Transrectal Selamectin to Eliminate Nasal Mites (Halarachne miroungae) in Sea Otters (Enhydra lutris)
IAAAM 2009
Steven R. Brown; Eric N. Brown
Animal Medical Care of Newport, PC, Newport, OR, USA

Abstract

A preliminary study was conducted with four male sea otters (Enhydra lutris) from the Oregon Coast Aquarium to determine the efficacy and safety of selamectin to eliminate nasal mites. Two of the sea otters were E.l. kenyoni and two were E.l. nereis, with ages ranging from 9 to 18 years. Previous physical exams had confirmed the presence of nasal mites in these patients even though they showed no clinical signs at the time of the study.

Selamectin [Revolution® (Pfizer)] is a transdermal form of selamectin that has been shown to be effective in the elimination of skin and ear mites in some terrestrial species,3 including dogs and cats. The recommended application site of the product is on the skin on the dorsum of the neck, where it is subsequently absorbed, concentrating in the sebaceous oil glands of the skin.2 Due to the very dense hair coat in sea otters, it was unknown whether skin application and transdermal absorption would be effective in reaching therapeutic drug concentrations. The concept of applying selamectin in the otter's ear canal was quickly abandoned due to the difficulty to achieve adequate safe physical restraint of the head without sedation. Since many medications are well tolerated and absorbed from the rectal mucosa,1 it was postulated that selamectin could be administered by this method. In the course of this study, we found that the product could be easily infused into the rectum of a sea otter restrained with a "push bag" in a "V" trough box.

For this trial each of the sea otters were sedated with medetomidine [Domitor® (Pfizer)] at 0.034 mg/kg IM, with subsequent intubation and maintenance at 2% isoflurane. Blood collection was done for chemistry and CBC profile (Table 1) prior to administration of selamectin. An otoscope with operating head (Welch Allyn) was used for visual assessment of the mite population within each nostril (Table 1). After nasal scoping, 2 ml of selamectin (240 mg total dose, dosage 6.4-8.14 mg/ml) was administered rectally using a pliable teat cannula and 3 ml syringe. Subsequent rectal administration of selamectin was performed using physical restraint with a "push bag" by the aquarium staff at two week intervals for a total of six doses. Blood collection and nasal scoping were repeated with the above noted chemical restraint at week 6 and 14 (2 weeks after selamectin) of the study. Rectal administration of selamectin was performed using physical restraint with a "push bag" by the aquarium staff at 2 week intervals for a total of 6 doses. At the final scoping, zero mites were noted in the four sea otters.

Selamectin is a semi-synthetic avermectin. Similar to other chemicals in this classification, its activity is believed to be due to enhanced chloride permeability or enhancing the release of gamma amino butyric acid (GABA) at presynaptic neurons. Reported adverse effects in mammals have included anorexia, vomiting, diarrhea, muscle tremors, ataxia, tachypnea and seizures.2 None of these effects were observed in the study group.

This study supports the use of transrectal selamectin, as a treatment for nasal mites in sea otters. Based upon the study animals' clinical responses after transrectal administration of the drug, selamectin appears to be effectively absorbed through the mucosa of the rectum. No evidence of systemic selamectin toxicity was noted in sea otters in this trial. Further study of pharmacodynamics is recommended for this product in this species.

Table 1a. Body weights, nasal mite counts, and blood values of sea otters treated with selamectin.

Animal Name

Aialik

Hunter

Date Of Birth

June 1998

February 1998

Date Of Testing

9/11/2007

10/23/2007

12/11/2007

9/13/2007

10/25/2007

12/13/2007

Weight (Kg)

36.36

37.72

37.5

29.55

30.91

30.91

Mites In Left Nostril

60+

1

0

0

1

0

Mites In Right Nostril

60+

0

0

25

0

0

ALB (g/dL)

2.7

3.1

2.8

2.8

2.7

4.2

ALP (U/L)

56

70

77

70

85

95

ALT (U/L)

276

377

254

364

474

445

AMY (U/L)

<5

<5

<5

<5

<5

<5

TBIL (mg/dl)

0.2

0.4

0.3

0.2

0.4

0.4

BUN (mg/dL)

44

48

49

54

61

64

Ca++ (mg/dL)

8.8

9.6

9.0

8.7

9.3

8.9

PHOS (mg/dL)

5.7

4.9

5.8

5.3

4.7

6.3

Cre (mg/dL)

0.3

0.4

0.2

0.5

0.4

0.7

Glu (mg/dL)

104

105

96

118

95

91

Na+ (mmol/L)

159

153

158

157

159

153

K+ (mmol/L)

4.0

4.

4.3

4.0

3.7

4.3

TP (g/dL)

7.6

7.8

7.8

7.0

7.4

7.0

GLOB (g/dL)

4.9

4.7

5.0

4.2

4.7

2.8

WBC (103/mm^3)

5.0

6.0

6.6

6.4

6.3

6.1

RBC (106/mm^3)

4.61

4.52

5.37

5.02

5.07

5.66

HGB (G/Dl)

19.3

18.3

21.1

19.8

19.6

21.9

HCT (%)

52.9

51.4

60.9

55.2

56.2

62.2

PLT (103/mm^3)

362

394

401

321

219

250

MCV (m^3)

115

114

113

110

111

110

MCH (pg)

41.8

40.5

39.3

39.5

38.7

38.7

MCHC (g/dL)

36.4

35.6

34.7

35.9

34.9

35.2

RDW (%)

12.5

12.3

14.3

12.6

13.1

13.0

MPV (fl)

7.9

7.8

7.9

8.6

9.6

9.0

%LYM

17.3

12.9

13.5

24.1

22.1

20.3

%MON

3.1

3.0

2.5

3.3

3.5

3.7

%GRA

79.6

84.1

84.0

72.6

74.4

76.0

Table 1b. Body weights, nasal mite counts, and blood values of sea otters treated with selamectin (cont.).

Animal Name

Judge

Kodiak

Date Of Birth

June 2000

June 1989

Date Of Testing

9/11/2007

10/23/2007

12/11/2007

9/13/2007

10/25/2007

12/13/2007

Weight (Kg)

30.68

31.36

30.45

35.45

35.00

35.00

Mites In Left Nostril

75+

27

0

1

2

0

Mites In Right Nostril

75+

15

0

17

1

0

ALB (g/dL)

2.6

3.3

3.6

2.7

3.0

3.4

ALP (U/L)

63

73

86

51

60

72

ALT (U/L)

116

196

148

333

253

237

AMY (U/L)

<5

<5

<5

<5

<5

<5

TBIL (mg/dl)

0.3

0.4

0.3

0.3

0.4

0.4

BUN (mg/dL)

42

44

54

50

62

49

Ca++ (mg/dL)

8.9

9.2

9.0

8.4

8.7

8.5

PHOS (mg/dL)

3.8

4.8

5.4

3.7

5.6

5.9

Cre (mg/dL)

0.4

0.3

0.3

0.4

0.5

0.4

Glu (mg/dL)

122

122

104

103

180

145

Na+ (mmol/L)

154

149

159

156

151

155

K+ (mmol/L)

3.4

3.4

3.5

3.9

4.0

3.9

TP (g/dL)

7.0

7.2

7.1

7.1

7.4

8.0

GLOB (g/dL)

4.4

3.9

3.6

4.4

4.5

4.6

WBC (103/mm^3)

6.5

7.3

6.0

6.7

5.9

6.1

RBC (106/mm^3)

5.01

5.18

5.61

4.08

4.21

4.13

HGB (G/Dl)

19.8

19.9

21.3

15.9

16.6

15.9

HCT (%)

54.8

56.6

61.3

45.2

46.5

44.5

PLT (103/mm^3)

430

304

227

182

301

252

MCV (m^3)

109

109

109

111

111

108

MCH (pg)

39.6

38.5

38.0

39.1

39.5

38.4

MCHC (g/dL)

36.2

35.2

34.8

35.2

35.7

35.7

RDW (%)

12.6

12.3

13.2

11.9

12.4

11.7

MPV (fl)

8.1

8.6

9.1

9.8

9.9

9.5

%LYM

27.4

25.9

30.7

11.0

14.2

14.7

%MON

6.4

6.2

6.7

2.7

3.3

3.5

%GRA

66.2

67.9

62.6

86.3

82.5

81.8

Acknowledgements

Jay Docker and Eric White, Pfizer; Judy Tuttle and Marine Mammal staff, Oregon Coast Aquarium.

References

1.  Drugs.com. 1998. Rectasol-HC. [Date unavailable] from Drugs.com: http://www.drugs.com/mtm/rectasol-hc-cream-suppository.html

2.  Plumb D.C. 2005. Plumb's Veterinary Drug Handbook. Stockholm, Wisconsin: Pharma Vet Inc.

3.  Revolution® [package insert]. Exton, PA: Pfizer Animal Health.

 

Speaker Information
(click the speaker's name to view other papers and abstracts submitted by this speaker)

Steven R. Brown
Animal Medical Care of Newport, PC
Newport, OR, USA


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