Moreover,
there are still large areas in the world, especially in
Africa, where the prevalence of canine dirofilaria infection is largely unknown. Therefore, screening for
dirofilaria infection in dog populations throughout the
world is relevant, not only to avoid international dissemination
by the importation of pathogens but also to
implement national dirofilariasis control measurements.
Such screening can be achieved by the detection
of microfilariae, antigen testing (commercial kits
available only for D immitis), or by molecular biology
methods. Microfilaria screening may not be as sensitive
as antigen testing, as shown in a study in which
20% of dogs were falsely negative. However, microfi-
laria observation is important, not only because it validates
serologic test results but also because it identifies
dogs serving as a reservoir, thus alerting veterinarians
to potential adverse reactions when using microfilaricide
drugs. Currently, 2 methods are recommended
for microfilaria detection: membrane filtration and the
modified Knott’s test (MKT). The latter is the most
commonly used, being considered highly sensitive and
specific. Nevertheless, to the best of our knowledge,
only a single study compared it with the buffy coat
smear (BCS). The BCS has been accepted for many
years for the diagnosis of human filariasis
, but veterinary
studies have exclusively focused on the direct
observation of the (unbroken) microhematocrit tube
at low magnification disregarding the use of BCS.
Direct observation of hematocrit preparations proved
to be useful in microfilaria screening, but has inherent
limitations in species identification, as morphologic
details are difficult to assess