False negative antigen tests in dogs infected with heartworm and placed on macrocyclic lactone preventives

Parasites & Vectors

Table 1 Prescribed preventive, administration route, compliance, doxycycline use, and results of modified Knott test and antigen tests on samples collected from 15 heartworm infected dogs managed with slow kill

Dog ID	Preventive prescribed	Route of administration	Compliant with dispensing	Doxycycline (10 mg/kg PO) protocol	Modified Knott	Pre-heating antigen test results	Post-heating antigen test results
1	Moxidectin	Topical	No	30d	ND	-	+
2	Moxidectin	Topical	Yes	30d, four times	ND	-	+
3	Moxidectin	Topical	No	30d, four times	ND	-	+
4	Ivermectin	Oral	Yes	30d, twice	Neg	-	+
5	Ivermectin	Oral	No	30d	Neg	-	+
6	Ivermectin	Oral	No	30d, twice	Neg	-	+
7	Ivermectin	Oral	Yes	30d, twice	Neg	-	+
8	Ivermectin	Oral	No	30d	POS*	-	+
9	Moxidectin	Topical	Yes	6mo	ND	-	-
10	Moxidectin	Topical	No	30d, twice	Neg	-	-
11	Ivermectin	Oral	Yes	30d	Neg	-	-
12	Ivermectin	Oral	Yes	30d, twice	Neg	-	-
13	Ivermectin	Oral	No	30d	ND	-	-
14	Ivermectin,	Oral	Yes	30d, twice	ND	-	-
	Milbemycin	Oral
15	Ivermectin,	Oral	No	30d, three times	Neg	-	-
	Milbemycin	Oral

*Identity of microfilariae confirmed as Dirofilaria immitis by morphology and by PCR and sequencing.
ND = Not Done.

ISSN: 1756-3305