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

Little SE, Hostetler JA, Thomas JE, Bailey KL, Barrett AW, Gruntmeir K, Gruntmeir J, Starkey LA, Basel C, Blagburn BL - Parasit Vectors (2015)

Bottom Line: Blood samples were collected from each cat from 1 month prior to treatment until 7 months after the final inoculation and tested for antibody to, and antigen and microfilaria of, D. immitis.Cats treated with topical 10% imidacloprid-1% moxidectin prior to trickle inoculation of D. immitis L3 larvae throughout the 28 day post-treatment period remained negative on antibody and antigen tests throughout the study and did not develop gross or histologic lesions characteristic of heartworm infection.Microfilariae were not detected at any time.

View Article: PubMed Central - PubMed

Affiliation: Department of Veterinary Pathobiology, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK, USA. susan.little@okstate.edu.

ABSTRACT

Background: Infection of cats with Dirofilaria immitis causes seroconversion on antibody tests and pulmonary pathology, often without subsequent development of adult heartworms. Consistent administration of topical 10% imidacloprid-1% moxidectin has been shown to result in sustained plasma levels of moxidectin in cats after three to five treatments, a pharmacokinetic behavior known as "steady state".

Methods: To evaluate the ability of moxidectin at "steady state" to protect cats from subsequent infection with D. immitis, cats (n = 10) were treated with the labeled dose of topical 10% imidacloprid-1% moxidectin for four monthly treatments. Each cat was inoculated with 25 third-stage larvae of D. immitis 7, 14, 21, and 28 days after the last treatment; non-treated cats (n = 9) were inoculated on the same days, serving as infection controls. Blood samples were collected from each cat from 1 month prior to treatment until 7 months after the final inoculation and tested for antibody to, and antigen and microfilaria of, D. immitis.

Results: Measurement of serum levels of moxidectin confirmed steady state in treated cats. Cats treated with topical 10% imidacloprid-1% moxidectin prior to trickle inoculation of D. immitis L3 larvae throughout the 28 day post-treatment period remained negative on antibody and antigen tests throughout the study and did not develop gross or histologic lesions characteristic of heartworm infection. A majority of non-treated cats tested antibody positive by 3-4 months post infection (6/9) and, after heat treatment, tested antigen positive by 6-7 months post-infection (5/9). Histologic lesions characteristic of D. immitis infection, including intimal and medial thickening of the pulmonary artery, were present in every cat with D. immitis antibodies (6/6), although adult D. immitis were confirmed in only 5/6 antibody-positive cats at necropsy. Microfilariae were not detected at any time.

Conclusions: Taken together, these data indicate that prior treatment with 10% imidacloprid-1% moxidectin protected cats from subsequent infection with D. immitis for 28 days, preventing both formation of a detectable antibody response and development of pulmonary lesions by either immature stages of D. immitis or young adult heartworms.

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Photomicrograph of hematoxylin & eosin-stained sections of lung. (a) Intimal thickening, villous proliferation and leukocyte infiltration of the pulmonary artery (arrow) associated with Dirofilaria immitis infection in a non-treated control cat (10× magnification). (b) Medial thickening of pulmonary artery branches (arrowheads) associated with Dirofilaria immitis infection in a non-treated control cat (20× magnification). (c, d) In cats treated with 10% imidacloprid-1% moxidectin prior to repeated inoculation with D. immitis, pulmonary lesions did not develop (10× and 20× magnification, respectively).
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Fig2: Photomicrograph of hematoxylin & eosin-stained sections of lung. (a) Intimal thickening, villous proliferation and leukocyte infiltration of the pulmonary artery (arrow) associated with Dirofilaria immitis infection in a non-treated control cat (10× magnification). (b) Medial thickening of pulmonary artery branches (arrowheads) associated with Dirofilaria immitis infection in a non-treated control cat (20× magnification). (c, d) In cats treated with 10% imidacloprid-1% moxidectin prior to repeated inoculation with D. immitis, pulmonary lesions did not develop (10× and 20× magnification, respectively).

Mentions: Microscopic examination of lung tissue of non-treated cats revealed significant thickening and villous proliferation of the intimal layer of the pulmonary artery (6/9 cats; mean severity score = 3.7; P = 0.133), leukocyte infiltration of the intimal layer of pulmonary artery (6/9 cats; mean severity score = 3.2; P = 0.133), and medial thickening of the pulmonary artery (5/9 cats; mean severity score = 2.3; P = 0.434). Non-treated cats also had intimal thickening (4/9 cats; mean severity score = 1.7) and intimal and adventitial leukocyte infiltration (4/9 cats; mean severity score = 1.8) evident in the pulmonic trunk, although the assigned scores were not significantly different than those in the treated cats (P = 0.113). Similar lesions were not present in treated cats (Table 1, Figure 2). No significant lesions were present in the kidney of any cats in this study. Numbers of nematodes, antigen test results, antibody test results, and significant histopathologic lesions consistent with D. immitis infection according to cat number are provided in Table 1.Table 1


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

Little SE, Hostetler JA, Thomas JE, Bailey KL, Barrett AW, Gruntmeir K, Gruntmeir J, Starkey LA, Basel C, Blagburn BL - Parasit Vectors (2015)

Photomicrograph of hematoxylin & eosin-stained sections of lung. (a) Intimal thickening, villous proliferation and leukocyte infiltration of the pulmonary artery (arrow) associated with Dirofilaria immitis infection in a non-treated control cat (10× magnification). (b) Medial thickening of pulmonary artery branches (arrowheads) associated with Dirofilaria immitis infection in a non-treated control cat (20× magnification). (c, d) In cats treated with 10% imidacloprid-1% moxidectin prior to repeated inoculation with D. immitis, pulmonary lesions did not develop (10× and 20× magnification, respectively).
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4340871&req=5

Fig2: Photomicrograph of hematoxylin & eosin-stained sections of lung. (a) Intimal thickening, villous proliferation and leukocyte infiltration of the pulmonary artery (arrow) associated with Dirofilaria immitis infection in a non-treated control cat (10× magnification). (b) Medial thickening of pulmonary artery branches (arrowheads) associated with Dirofilaria immitis infection in a non-treated control cat (20× magnification). (c, d) In cats treated with 10% imidacloprid-1% moxidectin prior to repeated inoculation with D. immitis, pulmonary lesions did not develop (10× and 20× magnification, respectively).
Mentions: Microscopic examination of lung tissue of non-treated cats revealed significant thickening and villous proliferation of the intimal layer of the pulmonary artery (6/9 cats; mean severity score = 3.7; P = 0.133), leukocyte infiltration of the intimal layer of pulmonary artery (6/9 cats; mean severity score = 3.2; P = 0.133), and medial thickening of the pulmonary artery (5/9 cats; mean severity score = 2.3; P = 0.434). Non-treated cats also had intimal thickening (4/9 cats; mean severity score = 1.7) and intimal and adventitial leukocyte infiltration (4/9 cats; mean severity score = 1.8) evident in the pulmonic trunk, although the assigned scores were not significantly different than those in the treated cats (P = 0.113). Similar lesions were not present in treated cats (Table 1, Figure 2). No significant lesions were present in the kidney of any cats in this study. Numbers of nematodes, antigen test results, antibody test results, and significant histopathologic lesions consistent with D. immitis infection according to cat number are provided in Table 1.Table 1

Bottom Line: Blood samples were collected from each cat from 1 month prior to treatment until 7 months after the final inoculation and tested for antibody to, and antigen and microfilaria of, D. immitis.Cats treated with topical 10% imidacloprid-1% moxidectin prior to trickle inoculation of D. immitis L3 larvae throughout the 28 day post-treatment period remained negative on antibody and antigen tests throughout the study and did not develop gross or histologic lesions characteristic of heartworm infection.Microfilariae were not detected at any time.

View Article: PubMed Central - PubMed

Affiliation: Department of Veterinary Pathobiology, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, OK, USA. susan.little@okstate.edu.

ABSTRACT

Background: Infection of cats with Dirofilaria immitis causes seroconversion on antibody tests and pulmonary pathology, often without subsequent development of adult heartworms. Consistent administration of topical 10% imidacloprid-1% moxidectin has been shown to result in sustained plasma levels of moxidectin in cats after three to five treatments, a pharmacokinetic behavior known as "steady state".

Methods: To evaluate the ability of moxidectin at "steady state" to protect cats from subsequent infection with D. immitis, cats (n = 10) were treated with the labeled dose of topical 10% imidacloprid-1% moxidectin for four monthly treatments. Each cat was inoculated with 25 third-stage larvae of D. immitis 7, 14, 21, and 28 days after the last treatment; non-treated cats (n = 9) were inoculated on the same days, serving as infection controls. Blood samples were collected from each cat from 1 month prior to treatment until 7 months after the final inoculation and tested for antibody to, and antigen and microfilaria of, D. immitis.

Results: Measurement of serum levels of moxidectin confirmed steady state in treated cats. Cats treated with topical 10% imidacloprid-1% moxidectin prior to trickle inoculation of D. immitis L3 larvae throughout the 28 day post-treatment period remained negative on antibody and antigen tests throughout the study and did not develop gross or histologic lesions characteristic of heartworm infection. A majority of non-treated cats tested antibody positive by 3-4 months post infection (6/9) and, after heat treatment, tested antigen positive by 6-7 months post-infection (5/9). Histologic lesions characteristic of D. immitis infection, including intimal and medial thickening of the pulmonary artery, were present in every cat with D. immitis antibodies (6/6), although adult D. immitis were confirmed in only 5/6 antibody-positive cats at necropsy. Microfilariae were not detected at any time.

Conclusions: Taken together, these data indicate that prior treatment with 10% imidacloprid-1% moxidectin protected cats from subsequent infection with D. immitis for 28 days, preventing both formation of a detectable antibody response and development of pulmonary lesions by either immature stages of D. immitis or young adult heartworms.

Show MeSH
Related in: MedlinePlus