August and September… The Season for SSWD

Summer in Ithaca is usually a time for summer-ish things, like hiking and biking and walking and kayaking. We celebrate the sun being out, temperatures being warm, and the days being long. Because in a few months the sun will be hidden, the temperatures cold, and the days being shorter than business hours.

Summer is also the time for SSWD to occur on the west coast. And it has occurred, as predicted, in several places where we’d expected it to happen. Reports from Whidbey Island by Jan Kocian suggest that a stable, large population of several species of star crashed out in early August. Almost synchronously, the large and diverse population in Kodiak crashed dramatically. The large population in Unalaska persists. The wasting disease persists elsewhere at low levels; in some places there has been a strong recruitment of juveniles, in others they’re absent. In some places the juveniles are getting sick during summer, in others they are fine. The disease appears to correspond with elevated water temperature in some places, in others the opposite; it also corresponds with low tides at midday in some places, full moon in others. It’s an interesting mixture of environmental conditions which may lead to full-blown disease condition, but that exact mixture still eludes us.

buoydata

Temperature data from the Friday Harbor Data Buoy, National Data Buoy Center, NOAA (http://www.ndbc.noaa.gov/station_history.php?station=frdw1). Note the warmer-than-usual winter temperatures in 2015 and 2016.

What’s fascinating is that we have been holding onto sea stars in our aquarium facility for 5 months from these same locations, and they are showing few if any signs of disease. They’ve had a bunch of different ‘insults’ (meaning perturbations of environmental conditions) thrown their way in recent months. The facility warmed up for several hours by several tens of degrees F when the A/C failed on one of the hottest Ithaca days, before going back down to temperature. Those stars are fine. Several stars were subject to toxic ammonium conditions, high turbidity, and were more or less moribund after an attempted experiment. They are fine now. Animals have been poked and prodded, even chunks taken out of their arms. They are fine. And, interestingly, we do seem to have SSaDV in a small number of our stars (and in super low loads), but they don’t seem to be developing any disease. It’s clear that the disease requires a confluence of different factors both microbial and environmental to occur to elicit an epidemic. It’s also clear that sea stars are incredibly robust animals that can resist a wide variety of insults.

Animals were subject to several insults; high NH4+, high temperature, we even tried to fistulate a sea star (right) so that we could observe it’s internal anatomy during transmission experiments. The animal ditched its cannula after 3 days and its fine. Animals also spawned because of NH4+ stress (left is a photo of sea star gametes), and the animals almost died. But they are fine now.

For the last couple of months the team has been following the disease outbreaks while we focus on both lab-based approaches. Elliot’s been focused on examining a new virus discovered on the east coast of the US. Early reports this summer came in of sea stars with disease signs, including lesions, protruding organs, etc. In August, Elliot traveled to Shoals Marine Lab, Cornell and the University of New Hampshire’s undergraduate teaching lab in the Gulf of Maine to collect symptomatic and asymptomatic animals; we have also been working with the Ocean Genome Legacy, New England Aquarium and Mystic Aquarium on their animals. The East Coast wasting disease has affected populations periodically for at least the last 40 years. A scientific collector in Bar Harbor, ME, said that they see this kind of disease every 10 – 20 years. In 2015, we were contacted by public aquaria that sea stars in their collections were being affected by wasting with almost the same progression we’d heard about in 2013 on the Pacific coast. Interestingly, Ian was in Boston for a hockey tournament in mid-August and while off the ice went to the New England Aquarium for a look. Save for a couple of Patirias and a few Asterias forbesii in their touch tanks, sea stars were indeed very sparse. We will see whether this new virus is associated with east coast wasting.

EastCoastStar.png

Asterias rubrens from Shoals Marine Lab (photo credit = Jim Coyer).

Few sea stars were in the New England Aquarium tanks…

Meanwhile, Jacob and Mitch have been busy finishing off analyses of samples collected during the January research cruise in the Puget Sound. We collected over 300 samples during the cruise, and it’s taken quite a while to get through them. However, their analysis has reached an end and soon we will be able to describe the geographic distribution of SSaDV publicly.

Ian has also been back in the lab following a summer of workshops, conferences, teaching development, and hockey. The conferences over the summer gave him some new ideas about how SSaDV might transmit and appear well correlated to the disease in some places but poorly in others. Viruses do not behave the same as bacteria when it comes to environmental conditions, for the most part. As non-living entities, they have no metabolism but rely on their hosts to make new copies of themselves. However, virus particles themselves are subject to environmental conditions that may enhance their production and decay, which in turn may influence their spread and infectivity. Because SSaDV isn’t yet cultivated (there are no echinoderm cell lines…), this demands either selective purification of the virus away from other viruses and cell materials, which is problematic since many things from cells are in the same size and weight range as viruses. Or, it is possible to take components of the virus, for example it’s capsid (the bit that makes the icoscohedral head of the virus), and make synthetic copies in the lab then work with those. Ian’s been working on these two approaches, which will hopefully allow the team to study how viruses behave in water and consequently how they may spread.

Sucrose gradient ultracentrifugation (left) has yielded slightly purified SSaDV, but this has proved incompatible with electron microscopy. Meanwhile Ian’s been busy preparing synthetic proteins via in vitro translation of SSaDV’s capsid protein (right). It’s a new frontier for the team, since Ian has never worked with proteins before!

So a busy time for the lab to be sure. What does the future hold? We are going to be doing more transmission experiments (we have new clues as to how SSaDV may be transmitted), and of course work in the lab to understand SSaDV’s persistence. We’ll also continue to track populations of sea stars – notably the one in Dutch Harbor – and see when they collapse. We also seek to understand the biogeographic variation of sea star associated densoviruses, since they seem to be a common constituent of sea stars worldwide, yet in only few populations are they actually deleterious.

 

 


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