Recombination Between Vaccine and Field Strains of Canine Parvovirus is Revealed by Isolation of Virus in Canine and Feline Cell Cultures

Abstract

ABSTRACT. Canine parvovirus type 2 (CPV) is a pathogen that causes severe hemorrhagic gastroenteritis with a high fatality rate in pups worldwide. Since CPV emerged in the late 1970s, its origin has been explored with the conclusion that CPV originated from feline panleukopenia virus or a closely related virus. Both high mutation rate and recombination are assumed to be key factors in the evolution of parvoviruses. Here we provide evidence for natural recombination in CPV isolated from dogs in cell culture. Antigenic and genetic properties of isolates from 10 diseased pups were elucidated. Six pups had been vaccinated beforehand with live combined vaccine containing original antigenic type CPV (CPV-2). Six isolates recovered from 4 vaccinated pups in cell cultures were found to contain either CPV-2 or CPV-2-like viruses. The other isolates, including all those from non-vaccinated pups, were CPV-2b viruses. Antigenic typing of two CPV-2-like isolates, 03-029/M and 1887/f, with a monoclonal antibody panel suggested they were a mixture of CPV-2 and CPV2a (03-029/M) and a recombinant of CPV-2 and CPV-2b (1887/f). Genetic analysis of the VP1 gene indicated that isolate 03-029/M was a mixture of CPV-2, CPV-2a and a recombinant of CPV-2 and CPV-2a viruses, while isolate 1887/f was composed of a recombinant of CPV-2 and CPV-2b viruses. This is the first demonstration of natural CPV recombination in the field and suggests that recombination in the evolution of CPV is a more frequent and important process than previously believed. KEY WORDS: canine parvovirus, cell culture, dog, parvovirus, recombination.J. Vet. Med. Sci. 70(12): 1305-1314 Canine parvovirus type 2 (CPV), one of the feline parvovirus (FPV) subspecies, emerged suddenly throughout the world in the late 1970s as a new pathogen that caused severe hemorrhagic gastroenteritis and myocarditis in domestic dogs [1,2,7,20,23,40]. Mortality rate is usually high, particularly in non-immune pups. The origin of the virus is still not clear but the most likely hypothesis from phylogenetic analysis is that CPV originated from feline panleukopenia virus (FPLV) or a very closely related carnivore parvovirus of feral canids, such as foxes and mink [52,55]. There has been speculation that, during circulation for some time in an European local dog population, this ancestral CPV gradually adapted for domestic dogs and the emergent original CPV (antigenic type 2: CPV-2) rapidly spread globally as a new pathogen of domestic dogs.In the early 1980s, this first CPV-2 disappeared from the field having been replaced by a new antigenic variant designated CPV-2a, and another antigenic variant CPV-2b appeared soon afterwards. These variants can be distinguished by monoclonal antibodies (MAbs) [35,43,[45][46][47]. CPV-2a and 2b use both canine and feline transferrin receptors for binding to cells both in vitro and in vivo [17,42] and consequently can infect dogs as well as cats [34,56]. In contrast, CPV-2 can infect both feline and canine cells in vitro but infects only dogs in vivo [57]...

Evidence for Recombination Between Feline Panleukopenia Virus and Canine Parvovirus Type 2

“…The XJ-1 strain may be the first recombinant resulting from a crossspecies infection. We believe that the inter-FPV subspecies recombination revealed in the present study, together with the inter-antigenic recombination of CPV recently reported in vaccinated pups [20], should be considered as mechanisms for both the emergence of CPV and the evolution of parvoviruses in nature, in addition to the previous "high mutation & positive selection" theory [32].…”

“…More recently, we provided the first clear evidence of recombination events between CPV antigenic types in natural conditions: that is, between vaccine CPV-2 and field CPV-2a, and vaccine CPV-2 and field CPV-2b viruses, in dogs vaccinated with live combined vaccine containing CPV-2 [20]. These results suggested that recombination is a more frequent event than previously believed for the FPV subspecies that generally cause acute infection.…”

“…However, over a long period of time no evidence was forthcoming for recombination events among FPV subspecies until our previous study [20] which demonstrated for the first time inter-antigenic type recombinants between CPV-2, CPV-2a, and CPV-2b, found in pups vaccinated with live combined vaccine immediately before developing parvovirus-induced disease. The recombinants were detected in two of six vaccinated pups but none of four unvaccinated pups, suggesting they were recombinants between the vaccine CPV-2 and either field CPV-2a or 2b, because only antigenic type CPV-2 has been included in canine vaccine products in Japan since 1984 [34].…”

Parvoviruses evolution in carnivores

“…XX w. opracowano różne rodzaje szczepionek przeciw chorobom wywołanym przez FPV. Pierwsze szczepionki przeciw chorobom wywołanym przez MEV, CPV opracowano w kilkanaście lat po wystąpieniu pierwszych ognisk chorobowych (24,25,37). Szczepionki te są także stosowane w immunizacji dzikich zwierząt mięsożer-nych i wydają się dla nich bezpieczne oraz skutecznie chronią przed wystąpieniem choroby.…”

“…Istnieje podejrzenie, że u ko-tów zakażonych CPV, podobnie jak u psów, występują czasami równoczesne zakażenia lokalnymi szczepami oraz wirusami szczepionkowymi (25). Populacja wirusa jest właściwie homogenna, a źródłem zmienności są głównie zakażenia mieszane FPV oraz CPV, co znajduje potwierdzenie w zakażeniu mieszanym in vivo FPV i CPV (39).…”