Moxidectin steady state prior to inoculation protects cats from subsequent, repeated infection with Dirofilaria immitis

Table 1 Numbers of Dirofilaria immitis recovered at necropsy, antigen test results, antibody test results, and significant histopathologic lesions consistent with heartworm infection in cats inoculated with D. immitis

			Pulmonary artery lesion score			Pulmonic trunk lesion score
Non-treated cats (No. *D. immitis* recovered)	Antigen*	Antibody*	Intima, thickening and villous proliferation	Intima, leukocyte infiltration	Media, thickening	Intima, thickening	Intima and adventitia, leukocyte infiltration
1 (0)**	NEG	POS	4	3	4	2	3
2 (6)	POS	POS	4	3	1	2	2
3 (1)	NEG	POS	4	4	4	4	3
4 (2)	NEG	POS	2	2	0	0	0
5 (1)	NEG	POS	4	4	3	0	0
6 (2)	NEG	POS	4	3	2	2	3
7 (0)	NEG	NEG	0	0	0	0	0
8 (0)	NEG	NEG	0	0	0	0	0
9 (0)	NEG	NEG	0	0	0	0	0
Treated
11 (0)	NEG	NEG	0	0	0	0	0
12 (0)	NEG	NEG	0	0	0	0	0
13 (0)	NEG	NEG	0	0	0	0	0
14 (0)	NEG	NEG	0	0	0	0	0
15 (0)	NEG	NEG	0	0	0	0	0
16 (0)	NEG	NEG	0	0	0	0	0
17 (0)	NEG	NEG	0	1	0	0	0
18 (0)	NEG	NEG	0	0	0	0	0
19 (0)	NEG	NEG	0	0	0	0	0
20 (0)	NEG	NEG	0	0	0	0	0

*Antigen and antibody results from cats 1–6 were published previously; 5/6 cats converted to antigen positive following heat treatment of serum to disrupt immune complexes [13]. None of the non-infected cats (cats 7–9, 11–20) converted to antigen positive with heat treatment (data not shown). **No worms were recovered but severe gross and histologic pulmonary lesions were present.
Treated cats received four monthly topical treatments with 10% imidacloprid-1% moxidectin prior to, but not after, inoculations; data provided were collected on study day 224. (Positive or significant results in bold).

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