Prime detection of Dirofilaria immitis: understanding the influence of blocked antigen on heartworm test performance

Table 6 Results of testing canine^a blood samples for antigen (Ag) of Dirofilaria immitis (Di) before and after heat pretreatment of samples and for microfilariae (MF) of D. immitis by modified Knott followed by morphological identification

Antigen test performed	Number (% positive)^b	Di Ag + Di MF + (%)	Di Ag + Di MF - (%)	Di Ag - Di MF + (%)	Di Ag - Di MF - (%)
Before heat	21/162 (13.0)	1 (0.6)	14 (8.6)	6 (3.7)^c	141 (87.0)^c
After heat	40/162 (24.7)	7 (4.3)^c	33 (20.4)^c	0 (0)	122 (75.3)^c

^aPet or shelter dogs, true heartworm status unknown
^bPositive for Dirofilaria immitis by at least one laboratory method
^cThree samples had microfilariae of Acanthocheilonema reconditum. The first contained both D. immitis and A. reconditum microfilariae and was negative before but positive after heat treatment. The second had only A. reconditum microfilariae and was negative before and negative after heat treatment. The third had only microfilariae of A. reconditum and was negative before and positive after heat treatment

ISSN: 1756-3305