The way parvovirus in dogs (PCV) works is that its multiplication will continue to generate new versions of itself at an even faster rate than its original form (host). Studies show that the reason for an extremely high rate of new mutations is the fact that viruses will easily and quickly adapt to their new hosts. This new study has taken a systematic analysis approach of the host range of parvovirus in dogs, and has demonstrated a variety of factors that will determine which canines and other carnivores can the virus continue to infect.
To define the natural host range of viruses related to CPV and FPV, Andrew Allison, from Cornell University in Ithaca, USA, and colleagues tested samples from over 850 individual wild carnivores from 18 species , including foxes, coyotes, raccoons, otters, martens, wolves, bobcats, and pumas, for the presence of parvoviruses, as the study analysis on ScienceDaily shows.
The results of this analysis has shown that these viruses were much more widespread in North American carnivores than previously thought. In addition, infection in some species such as coyotes and raccoons was very common, making it likely that transmission occurs not just sporadically from domestic animals but also between wild animals, and possibly between many different wild species.
Then to further explore how these parvo viruses adapt to alternative hosts, the researchers selected three different parvovirus in dogs variants (one isolated from domestic dogs and two from raccoons) and infected cultured cells from six different carnivore host species (domestic dog, domestic cat, domestic ferret, American mink, gray fox, and raccoon). They then allowed the viruses to multiply over several rounds of cell culture infection for 20 weeks (likely over 100 viral generations), then characterized any genetic changes that occurred after these passages, and compared them to the sequences of viruses recovered from hosts in the wild. The rationale was that mutations that are consistently associated with specific hosts in both natural systems and after experimental cell passage are likely to influence host range.
Canine Parvovirus study
Parvovirus in dogs, or canine parvovirus (CPV) first appeared as a new and highly widespread pathogenic disease in domestic dogs back in 70s. This virus is very closely related to feline panleukopenia virus (FPV), a type of parvovirus in cats and as well as other related carnivores roaming our planet today, as outlined in the study materials on PLOS.
Even though both of these dangerous infections have highly wide host ranges, this new study’s systematic analysis of that looked into viral sequences of canine parvovirus recovered from different wild carnivore species, as can be visible in the study, shown that even more than 95 percent were derived from CPV-like viruses, which automatically suggests that canine parvo is dominant in sylvatic cycles. Multiple other similar viral sequences demonstrated host-specific mutations in their capsid proteins, which were often close to sites known to control binding to the transferrin receptor (TfR), the host receptor for these carnivore parvoviruses, and which exhibited frequent parallel evolution.
Now to further examine the process of host adaptation, researchers have passaged parvoviruses with alternative backgrounds in cells from different carnivore hosts. Specific mutations were selected in several viruses and these differed depending on both the background of the virus and the host cells in which they were passaged. Strikingly, these in vitro mutations recapitulated many specific changes seen in viruses from natural populations, strongly suggesting they are host adaptive, and which were shown to result in fitness advantages over their parental virus.
Comparison of the sequences of the transferrin receptors of the different carnivore species demonstrated that many mutations occurred in and around the apical domain where the virus binds, indicating that viral variants were likely selected through their fit to receptor structures. Some of the viruses accumulated high levels of variation upon passage in alternative hosts, while others could infect multiple different hosts with no or only a few additional mutations.
Overall, these studies demonstrate that the evolutionary history of a virus, including how long it has been circulating and in which hosts, as well as its phylogenetic background, has a profound effect on determining viral host range.
Conclusions of the study
The researchers conclude that “parvoviruses may cross species barriers to infect less susceptible hosts through single or only a few mutations, and that differences in the genetic background, host range, and/or evolutionary history of the viruses influence their propensity to jump hosts.” Overall, they say, their findings “will help reveal the mechanisms that control host switching and viral emergence.
And in general, these studies demonstrate that the evolutionary history of a virus, including how long it has been circulating and in which hosts, as well as its phylogenetic background, has a profound effect on determining viral host range.
- Andrew B. Allison, Dennis J. Kohler, Alicia Ortega, Elizabeth A. Hoover, Daniel M. Grove, Edward C. Holmes, Colin R. Parrish. Host-Specific Parvovirus Evolution in Nature Is Recapitulated by In Vitro Adaptation to Different Carnivore Species. PLoS Pathogens, 2014; 10 (11): e1004475 doi: 10.1371/journal.ppat.1004475