RETROSPECTIVE STUDIES

Copperhead (Agkistrodon contortrix) Envenomation of Dogs: 52 Cases (2004–2011) Jessica C. Pritchard, VMD, Adam J. Birkenheuer, PhD, DVM, Rita M. Hanel, DVM, Michael W. Wood, PhD, DVM

ABSTRACT Copperhead envenomation is common within the US, and no studies exist describing the clinical course of copperhead envenomation in dogs. Almost all treatment decisions regarding those bites are extrapolated from retrospective studies evaluating the clinical course of rattlesnake bites. Because copperheads and rattlesnakes produce venom with different potency, assumptions that treatment of the different envenomations should be similar may be incorrect. The purpose of this retrospective study was to evaluate the clinical course of copperhead envenomation in dogs and administered treatments. Medical records of 52 dogs treated for copperhead envenomation were reviewed, and owners were contacted regarding outcome. The most common clinical signs associated with copperhead envenomation included swelling, pain, and ecchymosis. Clinicopathological abnormalities (e.g., thrombocytopenia, elevated clotting times, leukocytosis) were mild, and red blood cell morphology changes and coagulopathies were rare. Most dogs were treated with antimicrobials, analgesics, and fluid therapy. No dogs in this study required the use of antivenin and all survived to discharge. This study found that the clinical course after copperhead envenomation is generally limited to local rather than systemic illness. Copperhead envenomation in dogs is largely self-limiting and responsive to supportive care with hospitalization for monitoring. (J Am Anim Hosp Assoc 2014; 50:338–344. DOI 10.5326/JAAHA-MS-6131)

Introduction

family Crotalidae contains mostly water, along with additional

In the US, there are .120 species of snakes, 20 of which are

enzymes and peptides, varying by snake genera.7 The Crotalidae

1

venomous. It has been estimated that as many as 150,000 dogs and 2

are divided into three genera, Crotalus (rattlesnakes), Sistrurus

cats are bitten by one of those venomous species each year. The

(pygmy rattlesnakes), and Agkistrodon (copperheads and mocca-

venomous snakes are divided into two families, the Elapidae (coral

sins), each with different venom characteristics. Based on lethal

snakes) and Crotalidae or pit vipers (rattlesnakes, moccasins, and

dose 50% calculations, rattlesnake venom is the most potent,

copperheads). Pit viper envenomation is a common hazard for dogs,

followed by moccasin and copperhead venom.1,2,8 There are sev-

especially in the southern US. The clinical course of pit viper en-

eral retrospective studies evaluating the clinical course of, and

venomation can range from local effects, such as bite site swelling

treatments associated with, rattlesnake envenomation in dogs.3,4

and tissue necrosis, to more serious effects, including coagulopathies,

However, no similar studies exist evaluating copperhead enven-

hypotension, myocardial damage, and death.3,4 Reported mor-

omation in dogs.

4,5

Pain at the bite site is im-

The copperhead (Agkistrodon contortrix) is found in North

mediate and usually followed quickly by swelling.6 Onset of the

America from as far north as New York, west to Oklahoma, and

more serious clinical signs may be delayed for hours.1,6

as far south as Mexico. Copperheads can be identified by a pale

tality rates range from 1 to 30%.

Clinical signs related to snakebites stem from trauma from the

tan base color overlaid with a series of dark brown, hourglass-

bite itself as well as venom contents. Venom from snakes in the

shaped crossbands. They are most frequently found in deciduous

From the Department of Clinical Sciences, North Carolina State College of Veterinary Medicine, Raleigh, NC.

PO, per os

Correspondence: [email protected] (M.W.)

338

JAAHA

|

50:5 Sep/Oct 2014

ª 2014 by American Animal Hospital Association

Copperhead Envenomation in 52 Dogs

forests, hibernating during the winter in rocky outcroppings. In

test results were recorded when performed (packed cell volume,

2009, copperhead bites to humans comprised 40% of all ven-

total solids, blood glucose, complete blood count, serum bio-

omous snakebite calls to American Poison Control Centers, more

chemical analysis, coagulation panel). Treatments administered in

than any other venomous snake in the US.9 Despite the prevalence

hospital, including pain control, antibiotics, sedation, and fluid

of copperhead snakebites in the US, the lack of information

therapy, were recorded. Additionally, medications and treatments

describing the clinical course of envenomation in dogs forces

prescribed to be given at home were also recorded. Outcome was

clinicians to extrapolate treatment decisions based on the small

recorded for each patient, as well as the bill total for the visit and

amount of evidence from human literature, studies on rattlesnake

total hospitalization time. Efforts were made to assess whether the

envenomation in dogs, and anecdotal evidence. Because little

patients either improved or worsened during their hospitalization

information is available to prognosticate what animals will de-

time given the information provided by the record. Owners were

velop more serious signs, hospitalization for supportive care,

contacted by either phone or e-mail as part of the study and were

continued monitoring, and repeated laboratory work are often

asked about their dog’s improvement at home after discharge,

recommended.

2,8

In North Carolina, up to 90% of snakebites to humans are

if the dog required follow-up medical care at another facility, and if the dog developed evidence of bite site necrosis.

from copperhead snakes, and that state has the highest incidence of copperhead bites per capita in the nation.10,11 Wake County,

Results

North Carolina, the region from which the cases for this study

Case Information

were selected, is home to primarily one venomous snake: the

During the study period, 52 dogs met the inclusion criteria. Twenty

11

copperhead. Given the limited population of venomous snakes

of 52 dogs (38%) had confirmed bites and 32 of 52 dogs (62%) had

in Wake County, it is an ideal location for performing a retro-

suspected bites. Dogs ranged in age from 6 mo to 15 yr, with

spective study describing the clinical course of copperhead enven-

a median age of 6 yr. Median body weight was 24.1 kg, ranging

omation in dogs and treatment measures.

from 5 to 55 kg. Twenty-seven breeds were represented, with the most common being Labrador retrievers (n ¼ 9), mixed-breed

Materials and Methods

dogs (n ¼ 7), golden retrievers (n ¼ 4), dachshunds (n ¼ 3), and

Case Selection

Jack Russell terriers (n ¼ 3). Castrated male dogs were most

The electronic discharge database of the North Carolina State

frequently presented (46%), followed by spayed females (36%),

University Veterinary Teaching Hospital from 2004 to 2011 was

males (12%), and females (6%). Bites were reported between

searched for medical records containing the terms, “snakebite,”

April and October, with 94% (49 of 52) occurring between May

“snake bite,” “envenomation,” “copperhead,” “copper head,”

and September. The exact time to presentation from suspected

“Crotalid,” and “Agkistrodon.” Criteria for inclusion included dogs

envenomation, rather than an estimate, was recorded for 32 of

residing in Wake County that presented within 12 hr of a sus-

52 dogs, with a median time of 60.5 min (range, 17–360 min).

pected copperhead bite and that had not previously been presented for medical treatment at another facility. Dogs were

Clinical Findings

categorized as “confirmed” if the owners either saw the copper-

The most common presenting complaint was snakebite in 42 of

head bite the dog or found the dog with fang marks and a snake

52 dogs (81%), followed by facial swelling in 3 of 52 dogs (6%)

nearby. “Suspected” cases were categorized as those in which an

and lameness in 2 of 52 dogs (4%). Thirty-four of 52 dogs (65%)

animal had at least one fang mark, clinical signs consistent with

were bitten in the face, followed by a forelimb in 10 of 52 dogs

snakebite, and a history compatible with the possibility of

(19%), and a hind limb in 6 of 52 dogs (12%). One dog was bitten

snakebite. A total of 52 cases met the inclusion criteria.

in two locations (face and forelimb) and another was bitten on the thorax. All 52 dogs (100%) had swelling at the bite site. Other

Medical Records Review

common local effects of envenomation included bleeding at the

For each dog, the signalment, presenting complaint, date of

bite site in 14 of 52 dogs (27%), bruising/ecchymosis in 14 of

presentation, vital parameters (temperature, pulse, and respira-

52 dogs (27%), petechiation at the bite site in 2 of 52 dogs (4%),

tion), weight, and clinical signs as described by the attending

and erythema at the bite site in 5 of 52 dogs (10%). Five of 52 dogs

clinician were recorded. A pain scoring system raging from 0 to 4

(10%) had the lymph nodes draining the bite site enlarged on

(0, no pain; 4, intractable pain) was used to assess discomfort in

palpation. Forty-nine of 52 dogs (94%) had evidence of only one

some patients and recorded when available. Clinicopathological

bite (#2 puncture wounds), while the remaining 3 dogs (6%) had

JAAHA.ORG

339

evidence of more .1 bite (.2 puncture wounds). Of the dogs

reference range, 2.841–9.112 3 103/mL), decreased plasma pro-

that had an exact number of puncture wounds recorded (n ¼ 50),

tein in 7 of 38 dogs (18%), with a median plasma protein of

5 of 50 dogs (10%) had no visible puncture wounds despite the

6.6 g/dL (range, 4.5–7.8 g/dL; reference range, 6.1–7.5 g/dL),

owners seeing a snake strike their dogs and clinical signs consis-

nucleated red blood cells observed in 8 of 38 dogs (21%), and el-

tent with a snakebite. Thirteen of 50 dogs (26%) had one punc-

evated packed cell volume in 2 of 38 dogs (5%), with a median

ture wound, 31 of 50 dogs (62%) had two puncture wounds

packed cell volume of 51.5% (range, 26–64%; reference range, 39–

(constituting one bite), and 1 of 50 dogs (2%) had four puncture

58%). Only 1 of 38 dogs was listed as having echinocytes present.

wounds reported.

On serum biochemical evaluation, 4 of 29 dogs (14%) had elevated

On presentation, 49 dogs had vital signs (temperature, pulse,

total Ca values with a median value of 10.4 mg/dL (range, 9.6–

and respiration) recorded. Thirteen of 49 dogs (27%) were hy-

12.7 mg/dL). Five of 29 dogs (17%) were mildly hypokalemic.

perthermic (.39.28C), and 3 of 49 dogs (6%) were hypothermic

Mean serum potassium concentration was 4.6 mEq/L (range, 3.7–

(,37.78C). Twenty-six of 49 dogs (53%) were tachycardic (.120

5.7 mEq/L; reference range, 4.0–5.3 mEq/L) as shown in Table 1.

beats/min). One of 49 dogs (2%) was bradycardic (30 beats/min).

Twenty-eight dogs had prothrombin and activated partial

A pain scoring system assessed discomfort in 35 dogs on admis-

thromboplastin times evaluated on presentation. Only 1 of 28 dogs

sion. Of the dogs assigned a pain score, 2 of 35 dogs (6%) were

(3.5%) had a mild elevation in activated partial thromboplastin

given a 0, 4 of 35 dogs (11%) were given a 1, 15 of 35 dogs (43%)

(106 sec; reference range, 72–102 sec). None of the patients tested

were given a 2, 11 of 35 dogs (31%) were given a 3, and 3 of 35

had elevated prothrombin values.

dogs (9%) were given a 4. Of the dogs assessed to be the most painful, two of the three were bitten on the face, and the final dog

Antibiotics

was bitten on the thorax. There were no discernible differences in

Thirty-five of 52 dogs received antimicrobials while hospitalized.

clinically assessed vital parameters between dogs with confirmed

Thirty-one of 35 dogs (88%) received a combination penicillin

snakebites versus those with suspected snakebites.

b-lactamase inhibitor, either ampicillin Na/sulbactam Na in 25 of

Laboratory Findings

clavulanate potassium in 6 of 35 dogs (12.3–17.86 mg/kg per os

Results of initial complete blood count, reported in 38 dogs, in-

[PO] q 12 hr). Two of 35 dogs (6%) received cephalosporins

cluded thrombocytopenia in 9 of 38 dogs (24%) with a median

(22 mg/kg cefazolin IV q 8 hr), and 2 of 35 dogs (6%) received

platelet count of 229,000 platelets/mL (range 122,000–546,000;

fluoroquinolones (10 mg/kg ciprofloxacin IV q 24 hr). Forty-eight

reference range, 190,000–468,000/mL), leukocytosis in 10 of

of 52 dogs were sent home with antimicrobial therapy. Forty of

38 dogs (26%) with a median leukocyte count of 9.4 3 10 /mL

48 dogs (83%) received amoxicillin trihydrate/clavulanate potas-

(range, 3.6–23.7 3 103/mL; reference range, 4.39–11.6 3 103/mL),

sium (8.1–28.2 mg/kg PO q 12 hr), 6 of 48 dogs (13%) received

35 dogs (20–26.5 mg/kg IV q 8 hr) or amoxicillin trihydrate/

3

mature neutrophilia in 9 of 38 dogs (24%), with a median neu-

cephalexin (13.4–26.3 mg/kg PO q 12 hr), and 2 of 48 dogs (4%)

trophil count of 7.8 3 103/mL (range, 1.6–18.2 3 103/mL;

received ciprofloxacin (20 mg/kg PO q 24 hr).

TABLE 1 Abnormal Laboratory Findings in Dogs Bitten by Copperheads Clinical Abnormality (No. Assessed) Leukocytosis (38)

No. of Dogs ORR (%)

Median ORR

Range ORR

Median (All Dogs)*

Range (All Dogs)*

Reference Range

10 (26%)

13.6 3 103/mL

12.3–23.7 3 103/mL

9.4 3 103/mL

3.6–23.7 3 103/mL

4.39–11.6 3 103/mL

Thrombocytopenia (38)

9 (24%)

162,000/mL

122,000–185,000/mL

229,000/mL

122,000–546,000/mL

190,000–468,000/mL

Mature neutrophilia (38)

9 (24%)

11.8 3 103/mL

9.4–18.2 3 103/mL

7.8 3 103/mL

1.6–18.2 3 103/mL

2.8–9.1 3 103/mL

Nucleated red blood cells (38)

8 (21%)

1.5/100 WBC

1–5/100 WBC

—

—

—

Low plasma protein (38)

7 (18%)

6 g/dL

4.5–6 g/dL

6.6 g/dL

4.5–7.8 g/dL

6.1–7.5 g/dL

Hypokalemia (29)

5 (17%)

3.8 mEq/L

3.7–3.8 mEq/L

4.6 mEq/L

3.7–5.7 mEq/L

4.0–5.3 mEq/L

Hypercalcemia (29) Increased packed cell volume (38)

4 (14%) 2 (5%)

12.1 mg/dL 62%

11.6–12.7 mg/dL 60–64%

10.4 mg/dL 51.50%

9.6–12.7 mg/dL 26–64%

9.3–11.5 mg/dL 39–58%

Echinocytes (38)

1 (3%)

—

—

—

—

—

*Median and range values for all dogs assessed in the study. ORR, out of the reference range; —, value was not calculated/reported.

340

JAAHA |

50:5 Sep/Oct 2014

Copperhead Envenomation in 52 Dogs

Glucocorticoids

Discussion

Nine of 52 dogs received a single IV dose of dexamethasone as part

In the veterinary literature, there is a lack of data describing the

of their treatment. Seven of those dogs were bitten on the face. The

clinicopathological characteristics of copperhead envenomation in

average dose was 0.5 mg/kg, ranging from 0.1 to 2.0 mg/kg. No

dogs. Almost all treatment decisions regarding those bites have

dogs were sent home with glucocorticoids.

been extrapolated from a few retrospective studies evaluating the clinical course of rattlesnake bites.3,4 Because copperheads and

Pain Control

rattlesnakes produce venom with different potency, assumptions

While hospitalized, 48 of 52 dogs (92%) received at least one

that the treatment of the different envenomations should be

analgesic. Twenty of 48 dogs (42%) received intermittent IV

similar may be incorrect.

hydromorphone boluses (0.05–0.1 mg/kg IV), 18 of 48 dogs

Similar to previous studies evaluating snakebites in dogs,

(38%) received fentanyl as an IV continuous rate infusion (2–6

in this retrospective study, most copperhead bites occurred be-

mg/kg/min IV), 9 of 48 dogs (19%) received buprenorphine

tween May and September.3,4 That was likely due to both the

(0.01–0.02 mg/kg IV q 6–12 hr), 4 of 48 dogs (8%) received

hibernation patterns of copperheads (that retreat to rocky dens

tramadol (2.8–4.1 mg/kg PO q 8–12 hr), and 2 of 48 dogs (4%)

from October through March) and seasonal changes resulting in

received carprofen (2.2–4 mg/kg PO q 12–24 hr). Forty-nine of

more humans and animals being outside (thus having an in-

52 dogs (94%) were prescribed at least one analgesic at dis-

creased chance of interaction with a copperhead). As seen in dogs

charge. Forty-one of 49 dogs (84%) received tramadol (1.3–5.7

with rattlesnake envenomation, the most common clinical signs

mg/kg PO q 8–12 hr), 10 of 49 dogs (20%) received carprofen

were swelling, puncture wounds, and bleeding or ecchymosis,

(1.6–3.6 mg/kg PO q 12 –24 hr), 5 of 49 dogs (10%) had fentanyl

with most of the bites occurring on the head or neck.3–5 Despite

transdermal patches placed, 5 of 49 dogs (10%) received

swelling in the head and neck area, no dogs struck by copperheads

meloxicam (0.08–0.1 mg/kg PO q 24 hr), and 1 of 49 dogs (2%)

had upper airway obstruction described in the medical record.

received buprenorphine (0.01 mg/kg PO q 8–12 hr).

However, of the nine dogs that were given single doses of corticosteroids in hospital, seven had bites to the face. In this study,

Other Treatments

five dogs had regional lymph node enlargement. That finding was

No dogs received antivenin, and no dogs required blood

unique to this study, but was not surprising given that venom

products. Eleven of 52 dogs (21%) received diphenhydramine

travels via lymphatics.8 In humans with copperhead envenoma-

(1–2.2 mg/kg intramuscularly q 1–8 hr). Three of 52 dogs (6%)

tion, the most common clinical signs are pain and swelling.10

received famotidine (0.4–0.5 mg/kg IV q 12 hr). Thirty-three

While pain is difficult to subjectively quantify in dogs, most dogs

of 52 dogs (63%) received IV fluids. Of those 26 dogs (79%)

that had a pain score recorded in the medical record were listed as

received maintenance rates (1.5–4 mL/kg/hr) of IV fluids

being at least minimally painful (a score of $1) and the majority

while hospitalized. Six of 52 dogs (11%) were judged to be

of dogs were given analgesics while hospitalized.

hypovolemic and received either a fluid bolus and maintenance

A retrospective study looking at 31 dogs bitten by Eastern

rates of IV fluids or maintenance and replacement rates of IV

diamondback rattlesnakes found 42% developed cardiac arrhyth-

fluids.

mias, while another retrospective study of 100 dogs bitten by prairie rattlesnakes found that those dogs were often hypovolemic and

Outcome

required IV fluid resuscitation.3,4 In contrast, the majority of dogs

All dogs survived to discharge. The median hospitalization time

in this study did not require fluid therapy beyond maintenance

was 14.8 hr (range, 63 min to 48.9 hr). The median cost was

and none had reported cardiac arrhythmias other than sinus

$539.50 (range, $119.40–1283.50). Owner follow-up through re-

tachycardia based on auscultation at admission.

sponse to phone or e-mail survey was available for 27 of 52 dogs

Three studies of rattlesnake envenomation in dogs have re-

(52%). Tissue necrosis at the bite site was reported by 3 of

ported varying degrees of thrombocytopenia (88%, 81%, and 35%,

27 owners (11%). Of those, only one required follow-up care at

respectively) and coagulation abnormalities requiring blood

another veterinary facility and resolved with antibiotic treatment

product administration in (4%, 12%, and 35%, respectively).3–5

without the need for surgical debridement. Self-limiting infection

While almost one-quarter of dogs bitten by copperheads that

at the bite site was reported by 1 of 27 owners (4%) that did not

had platelet numbers assessed were thrombocytopenic, eleva-

require either follow-up treatment at an additional veterinary

tion in prothrombin time or partial thromboplastin time was

facility or changes in treatment protocol.

a rare finding and none of the patients required blood product

JAAHA.ORG

341

administration. That observation was unexpected because cop-

involves analgesia and antibiotics. In rare cases, antivenin, blood

perhead venom contains fibrolase, a known anticoagulant.12,13

products, and surgical wound management are needed.10 One

There are other components of venom that differ between rat-

study of management of copperhead snakebites in humans

tlesnakes and copperheads, such as crotalocytin (a serine protease

recommended withholding antivenin based on the belief and

in timber rattlesnake venom that causes platelet aggregation in

experience that copperhead envenomation in humans is largely

vitro) and crovidisin in prairie rattlesnake venom (that prevents

a self-limiting event.19

8

platelets from interacting with collagen, resulting in bleeding). A

Few dogs received glucocorticoids as part of their treatment.

lack of those components in copperhead venom, and other dif-

Glucocorticoid use in snakebites is controversial. More recent studies

ferences in venom fraction composition, may explain the differ-

have largely shown either no harm or benefit to the use of steroids in

ences between copperheads and other snakebites in terms of

envenomation in dogs.3,5 However, previous studies have shown

clinically assessable bleeding and coagulation abnormalities.12,13

mixed results, with some showing potential deleterious effects of

Echinocytosis has frequently been associated with snake

steroids when given to envenomated rodents and showing a possi-

envenomation in dogs and in one study of prairie rattlesnake

ble protective effect against death due to envenomation.20,21 Con-

envenomation echinocytosis was seen in 92% of dogs evalu-

cerns are also raised about impairment of tissue healing after

2,4,8,14

ated.

Only one dog with copperhead envenomation had

echinocytosis noted on blood smear evaluation. There are several

steroid administration, although that seems unlikely after one antiinflammatory dose of corticosteroids in hospital.

possible explanations for this difference. First, evaluation of echi-

Antibiotic usage for snake envenomation is controversial

nocyte formation in humans showed that a venom concentration

in both humans and dogs. Studies of microbiology of both

of 200 ng/mL was necessary to cause echinocytosis using various

snakebites and snake oral cavities have shown a mixed population

snake venoms.15 It is possible that lower volumes of venom are

of bacteria, likely reflecting those found in the feces of ingested

delivered from copperheads compared with rattlesnake studies.

prey.22 One study has also shown venom to have antibacterial

Alternatively, phospholipase A2, the phospholipase shown to in-

properties, although only against aerobic isolates.23 Despite

duce echinocytosis, could be present in decreased concentrations in

studies on copperhead bites in humans questioning the necessity

copperhead venom as compared with rattlesnake venom.16

of antibiotic therapy for snake envenomation, studies of dogs

Fourteen percent of dogs were hypercalcemic on presenta-

bitten by snakes document the use of empirical antibiotic ther-

tion; however, none had ionized Ca evaluated. The hypercalcemia

apy.5,19 Both the flora within snakes’ mouths and on dogs’ skin

is likely due in part to hemoconcentration as all dogs also had

may factor into antibiotic choices for clinicians. No dog bitten by

elevated albumin concentrations. In humans, creatine kinase is

a copperhead was re-presented to the study authors’ emergency

used as a marker of envenomation severity and it is hypothesized

facility for snakebite-associated abscess formation. During follow-

that increased Ca may be due to rhabdomyolysis in association

up questioning, one owner reported an infection at the bite site,

14

with local envenomation effects. All dogs with creatinine kinase

but not severe enough to cause re-presentation to another facility

measurements had values within the normal range in this study.

after discharge. There are no known prospective studies in dogs

Ten percent of dogs were mildly hypokalemic on presentation.

evaluating the use of antimicrobials in snakebites or evaluating

None were azotemic and none of the hypokalemic dogs were

snakebite wounds for infection. Antibiotics were administered to

hyponatremic. It has been hypothesized that hypokalemia in snake

the majority of the dogs in this study.

envenomations is a result of cation depletion during red blood 16

Median duration of hospitalization in dogs was 14.8 hr,

cell membrane transformation and formation of echinocytes. In

and dogs presented (on average) 1 hr after envenomation, meaning

this study, the single dog with echinocytes did have a low serum

most dogs were observed at least 16 hr postenvenomation.

potassium concentration. The hypokalemia reported in the re-

However, that time period was almost 10 hr shorter than the

mainder of the dogs may be secondary to a shift of potassium

duration of hospitalization in humans admitted for copperhead

from the extracellular fluid to the intracellular fluid as a conse-

envenomation.10 The difference in hospitalization may be related

17,18

to the time of maximal swelling. In humans, maximal swelling

The most commonly recommended treatments for dogs

is thought to occur 36 hr postenvenomation.19 In the patients

bitten by rattlesnakes include volume expansion, analgesia, anti-

included in this study, in which changes in swelling and inflam-

venin administration, and antibiotic therapy.3,5 No dogs bitten

mation were documented (n ¼ 6), a median time of 6.9 hr from

by copperheads required the use of antivenin. In humans with

presentation to improved swelling was noted. This difference in

copperhead envenomation, clinical management most frequently

time to maximal swelling between dogs and humans may possibly

quence of catecholamine release.

342

JAAHA |

50:5 Sep/Oct 2014

Copperhead Envenomation in 52 Dogs

be due to either skin perfusion differences causing faster accu-

Clinicopathological abnormalities such as thrombocytopenia,

mulation of inflammatory cytokines at the bite site in dogs or

elevated clotting times, and leukocytosis, were mild and re-

because the small number of dogs with swelling timelines recorded

quired no further treatment. Most dogs were treated with

do not accurately reflect the typical course of envenomation.24

antimicrobials, analgesics, and fluid therapy. No dogs bitten by

All dogs survived to discharge. That finding was in contrast to

copperheads in this study required the use of antivenin and all

rattlesnake envenomation, in which mortality rates ranged from 1

survived to discharge. There were rare instances of necrosis at the

3,4

to 19%.

Copperhead venom is significantly less potent than that

of either moccasins or rattlesnakes.1 It is therefore not surprising

bite site. Copperhead envenomation in dogs in this study appears to be self-limiting and responsive to supportive care.

that the course of copperhead envenomation in dogs appears largely self-limiting and minor. One study of Eastern diamondback rattlesnake envenomation found that smaller dogs had a worse prognosis.3 That finding was not reflected in copperhead envenomation in dogs because all dogs survived to discharge with minimal intervention beyond supportive care. Based on the lack of severe clinicopathological, hemodynamic, or local effects observed in the dogs in this study, it is reasonable to conclude that similar to humans, copperhead bites in dogs are largely selflimiting injuries requiring minimal veterinary interventions beyond analgesia and monitoring. The limitations of this study are similar to those inherent in all retrospective studies. Information is limited to that which was recorded in the medical record at the time of hospitalization. Comparing outcomes is difficult without standardized treatment. Additionally, although the study was designed to avoid inclusion of snakes other than copperheads, there is the chance that dogs were bitten by snakes other than copperheads because counties surrounding Wake County contain moccasins and rattlesnakes. Follow-up information was limited. Additionally, it is known that up to 25% of snakebites are “dry,” containing no venom, and bites that do inflict venomation can contain various amounts of venom.25 This varying amount of venom makes it difficult to compare one case to another in terms of severity of signs and outcome. Finally, the patient population was drawn from a number of years, with changing clinicians and treatment recommendations. Future prospective studies evaluating the time to peak clinical signs could help guide hospitalization and treatment decisions. Additionally, the use of antibiotics, not just in copperhead envenomations but other snake envenomations as well, should be evaluated. Prospective studies with additional follow-up could better reveal the extent of local tissue damage after discharge from the hospital and assist in decisions regarding the need for antibiotic therapy.

Conclusion Clinical signs associated with copperhead envenomation in dogs most commonly included swelling, pain, and ecchymosis.

REFERENCES 1. Gold BS, Dart RC, Barish RA. Bites of venomous snakes. N Engl J Med 2002;347(5):347–56. 2. Peterson M. Biotoxins, reptiles. In: Plumlee K, ed. Clinical veterinary toxicology. St. Louis (MO): Mosby Elsevier; 2004:104–11. 3. Willey JR, Schaer M. Eastern Diamondback Rattlesnake (Crotalus adamanteus) envenomation of dogs: 31 cases (1982–2002). J Am Anim Hosp Assoc 2005;41(1):22–33. 4. Hackett TB, Wingfield WE, Mazzaferro EM, et al. Clinical findings associated with prairie rattlesnake bites in dogs: 100 cases (1989– 1998). J Am Vet Med Assoc 2002;220(11):1675–80. 5. McCown JL, Cooke KL, Hanel RM, et al. Effect of antivenin dose on outcome from crotalid envenomation: 218 dogs (1988–2006). J Vet Emerg Crit Care (San Antonio) 2009;19(6):603–10. 6. Russell FE, Carlson RW, Wainschel J, et al. Snake venom poisoning in the United States. Experiences with 550 cases. JAMA 1975;233(4): 341–4. 7. Gold BS, Wingert WA. Snake venom poisoning in the United States: a review of therapeutic practice. South Med J 1994;87(6):579–89. 8. Gilliam LL, Brunker J. North American snake envenomation in the dog and cat. Vet Clin N Am Small Anim Pract 2011;41:1239–59. 9. Bronstein AC, Spyker DA, Cantilena LR Jr, et al. 2009 Annual Report of the American Association of Poison Control Centers’ National Poison Data System (NPDS): 27th Annual Report. Clin Toxicol [Phila] 2010;48(10):979–1178. 10. Thorson A, Lavonas EJ, Rouse AM, et al. Copperhead envenomations in the Carolinas. J Toxicol Clin Toxicol 2003;41(1):29–35. 11. Braswell AL, Palmer WM, Beane JC. Venomous snakes of North Carolina. North Carolina State Museum of Natural Sciences, Raleigh, NC; 2003:32. 12. Barceloux D. Terrestrial snakes. In: Barceloux D, ed. Medical toxicology of natural substances. Los Angeles (CA): Wiley; 2008:1032–46. 13. Swenson S, Bush LR, Markland FS. Chimeric derivative of fibrolase, a fibrinolytic enzyme from southern copperhead venom, possesses inhibitory activity on platelet aggregation. Arch Biochem Biophys 2000;384(2):227–37. 14. Goddard A, Schoeman JP, Leisewitz AL, et al. Clinicopathologic abnormalities associated with snake envenomation in domestic animals. Vet Clin Pathol 2011;40(3):282–92. 15. Flachsenberger W, Leigh CM, Mirtschin PJ. Sphero-echinocytosis of human red blood cells caused by snake, red-back spider, bee and blue-ringed octopus venoms and its inhibition by snake sera. Toxicon 1995;33(6):791–7. 16. Walton RM, Brown DE, Hamar DW, et al. Mechanisms of echinocytosis induced by Crotalus atrox venom. Vet Pathol 1997;34(5): 442–9. 17. Halperin ML, Kamel KS. Potassium. Lancet 1998;352(9122):135–40.

JAAHA.ORG

343

18. Peterson ME. Snake bite: pit vipers. Clin Tech Small Anim Pract 2006;21(4):174–82. 19. Walker JP, Morrison RL. Current management of copperhead snakebite. J Am Coll Surg 2011;212(4):470–4, discussion 474–5. 20. Cunningham ER, Sabback MS, Smith RM, et al. Snakebite: role of corticosteroids as immediate therapy in an animal model. Am Surg 1979;45(12):757–9. 21. Russell FE, Emery JA. Effects of corticosteroids on lethality of Ancistrodon contortrix venom. Am J Med Sci 1961;241:135–9.

344

JAAHA |

50:5 Sep/Oct 2014

22. Abrahamian FM, Goldstein EJC. Microbiology of animal bite wound infections. Clin Microbiol Rev 2011;24(2):231–46. 23. Talan DA, Citron DM, Overturf GD, et al. Antibacterial activity of crotalid venoms against oral snake flora and other clinical bacteria. J Infect Dis 1991;164(1):195–8. 24. Davies B, Morris T. Physiological parameters in laboratory animals and humans. Pharm Res 1993;10(7):1093–5. 25. Parrish HM, Carr CA. Bites by copperheads (Ancistrodon contortrix) in the United States. JAMA 1967;201(12):927–32.