PhD Thesis Demeter Zoltan

Today a very diverse distribution of types 2a, 2b and 2c can be observed in most
European countries (Decaro et al., 2007a), and there is evidence that the newest
genotypes tend to replace previous variants (Martella et al., 2004; 2005; Decaro et al.,
2007a). This replacement has been associated with increased ability to bind to canine
transferrin receptors, although it might not rule out the possibility of mutations at
residue 426 of the VP2 protein being selected also for their antigenic effects (Truyen,
2006; Decaro et al., 2007a).
CPV2 infections have been reported in several species, such as domestic dogs,
bush dogs (Speothos venaticus), coyotes (Canis latrans), maned wolves (Chrysocyon
brachyurus) and crab-eating foxes (Cerdocyon thous), but it can be assumed that most if
not all Canidae are susceptible (McCaw & Hoskins, 2006). The original CPV2 isolates
infected only dogs, whereas the newer genotypes (2a, 2b) can also infect cats
experimentally and naturally as well (Parrish et al., 1988; McCaw & Hoskins, 2006).
Not all infected animals develop clinical signs. Clinical illness however is most
severe in young, rapidly growing puppies with concurrent parasitic infestation and/or
bacterial, viral infections. In susceptible populations, the incidence of severe disease and
death can be very high (McCaw & Hoskins, 2006).
CPV2 is highly contagious and most infections occur as a result of contact with
contaminated feces in the environment or fomites. Previous observations have
demonstrated that the infectious virus survives for at least one year in sandy or clay
soils (Greene & Schultz, 2006). The incubation period can vary among genotypes from
7 to 14 days, but in field conditions in case of CPV2a and 2b it can be as brief as 4 to 6
days. Acute CPV2 infections can be seen in dogs of any breed, age or sex. Nevertheless,
pups between 6 weeks and 6 months of age, and some large breeds seem to have an
increased risk (McCaw & Hoskins, 2006).
3.3.2 Pathogenesis
Similarly to FPV, the pathogenesis of CPV2 is defined by the requirement for mitotic
cells, dividing lymphoid and intestinal epithelial cells being the primary targets of the
virus (Parrish, 1995).
The site of virus entry and initial natural infection occurs through the cells of the
nasopharynx, the tonsils or other lymphoid tissues (Appel et al., 1979). Virus is isolated
between 1 and 3 days after the infection from the tonsils, retropharyngeal lymph nodes,
thymus and mesenteric lymph nodes, and after approximately 3 days virus is also
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