to just 0:03:51.760 --> 0:03:57.000 European rabbit populations. Since its discovery, RHDV two has spread 0:03:57.040 --> 0:04:00.360 around the world and has led to concerns for demmestic 0:04:00.400 --> 0:04:03.160 pet rabbits as well as the wild rabbits and hairs 0:04:03.160 --> 0:04:06.760 that are susceptible, especially in places which have already seen 0:04:06.920 --> 0:04:11.960 damaging ecological cascades from RHDV one. So what I really 0:04:12.000 --> 0:04:16.480 wanted to explore in this bonus episode was these two viruses. 0:04:16.360 --> 0:04:18.880 RHDV one and rhdv two. 0:04:19.320 --> 0:04:21.640 Where did they come from? What effects have they had 0:04:21.680 --> 0:04:25.799 on rabbit populations? Are they following the same evolutionary patterns 0:04:25.839 --> 0:04:29.560 as maxomavirus, How worried should we be? And to help 0:04:29.600 --> 0:04:33.159 me answer these questions and so many more, is doctor 0:04:33.240 --> 0:04:37.279 Robin Hall, veterinary virologist and team leader for the rabbit 0:04:37.320 --> 0:04:43.040 Biocontrol team at CSIRO, the Commonwealth Scientific and Industrial Research Organization, 0:04:43.360 --> 0:04:46.840 which is a government agency in Australia. I am super 0:04:46.920 --> 0:04:50.360 excited to jump into this interview, so I'll just take 0:04:50.440 --> 0:04:52.799 a quick break here and then we'll get started. 0:05:16.839 --> 0:05:18.520 Hi. I'm Robin Hall. 0:05:18.680 --> 0:05:23.200 I'm a veterinary virologist and epidemiologist at the Commonwealth Scientific 0:05:23.279 --> 0:05:28.479 and Industrial Research Organization or CSIRO, based in Canberra, Australia, 0:05:29.240 --> 0:05:31.880 team leader for the rabbit buyer Control team here, and 0:05:32.400 --> 0:05:37.560 I have a special interest in host pathogen interactions, management 0:05:37.600 --> 0:05:40.839 of invasive species and viral evolution. 0:05:41.800 --> 0:05:42.240 Awesome. 0:05:42.480 --> 0:05:45.000 Thank you so much for taking the time to chat 0:05:45.000 --> 0:05:45.559 with me today. 0:05:45.600 --> 0:05:50.760 I am thrilled thanks for the opportunity. It's really exciting 0:05:50.760 --> 0:05:51.039 for me. 0:05:51.880 --> 0:05:55.359 So in our episode on mixed and mitosis, Erin and 0:05:55.400 --> 0:05:58.520 I talked a lot about the long history of European 0:05:58.600 --> 0:06:02.479 rabbits in Australia and how this invsive species has been 0:06:02.680 --> 0:06:07.360 incredibly damaging both ecologically and economically, and I was wondering 0:06:07.440 --> 0:06:09.200 if you could bring us up to speed on the 0:06:09.200 --> 0:06:12.200 current situation with rabbits in Australia, like what do we 0:06:12.320 --> 0:06:15.279 know about the impact that they're still having and where 0:06:15.320 --> 0:06:18.440 does their continued presence seem to be the most problematic. 0:06:19.680 --> 0:06:22.080 You know, back in the nineteen fifties, rabbits were at 0:06:22.200 --> 0:06:26.240 massive plague proportions throughout Australia, and then with the introduction 0:06:26.320 --> 0:06:30.359 of mixomavirus, it was incredibly effective in reducing population numbers, 0:06:30.800 --> 0:06:34.080 but of course populations begin to recover over time, and 0:06:34.160 --> 0:06:37.960 so in the mid nineties RHDV or rabbit hemorrhagic disease 0:06:38.080 --> 0:06:42.880 virus was released again with massive declines in rabbit populations, 0:06:43.240 --> 0:06:45.719 but over time. You know, bio controls are not a 0:06:45.760 --> 0:06:50.040 silver bullet, and once more rabbit populations began to increase, 0:06:50.240 --> 0:06:53.760 and so that led to in twenty seventeen, the release 0:06:53.800 --> 0:06:56.680 of a new variant of RHDV, which we call K 0:06:56.880 --> 0:07:00.680 five in Australia, and again we're still seeing the impacts 0:07:00.680 --> 0:07:04.240 from both the K five release and the arrival of 0:07:04.279 --> 0:07:07.480 this new virus, rhdiv two in Australia which was not 0:07:07.520 --> 0:07:11.080 deliberately released but has spread here as it has globally. 0:07:11.720 --> 0:07:17.400 And so currently rabbit populations are relatively suppressed to comparatively 0:07:17.440 --> 0:07:19.280 to what they have been in the past, but we 0:07:19.360 --> 0:07:23.160 do still see considerable impacts, and these fluctuate on a 0:07:23.160 --> 0:07:25.240 bit of a boom and bust cycle. You know, when 0:07:25.360 --> 0:07:28.160 conditions are good, the populations will breed very rapidly and 0:07:28.240 --> 0:07:31.000 increase in size, and if we go into a period 0:07:31.000 --> 0:07:35.280 of drought, then populations can decline again. So the impacts 0:07:35.320 --> 0:07:40.840 we see are really most obvious in environmentally sensitive areas, 0:07:41.040 --> 0:07:44.240 so particularly in the arid and semi arid zones where 0:07:44.320 --> 0:07:49.120 rabbits compete with native species for food and shelter, and 0:07:49.160 --> 0:07:52.560 they eat native plants that are already finding it difficult 0:07:52.600 --> 0:07:55.600 to grow in these arid conditions. And then obvious course 0:07:55.600 --> 0:07:59.680 in agricultural industries as well, where they impact crops through grazing, 0:08:00.200 --> 0:08:03.040 they damage the soil, they compete with livestock for food, 0:08:03.120 --> 0:08:06.320 and again particularly in drought conditions, those impacts are more severe. 0:08:06.880 --> 0:08:11.280 And they also Rabbits also have some perhaps less considered impacts, 0:08:11.280 --> 0:08:15.240 so things like they impact our indigenous cultural heritage sites 0:08:15.320 --> 0:08:20.440 by damaging these artifacts and sacred sites and things, and 0:08:20.920 --> 0:08:24.320 even the impact of reducing the vegetation. I mean that 0:08:24.360 --> 0:08:27.000 then exposes more soil, and the soil can then blow 0:08:27.080 --> 0:08:27.520 into the. 0:08:27.480 --> 0:08:29.840 Fleece of sheep which reduces fleace quality. 0:08:30.200 --> 0:08:33.240 So there's this really sort of lead on effects and 0:08:33.400 --> 0:08:36.160 they really have dramatic impacts that are quite wide ranging 0:08:36.200 --> 0:08:37.800 and both direct and indirect. 0:08:39.360 --> 0:08:43.080 Our last episode focused on one of the most impactful 0:08:43.120 --> 0:08:46.840 tools for rabbit control in Australia, of course, the maxomavirus, 0:08:47.240 --> 0:08:51.120 and we also briefly mentioned the rabbit hemorrhagic disease virus, 0:08:51.120 --> 0:08:52.720 which I cannot wait. 0:08:52.600 --> 0:08:53.600 To ask you more about. 0:08:54.280 --> 0:08:58.000 But these two biocontrol agents, they're not the only tools 0:08:58.120 --> 0:09:01.040 used to try to suppress rabbit population, So can you 0:09:01.080 --> 0:09:03.320 talk about the other methods that are used. 0:09:04.480 --> 0:09:06.880 When we talk about a control tool, you really want 0:09:06.920 --> 0:09:12.040 something that's going to be effective, relatively cheap or easy 0:09:12.080 --> 0:09:15.880 to distribute, and viruses are really the only thing that 0:09:15.920 --> 0:09:18.240 we have that are self disseminating that work on a 0:09:18.320 --> 0:09:23.200 landscape scale with the existing technologies. However, certainly at local 0:09:23.360 --> 0:09:25.040 levels there are a lot of other tools that can 0:09:25.080 --> 0:09:29.560 be used. So particularly poisons are used quite heavily, so pindone, 0:09:29.600 --> 0:09:32.600 but also ten eighty so pin done is an anticoagulant, 0:09:32.720 --> 0:09:35.360 so it's like rat baits sort of, and ten eighty 0:09:35.440 --> 0:09:39.560 as a metabolic topsin. We also focus a lot on 0:09:39.840 --> 0:09:44.120 habitat removal, so destroying the warrens or if they're harboring 0:09:44.280 --> 0:09:48.719 in you know, shrubs, removing the shrubbery where possible shooting 0:09:48.760 --> 0:09:52.600 and trapping can be employed. On a local level, exclusion 0:09:52.640 --> 0:09:55.360 fencing has been applied so where you you know, put 0:09:55.440 --> 0:09:57.680 up fences that keep the rabbits out, but again you 0:09:57.760 --> 0:10:00.560 have to dig it down and put it up relative high. 0:10:00.600 --> 0:10:04.600 And then warren fumigation where you introduce like a gas 0:10:04.640 --> 0:10:08.000 into the warren to kill them. So all of those 0:10:08.080 --> 0:10:11.480 other methods they are very effective at local levels, but 0:10:11.640 --> 0:10:15.160 as you can imagine, they're quite labor intensive and certainly, 0:10:15.240 --> 0:10:18.160 you know we can't use them across the landscape scale 0:10:18.440 --> 0:10:19.280 of Australia. 0:10:20.800 --> 0:10:23.200 So now I am so excited because I get to 0:10:23.240 --> 0:10:26.000 ask about rabbit hemorrhagic disease virus. 0:10:26.240 --> 0:10:28.440 I read that this is a calisivirus. 0:10:28.640 --> 0:10:29.680 What does that mean? 0:10:29.880 --> 0:10:32.160 Like, are there other types of callisi viruses? 0:10:33.280 --> 0:10:36.800 Yep, I'm very happy to talk about URHDV as well. 0:10:37.800 --> 0:10:43.760 So yeah, RHDV is a kalisivirus. These are small RNA viruses. 0:10:43.800 --> 0:10:46.200 So like the coronavirus is an RNA virus as well, 0:10:46.200 --> 0:10:49.559 it has an RNA genome, but coronaviruses have like thirty 0:10:49.640 --> 0:10:53.720 thousand letters in their genetic code, whereas these caliciviruses have 0:10:53.840 --> 0:10:55.760 like seven and a half thousand letters, So we call 0:10:55.840 --> 0:10:57.679 them small RNA viruses. 0:10:58.240 --> 0:10:59.520 The shell or the. 0:10:59.480 --> 0:11:02.800 Capsid that the genome is packaged into is non enveloped, 0:11:03.080 --> 0:11:06.600 and so that means that they're incredibly environmentally resistant. So 0:11:06.760 --> 0:11:09.520 like I think, again, we hopefully all know now with 0:11:09.640 --> 0:11:14.120 coronavirus that you know, it doesn't survive particularly long on surfaces, 0:11:14.559 --> 0:11:17.000 and it does use droplets and things like that, it's 0:11:17.040 --> 0:11:20.800 protected in that moist droplet environment, whereas kalisivirus is because 0:11:20.800 --> 0:11:24.240 they're non enveloped, they can survive on surfaces or in 0:11:24.360 --> 0:11:30.080 soil or something for months. Chalciviruses are pretty common and 0:11:30.240 --> 0:11:35.600 probably occur in most, if not all, vertebrate species, although 0:11:35.640 --> 0:11:38.680 we are really only starting to look at the virus 0:11:38.720 --> 0:11:41.800 sphere more broadly, but some that you may have heard 0:11:41.840 --> 0:11:46.400 of would include like human neurovirus, feline chalicivirus, so it's 0:11:46.400 --> 0:11:49.880 something that we vaccinate our pet cats for. And then 0:11:49.920 --> 0:11:54.080 there are kalsiviruses of you know, cows, mice, pigs, chickens, 0:11:54.240 --> 0:11:58.240 atlantic salmon, so yeah, it's a big family, and the 0:11:58.320 --> 0:12:00.640 rabbit and hair ones there as well. 0:12:01.760 --> 0:12:05.720 How are these viruses transmitted, or maybe in particular, how 0:12:05.840 --> 0:12:07.600 is RHDV transmitted? 0:12:08.679 --> 0:12:12.120 A lot of the calisi viruses are transmitted by the 0:12:12.520 --> 0:12:16.160 fecal oral roots, so you know, you ingest them either 0:12:16.320 --> 0:12:19.160 from a contaminated surface or something like that, and then 0:12:19.200 --> 0:12:22.000 they replicating the body they're passed out in the feces 0:12:22.040 --> 0:12:26.400 and then contaminate their environment, and so RHDV broadly follows 0:12:26.400 --> 0:12:31.480 that process. However, because again this environmental stability, RHDV can 0:12:31.520 --> 0:12:35.400 also get picked up mechanically by insects, so particularly carryon flies. 0:12:35.840 --> 0:12:40.120 The typical life circle for an rhdv virus is it's 0:12:40.320 --> 0:12:43.439 ingested somehow, so either you know, the grass is contaminated 0:12:43.440 --> 0:12:45.760 and the rabbit eats it, or the rabbit sniffs a 0:12:45.920 --> 0:12:48.840 dead rabbit and gets it in that way, or a 0:12:48.840 --> 0:12:53.200 blowfly comes and lands on like the eyelids of a 0:12:53.200 --> 0:12:55.959 healthy rabbit and deposits some virus there, and then the 0:12:56.000 --> 0:12:58.760 rabbit rooms itself and eats it the virus that way. 0:12:59.120 --> 0:13:03.640 The virus then go into the gut, enters the animals 0:13:03.679 --> 0:13:07.199 systemically and causes this major infection that we can talk 0:13:07.240 --> 0:13:11.840 about in the second and then the rabbit dies typically 0:13:12.120 --> 0:13:15.800 within forty six to seventy two hours post infection, so 0:13:15.920 --> 0:13:20.480 this thing is incredibly incredibly fast. And then the carcass 0:13:20.520 --> 0:13:24.240 starts to break down and contaminates the environment and the 0:13:24.280 --> 0:13:26.079 flies can come in and pick it up and move 0:13:26.120 --> 0:13:27.440 it between populations. 0:13:28.960 --> 0:13:31.880 What's going on at the path of physiological level, and like, 0:13:31.960 --> 0:13:34.240 what's a typical course of infection? 0:13:34.360 --> 0:13:35.160 What does that look like? 0:13:36.160 --> 0:13:40.600 So from the outside you frequently don't see clinical signs, 0:13:40.640 --> 0:13:43.000 which I guess is great from a by control perspective, 0:13:43.040 --> 0:13:46.560 because the welfare is actually I mean, anything that kills 0:13:46.600 --> 0:13:48.760 something you don't want to say welfare is good, but 0:13:48.920 --> 0:13:51.800 it certainly has less impact on the animal than something 0:13:51.840 --> 0:13:55.360 like say mixomavirus. So many pet owners, you know, we 0:13:55.480 --> 0:13:58.240 often hear that, oh, it was fine, it was eating 0:13:58.240 --> 0:13:59.760 the night before I came in in the morning it 0:13:59.800 --> 0:14:02.760 was and so you often find them still with food 0:14:02.760 --> 0:14:05.400 in their mouth. And so it does happen very quickly, 0:14:05.400 --> 0:14:08.600 and frequently you don't see any clinical signs in the 0:14:08.679 --> 0:14:11.920 rabbit unless you're sort of taking temperatures every few hours 0:14:12.000 --> 0:14:15.680 or something at the path of physiological level. Basically, what 0:14:15.760 --> 0:14:18.760 happens is the virus goes in. It targets the liver, 0:14:19.080 --> 0:14:21.960 so it starts to replicate in the liver, and it 0:14:22.000 --> 0:14:25.920 causes this massive hepatitis that all a liver cell start 0:14:25.960 --> 0:14:29.640 to bust open and the liver just pretty much disintegrates, 0:14:29.720 --> 0:14:32.880 I guess, And so that leads to you know, a 0:14:32.960 --> 0:14:36.600 cytokine storm as such, and so you get this massive 0:14:36.760 --> 0:14:42.680 systemic inflammatory response syndrome, disseminated intravascular coagulation and you know, 0:14:42.760 --> 0:14:46.040 circulatory shock and death. And so that sounds all very 0:14:46.120 --> 0:14:50.040 awful and it is, I guess, but it's a fairly 0:14:50.040 --> 0:14:53.040 typical hemorrhagic fever virus so you know, some people have 0:14:53.240 --> 0:14:55.720 referred to it as bunny a bola and things like that, 0:14:55.840 --> 0:14:58.840 But basically, the virus goes in, causes a lot of 0:14:58.920 --> 0:15:03.000 damage to the internal organs, sets up this massive inflammatory response, 0:15:03.080 --> 0:15:04.760 and then the body's just overwhelmed. 0:15:06.160 --> 0:15:08.200 And so is that courus of infection? 0:15:08.480 --> 0:15:13.200 Is that fairly consistent across individuals within a population. 0:15:13.200 --> 0:15:14.239 Or within a species? 0:15:14.800 --> 0:15:18.040 And how variable is that a cross species as well? 0:15:19.240 --> 0:15:23.920 So RHDV is incredibly species specific. So there's a couple 0:15:23.920 --> 0:15:28.360 of different variants of RHDV. RHDV one was like the 0:15:28.400 --> 0:15:31.440 original RHDV that was first reported in sort of the 0:15:31.640 --> 0:15:37.320 nineteen eighties, and that RHDV one only affect European rabbits, 0:15:37.360 --> 0:15:40.560 so there's no definitive evidence that it can replicate in 0:15:40.600 --> 0:15:44.560 any other species. Then in twenty ten, a new variant 0:15:44.600 --> 0:15:48.360 called RHDV two emerged, and what we saw with RHGV 0:15:48.400 --> 0:15:52.280 two is that it can also infect other lagomorph species, 0:15:52.360 --> 0:15:56.800 so hares or jack rabbits, the Lepis species, and then 0:15:56.840 --> 0:16:00.600 also the cottontails or the silver lagas species. But still 0:16:00.880 --> 0:16:04.200 people are looking and have looked, and there's no evidence 0:16:04.240 --> 0:16:09.240 of any disease outside of those lagomorph species, within a species, 0:16:09.320 --> 0:16:14.600 or within individuals, within naive individuals. Certainly, the disease courses 0:16:14.880 --> 0:16:18.440 is pretty typical, and we see a case fatality rate, 0:16:18.640 --> 0:16:21.840 you know, upwards of ninety five percent, ninety nine percent, 0:16:22.000 --> 0:16:25.520 So it's it is very very consistent. In animals that 0:16:25.560 --> 0:16:28.680 have some degree of pre existing immunity, then the infection 0:16:28.800 --> 0:16:32.600 can look quite different. So you may get prolonged infections, 0:16:32.640 --> 0:16:35.760 they may get a subclinical heptitis with jaundice and things 0:16:35.800 --> 0:16:39.680 like that, and then secondary liver disease. But again that 0:16:39.760 --> 0:16:41.720 sort of depends on the level of immunity. But in 0:16:41.840 --> 0:16:45.760 naive individuals, it's very very consistent with an extraordinarily high 0:16:45.880 --> 0:16:46.920 case fatality rate. 0:16:48.120 --> 0:16:50.560 Where did these viruses come from? What do we know 0:16:50.800 --> 0:16:55.480 about the origins either of RHGV one or RHDV two. 0:16:56.560 --> 0:16:59.840 Yeah, I mean, where the viruses come from, that's the question. 0:17:01.240 --> 0:17:06.840 It is so certainly, you know, when i HGV one 0:17:07.040 --> 0:17:10.800 emerged in the nineteen eighties, it was reported in Angora 0:17:10.880 --> 0:17:14.800 rabbits in China. These rabbits are being bred for and 0:17:14.920 --> 0:17:17.119 they just observed these mass mortality events, so it was 0:17:17.119 --> 0:17:20.360 pretty clear that something was going on, and they identified 0:17:20.600 --> 0:17:22.639 this virus and later it was found to be a 0:17:22.680 --> 0:17:26.160 Callesi virus and things like that. So we're fairly confident that, 0:17:26.240 --> 0:17:28.880 you know, it wasn't around beforehand or for a long 0:17:28.880 --> 0:17:31.160 period of time beforehand, because we would have seen these 0:17:31.200 --> 0:17:35.399 math mortality events. A couple of hypotheses as to how 0:17:35.680 --> 0:17:39.240 that virus emerged. It could have either been a species jump, 0:17:39.280 --> 0:17:42.439 so the same thing as mixomavirus. You know, it's completely 0:17:42.520 --> 0:17:47.000 subclinical in its natural reservoir host, but when it transmits 0:17:47.040 --> 0:17:50.639 to European rabbits, it becomes highly virulent in that species, 0:17:50.680 --> 0:17:55.800 and so that is one hypothesis. Or it could be recombination. 0:17:56.600 --> 0:18:00.560 So these viruses recombined, so basically different parts the genome 0:18:00.600 --> 0:18:03.760 sort of switch in and switch out, and that can 0:18:03.920 --> 0:18:07.359 give the virus different characteristics. And so it could be that, 0:18:07.960 --> 0:18:11.240 you know, if there was a benign kalisivirus present in rabbits, 0:18:11.280 --> 0:18:14.520 which we know rabbits do have several benign rabbit Colisi 0:18:14.600 --> 0:18:16.800 viruses that just infect the gut, they don't cause that 0:18:16.840 --> 0:18:21.080 systemic disease. And if that benign virus then acquired virulence, 0:18:21.280 --> 0:18:25.800 either through just standard viral evolution or probably more likely 0:18:26.080 --> 0:18:29.919 through a recombination event with something, then that could have 0:18:30.040 --> 0:18:33.840 led to the emergence of this highly virulent rabbit calisi virus. 0:18:33.840 --> 0:18:38.840 Similarly with RHDV two, all known RHDV twos actually contain 0:18:39.280 --> 0:18:43.720 part of their genome from other rabbit calisi viruses, and 0:18:43.760 --> 0:18:46.680 then it's the RHDV two capsid that's the new part 0:18:46.800 --> 0:18:49.120 and that gives it the broader host range and things 0:18:49.119 --> 0:18:51.560 like that. So the capsid is the shell of the virus. 0:18:52.000 --> 0:18:54.840 And so where those capsid genes came from again, we 0:18:54.920 --> 0:18:59.080 don't know. Was it just through natural evolution or was 0:18:59.119 --> 0:19:03.240 it a recombination event with another calicivirus. So two main 0:19:03.320 --> 0:19:08.120 hypotheses cross species jump or evolution from a benign ancestor. 0:19:08.720 --> 0:19:12.720 So how did RHDV two get to be globally distributed 0:19:12.720 --> 0:19:15.960 because it was only found in twenty ten, but now 0:19:16.000 --> 0:19:18.960 it has this global distribution, So what do we know 0:19:19.000 --> 0:19:20.000 about how that happened. 0:19:21.119 --> 0:19:25.879 That's been the really incredible thing is seeing the how 0:19:26.160 --> 0:19:31.520 RHDV two has become globally distributed so rapidly. It's really 0:19:31.560 --> 0:19:34.640 been incredible observing this sort of in real. 0:19:34.520 --> 0:19:36.399 Time and a bit horrifying. 0:19:36.520 --> 0:19:41.720 But so again we know that it's an incredibly environmentally 0:19:41.960 --> 0:19:45.760 resistant virus, and so it can survive and remain infectious 0:19:45.800 --> 0:19:50.000 for months in the environment. And then I think the 0:19:50.040 --> 0:19:53.440 other thing that's contributed to that is that because there's 0:19:53.480 --> 0:19:56.280 not a lot of cross protection or imminological cross protection 0:19:56.359 --> 0:20:00.560 between RHDV one and RHDV two, RHDV two very rapidly 0:20:00.960 --> 0:20:03.880 replaced rh tov one. So I guess the analogy here 0:20:03.880 --> 0:20:07.959 would be the RTV two is the omicron of rabbit 0:20:08.160 --> 0:20:11.600 caliciviruses replacing delta. And so you know, there was this 0:20:11.720 --> 0:20:15.480 huge surge in cases because it swept through an effectively 0:20:16.119 --> 0:20:20.440 naive population, so you had huge case numbers. The virus 0:20:20.480 --> 0:20:23.879 grows to extremely high levels and infected rabbits, and so 0:20:24.040 --> 0:20:28.639 there was just this massive virus load being shed into 0:20:28.640 --> 0:20:32.840 the European environment after the emergence and local Europeans spread 0:20:32.920 --> 0:20:37.919 and so then with global travel and globalization, you know, 0:20:37.960 --> 0:20:40.520 if people walked across a park where a rabbit had died, 0:20:40.560 --> 0:20:42.440 they pick it up on their shoes and then they 0:20:42.480 --> 0:20:45.760 travel and take it home, you know, and if it 0:20:45.760 --> 0:20:49.160 gets into a wild rabbit population anywhere, then it spreads 0:20:49.400 --> 0:20:51.880 that way. And I think we saw a similar thing 0:20:51.920 --> 0:20:56.280 with the emergence of canine pavovirus back in the mid seventies. 0:20:56.760 --> 0:21:00.840 Parvoviruses are also incredibly environmentally resistant, and we saw that 0:21:00.880 --> 0:21:04.639 spread globally within about six months actually, so we know 0:21:04.760 --> 0:21:09.600 that environmentally resistant viruses just through bomite transmission, can you know, 0:21:09.640 --> 0:21:12.800 transmission on shoes and things like that. I think the 0:21:12.920 --> 0:21:15.640 other thing that I don't have a lot of data on, 0:21:15.720 --> 0:21:19.720 but I really didn't appreciate. I guess so much before 0:21:19.840 --> 0:21:23.879 RHGV two how much trade of rabbits and rabbit equipment 0:21:24.080 --> 0:21:27.040 particularly there are. So I think, you know, it could 0:21:27.119 --> 0:21:29.280 be that if somebody's pet rabbit dies, they then put 0:21:29.280 --> 0:21:32.320 the cage on eBay or something, and somebody else orders 0:21:32.359 --> 0:21:35.000 the cage and then the cage is contaminated. And so 0:21:35.760 --> 0:21:38.480 again I certainly don't have direct evidence for that, but 0:21:38.560 --> 0:21:42.320 I think it's it's easy to sell stuff internationally these 0:21:42.400 --> 0:21:45.120 days and ship stuff, and so I suspect that there 0:21:45.200 --> 0:21:46.760 may be some of that as well. 0:21:47.880 --> 0:21:50.000 I want to talk about sort of the impact of 0:21:50.119 --> 0:21:53.440 RHDV two in Australia in a minute, but I want 0:21:53.480 --> 0:21:57.080 to first ask about some of these places where RHDV 0:21:57.240 --> 0:22:01.440 one or RHDV two has spread and where rabbits are 0:22:01.480 --> 0:22:04.080 not considered invasive where they're, you know, just a part 0:22:04.160 --> 0:22:07.960 of the natural ecosystem. What have we seen in terms 0:22:08.000 --> 0:22:11.359 of the impact on the local rabbit populations there, and 0:22:11.400 --> 0:22:14.760 what kind of downstream effects have there been on the 0:22:14.840 --> 0:22:16.440 other members of that ecosystem. 0:22:17.600 --> 0:22:17.800 You know. 0:22:17.880 --> 0:22:21.320 The impacts of RHDV first RGV one are now URHDV 0:22:21.400 --> 0:22:24.879 two on rabbit populations in their native home range is 0:22:24.960 --> 0:22:27.760 really concerning and it's actually caused them to be their 0:22:27.760 --> 0:22:30.760 threat category to be upgraded in terms of the IC 0:22:30.880 --> 0:22:34.040 and Red List. So it really is a major concern 0:22:34.400 --> 0:22:38.000 for native rabbit populations. And so rabbits are native to 0:22:38.200 --> 0:22:43.520 the Iberian Peninsula, so Portugal and Spain, and they've certainly 0:22:43.560 --> 0:22:47.800 observed sixty to seventy percent declines in rabbit populations, and 0:22:47.840 --> 0:22:51.960 then they've also observed similar reductions on their apex predators, 0:22:52.040 --> 0:22:55.560 so the Iberian links in the Spanish Imperial Eagle, particularly 0:22:56.160 --> 0:22:59.080 because those animals don't have the food source, and that 0:22:59.160 --> 0:23:02.600 then effects for tea of those populations and so they're 0:23:02.600 --> 0:23:07.080 not breeding as effectively, and so rabbits really are keystone species. 0:23:06.640 --> 0:23:07.760 In their native environment. 0:23:08.359 --> 0:23:12.399 Similarly, RGB two arrived in the US in early twenty 0:23:12.440 --> 0:23:16.760 twenty and we've seen quite dramatic impacts on cottontail and 0:23:16.840 --> 0:23:19.440 jack rabbit populations in the US, and certainly there are 0:23:19.520 --> 0:23:24.119 several endangered species over there, and so there's quite grave 0:23:24.160 --> 0:23:27.480 concerns about the impacts of RHGB two on those already 0:23:27.720 --> 0:23:31.359 threatened populations. Likely there'll be similar lead on effects on 0:23:31.400 --> 0:23:35.679 their predators as well. I don't know that the reductions 0:23:35.720 --> 0:23:38.680 have actually been quantified at this point in the US, 0:23:39.000 --> 0:23:41.440 and I think the other thing, you know, I've had 0:23:41.440 --> 0:23:43.720 some conversations with colleagues in the US and they've sort 0:23:43.760 --> 0:23:45.840 of said, we haven't really seen the knockdowns that we 0:23:46.160 --> 0:23:48.760 you know, you've reported in Australia that we're seen in Europe. 0:23:49.000 --> 0:23:52.239 And I think that's probably at least partially due to 0:23:52.359 --> 0:23:55.200 the different ecology of the cottontails and jack rabbits over there. 0:23:55.200 --> 0:23:58.719 So I believe that they don't form these massive warren 0:23:58.840 --> 0:24:02.240 systems same way that rabbits do. The contact densities are 0:24:02.240 --> 0:24:04.280 probably lower, and things like that. 0:24:05.240 --> 0:24:08.400 A lot of people who are concerned about this are 0:24:08.440 --> 0:24:11.360 not just concerned about the wild rabbits but also sort 0:24:11.359 --> 0:24:14.240 of domestic pet owners. Is there anything good on the 0:24:14.240 --> 0:24:16.320 horazon or is there any good news on the horizon 0:24:16.359 --> 0:24:20.280 potentially for a vaccine or any sort of control, I 0:24:20.320 --> 0:24:23.280 guess either for both the wild rabbits or people who 0:24:23.320 --> 0:24:24.560 have domestic pets. 0:24:25.720 --> 0:24:30.320 Certainly for domestic pets, good news with RHDV or caliciviruses 0:24:30.400 --> 0:24:33.720 is that really there's only those two types, so RHDV 0:24:34.080 --> 0:24:38.400 one and then RHDV two, and the immunity induced if 0:24:38.400 --> 0:24:41.800 you do stuff I have infection or after vaccination is 0:24:42.000 --> 0:24:44.959 pretty much lifelong. Like it's really durable. It's a really 0:24:45.160 --> 0:24:50.200 strong induction of immunity. And so RHDV two vaccines have 0:24:50.320 --> 0:24:53.320