Chapter 175 Ferrets
Clinical Techniques
RESTRAINT
• Most pet ferrets are gentle, tractable, and are easy to restrain without assistance. Often only minimal restraint is needed when performing a physical examination. Some ferrets may be lightly restrained on the examination table. Others will need to be restrained in a firmer manner.
• Tractable ferrets can be lightly restrained on an examination or treatment table by placing one hand under the chest and lifting slightly.
• Energetic ferrets may be restrained by scruffing (Fig. 175-1). Use one hand to grasp the skin over the back of the neck and lift the ferret up, suspending all the limbs. Stroke the abdomen with a downward motion to relax the ferret. The ferret’s back may be supported with the other hand, or the ferret may then be reclined along the forearm of the arm used to scruff the ferret. Most ferrets will become very relaxed, although some young ferrets and some females may resist.
• Firm restraint is often required when administering vaccinations or when performing treatment procedures. Control the head by scruffing, or by cupping the back of the ferret’s neck and placing the thumb and fingers along the caudal border of the mandibles. Place the other hand over the pelvis to restrain the hindquarters on the table top with the hind legs underneath the body; do not pull the legs back.
• Aggressive ferrets, such as nursing females, kits, or ferrets raised with little human contact, are uncommon. Restrain these ferrets by the scruff of the neck, using the techniques previously described. Avoid using leather gloves, which are awkward. Use sedation if necessary.
DIAGNOSTICS
Blood Collection
There are several suitable sites for blood collection in ferrets:
Indications
• Cephalic or lateral saphenous venipuncture may be used to obtain small amounts of blood (<1.0 ml) for a packed cell volume (PCV), blood glucose, complete blood cell count (CBC), or serum biochemistry analysis.
• The jugular vein, cranial vena cava, cephalic vein, or ventral tail artery may be used to collect larger volumes of blood.
Other Considerations
• Sedation: Collection of blood from the jugular veins, cranial vena cava, or ventral tail artery may require sedation and/or the assistance of two people for restraint. Sedation is rarely required for venipuncture of cephalic, lateral saphenous, or jugular veins.
• The normal hematocrit of ferrets is high; draw three times as much blood as the volume of plasma or serum required. (See Tables 175-1 and 175-2 for blood values reported in normal ferrets.)
• The PCV, red blood cell count (RBC), hemoglobin, white blood cell count (WBC), and plasma proteins often rapidly decrease after induction of isoflurane anesthesia.
Table 175-2 REFERENCE RANGES FOR SERUM BIOCHEMISTRY VALUES IN FERRETS
| Value | Albino* | Fitch† |
|---|---|---|
| Total protein (g/dl) | 5.1–7.4 | 5.3–7.2 |
| Albumin (g/dl) | 2.6–3.8 | 3.3–4.1 |
| Glucose (mg/dl) | 94–207 | 62.5–134 |
| Fasting glucose (mg/dl) | 90–125‡ | |
| Blood urea nitrogen (mg/dl) | 10–45 | 12–43 |
| Creatinine (mg/dl) | 0.4–0.9 | 0.2–0.6 |
| Sodium (mmol/L) | 137–162 | 146–160 |
| Potassium (mmol/L) | 4.5–7.7 | 4.3–5.3 |
| Chloride (mmol/L) | 106–125 | 102–121 |
| Calcium (mg/dl) | 8.0–11.8 | 8.6–10.5 |
| Phosphorus (mg/dl) | 4.0–9.1 | 5.6–8.7 |
| Alanine aminotransferase (U/L) | 82–289 | |
| 78–149§ | ||
| Aspartate aminotransferases (U/L) | 28–120 | 57–248§ |
| Alkaline phosphatase (U/L) | 9–84 | 30–120 |
| 31–66§ | ||
| Bilirubin (mg/dl) | <1.0 | 0–0.1§ |
| Cholesterol (mg/dl) | 64–296 | 119–209§ |
| Carbon dioxide (mmol/L) | 16.5–28 | 16–28§ |
* Combined values of male (N = 40) and female (N = 24) ferrets from Thornton PC, Wright PA, Sacra PJ, Goodier TEW: The ferret, Mustela putorius furo, as a new species in toxicology. Lab Anim 13:119–124, 1979.
† Combined values of intact male, female, and castrated male ferrets (total N = 13, aged 4–8 mo) from Lee EJ, Moore WE, Fryer HC, Minocha HC: Haematological and serum chemistry profiles of ferrets (Mustela putorius furo). Lab Anim. 16:133–137, 1982, except where noted.
‡ From Brown S: Personal communication, 1995.
§ Combined values from cardiac and orbital venipuncture of male ferrets (N = 16)
from Fox JG: Normal clinical and biologic parameters. In: Fox JG (ed): Biology and Diseases of the Ferret. Philadelphia: Lea & Febiger, 1988, pp 159–173.
Techniques
Cephalic Vein
• Collect blood from the cephalic vein in ferrets using the same restraint technique described for dogs and cats.
• Use an insulin syringe with a 28-gauge needle or a 1 cc tuberculin syringe with a 25-gauge needle to collect volumes of blood up to 1.0 ml. Larger volumes of blood may be collected with a 3 cc syringe and a 25-gauge needle.
Lateral Saphenous Vein
• The lateral saphenous vein runs diagonally across the lateral surface of the hindleg, just proximal to the hock.
Jugular Vein
• Several methods are described for jugular venipuncture:
• The ferret may be placed in sternal recumbency at the edge of the table. Extend the head dorsally with the front legs held down, out of the path of the venipuncturist.
• Alternatively, wrap the ferret in a towel with the front legs drawn back along the thorax, leaving the head and neck extended from the towel. Position the ferret in dorsal recumbency, and extend the head and neck by scruffing.
Cranial Vena Cava
• This procedure is referred to as cranial vena cava venipuncture, but, in reality, blood is collected from the jugular vein as it passes into the thoracic cavity at the thoracic inlet.
Blood collection from the cranial vena cava requires complete immobilization of the ferret; otherwise, do not attempt the procedure. Use sedation or the help of two assistants for restraint.
• Do not use this site if intrathoracic disease (e.g., mediastinal mass, mega-esophagus) or coagulopathy is suspected.
Technique
1. Place the ferret in dorsal recumbency. One assistant restrains the head and neck in extension while holding the forelegs alongside the thorax. A second assistant restrains the hindquarters without pulling the rear legs back. Precise positioning facilitates the procedure.
2. Palpate the manubrium and locate the “notch” on either side where the manubrium and the first rib meet.
3. Insert a 3-ml syringe with a 25-gauge, 5/8-inch needle at either notch and direct the needle at a shallow angle (<45 degrees) along an imaginary line running from the notch toward the opposite rear leg.
Ventral Tail Artery
Technique
1. Scruff the ferret and place it in dorsal recumbency (wrapping it in a towel may help with restraint), or anesthetize the ferret and place it in dorsal recumbency.
4. Insert the needle on the ventral midline of the tail at 30-degree angle toward the body approximately 2 to 3 cm from the anus.
5. Advance the needle to the bone; withdraw it slowly while applying a slight vacuum to the syringe.
Collection of Blood for Transfusion
A detailed discussion of the techniques used for blood collection for transfusion and blood transfusion is presented in the Hematopoietic System section in this chapter.
Diagnostic Imaging
Radiography
• Use standard radiographic techniques (see Chapter 4), including sedation for correct positioning and to limit exposure of the technician, as well as high detail radiographic film and cassettes.
Bone Marrow Aspiration
• The indications, guidelines, and techniques for bone marrow sampling are the same as those described for dogs and cats. (see Chapter 22)
• Preferred sites include the proximal femur and humerus. The iliac crest may be used for sample collection as well, but can be a difficult site to access.
Splenic Aspiration
Fine-needle aspiration of the spleen has been performed successfully in ferrets and is a rapid means of evaluating splenic cytology. In ferrets, the only contraindication is suspected hemangiosarcoma of the spleen. Sedation is rarely necessary, but is recommended if the ferret persistently struggles.
Technique
1. Two assistants are recommended for restraint. Place the ferret in dorsal recumbency. One assistant should restrain the head and neck by scruffing the ferret with one hand. The other hand is used to restrain the forelimbs. A second assistant restrains the hind limbs by placing one hand around the pelvis.
4. Insert a 25-gauge needle attached to a 3-ml syringe to the hub at a perpendicular angle to the skin and aspirate from the spleen.
THERAPEUTIC TECHNIQUES
Intravenous Therapy
Sedation is often required for placement of a butterfly or indwelling intravenous (IV) catheter, or for small-volume IV therapy.
• For small-volume IV therapy (0.3-0.4 ml), use an insulin syringe. The cephalic or lateral saphenous veins are the preferred sites for injection. Sedation may not always be required for a single injection.
• A 25-gauge butterfly catheter may be used to administer larger, single-dose volumes into the cephalic vein.
• An indwelling catheter can be placed in the cephalic, lateral saphenous, or jugular vein. Sedation is usually required.
• Flush indwelling catheters with small volumes of heparinized saline solution to maintain catheter patency.
• Peripheral indwelling catheters can be placed rapidly and are useful in emergency situations and for surgery.
Cephalic or Saphenous IV Catheter Placement
Technique
2. Tent the skin over the vein and make a small cut-down incision in the skin with a 22-gauge needle, taking care to avoid the vein.
3. Introduce a 1/4–1/2 inch indwelling catheter (20-24 gauge) through the cut-down incision and into the vein.
4. When catheterizing small or debilitated ferrets it is often helpful to attach a tuberculin syringe containing heparinized saline to the catheter hub after removing the stylet. The heparinized saline may then be flushed through the catheter, dilating the vein while the catheter is advanced. The person holding off the vein must release the vein if this technique is used.
Jugular Catheter Placement
Intraosseous Catheter Placement
Technique
2. Wearing a sterile surgical glove, palpate the top of the greater trochanter, and locate the trochanteric fossa.
3. Introduce the tip of a 20- or 22-gauge spinal needle with stylet in place into the trochanteric fossa, and advance the needle parallel to the long axis of the femur through the cortical bone and into the medullary cavity. Flush with heparinized saline.
Subcutaneous and Intramuscular Injections
• IM injections may be given in the quadriceps, the semimembranosus-semitendonosus muscles of the hind limbs, or in the expaxial muscles of the lower back.
Fluid Therapy
• The daily fluid requirement for ferrets has not been reported but can be estimated at 70 to 100 ml/kg/day. Adjust for dehydration and fluid loss.
• IV or IO fluid therapy is used for a wide range of medical and surgical situations, and is recommended for ferrets that are >5% dehydrated.
• IV or IO fluids must be administered with an infusion pump. Fluids may be given as a continuous infusion, may be administered by continuous infusion, or may be given in 2 to 3 bolus doses over a 24-hour period.
Oral Therapy
• If possible, compound medications formulated in tablet or capsule form into liquid suspensions, or crush and mix them with a sweet-tasting substance such as Nutri-Cal (Evsco Pharmaceuticals) feline hairball laxative, or fruit-flavored syrup, and administer by syringe.
Nutritional Support
• Supplemental feeding is important in the management of anorectic or critically ill ferrets, and in the treatment and prevention of hypoglycemic episodes associated with insulinoma.
• Most ferrets can be force-fed dietary supplements by syringe. Once they acquire a taste for a given supplement, it may be possible to offer it in a bowl.
Drug-Dosing Guidelines
• Use of all medications is considered off-label for the ferret; there are no approved drugs available for ferrets in the United States.
• Several exotic animal formularies are commercially available that include drug dosage information on ferrets.
• Many ferrets become lethargic when placed on enalapril (Enacard, Merck Agvet) for cardiac disease. Start with a very low dose (0.25-0.5 mg/kg) q48h PO. Some ferrets cannot tolerate more than every-other-day therapy.
• Ivermectin (0.06 mg/kg) q30d PO for heartworm prevention; (0.05 mg/kg) once 3 to 4 weeks after adulticide treatment as a heartworm microfilaricide; (0.50-1.0 mg/kg) PO, SC, repeat in 14 days for sarcoptic mites; (1 mg/kg) instill half the calculated dose into each ear and repeat in 14 days for ear mites.
Blood Transfusions
A detailed discussion of the techniques used for blood collection for transfusion and blood transfusionis presented in the Hematopoietic System section in this chapter.
Urinary Catheterization
• Sedation or isoflurane anesthesia facilitates urinary catheterization. The procedure may be difficult in ferrets with urethral disease or urethral calculi.
Males
2. Identify the urethral opening, which lies ventral to the tip of the penis. It is helpful to place a 24-gauge IV catheter (with stylet removed) into the urethral opening as a guide.
3. Use a ferret urinary catheter (Slippery Sam ferret urinary catheter, Cook Veterinary Products) an open-ended tomcat catheter, or a #3.5-Fr. feeding catheter. A wire stylet may be useful.
Females
1. Position in ventral recumbency with the hindquarters elevated and use a tomcat catheter or a 3.5-Fr. feeding tube with or without a stylet.
Sedation
Isoflurane administered by face mask is the most convenient method to immobilize a ferret for procedures such as venipuncture and radiography. Induction and recovery are rapid.
Doses for parenteral agents used in ferrets are listed in Table 175-3.
Table 175-3 DRUGS RECOMMENDED FOR CHEMICAL RESTRAINT AND ANALGESIA OF FERRETS
| Drug | Dosage (mg/kg) | Route |
|---|---|---|
| Chemical Restraint | ||
| Acepromazine | 0.1–0.3 | IM, SC |
| Ketamine plus acepromazine* | 25–35 | IM, SC |
| 0.2–0.3 | ||
| Ketamine plus diazepam | 25–35 | IM |
| 2–3 | ||
| Ketamine plus xylazine | 10–25 | IM |
| 1–2 | ||
| Analgesics | ||
| Buprenorphene | 0.01–0.03 mg/kg q8–12h | SC, IM, IV |
| Butorphanol tartrate | 0.05–0.5 mg/kg q8–12h | SC, IM |
| Carprofen | 1 mg/kg q12–24h | PO |
| Flunixin meglumine | 0.5–2.0 mg/kg q12–24h | IM, IV |
* Use this combination for minor surgery. IM, intramuscular; SC, subcutaneous.
• Butorphanol tartrate has been used at SC, IM, IV, but can cause very profound sedation in some ferrets.
• Ketamine alone does not produce effective muscle relaxation. Use in combination with acepromazine for minor surgical procedures, or with diazepam for more complicated procedures.
• Medetomidine is not analgesic; animals will respond to painful stimuli. Use with an analgesic agent. This agent is reversible (atapamazol).
• Tiletamine-zolazepam (Telazol, Fort Dodge) gives variable muscle relaxation but is useful for immobilization for procedures such as venipuncture, radiography, and electrocardiography. Recovery may be prolonged.
Anesthesia and Analgesia
• Premedicate with parenteral agents followed by face-mask induction. Alternatively ferrets may be given inhalant agents without premedication via chamber or face-mask induction.
• Isoflurane is the inhalant anesthetic most commonly used in small mammal practice. Sevoflurane is used in some practices as well. Pharmacokinetic and pharmacologic isoflurane and sevoflurane are very similar; sevoflurane smells better and is better tolerated during face-mask induction.
• Isoflurane does not provide analgesia. Administer an analgesic pre- or intra-anesthesia if a painful procedure is to be performed. Analgesic agents commonly used in ferrets include Buprenorphene (0.01-0.03 mg/kg q8-12h SC, IM, IV), Butorphanol (0.05-0.5 mg/kg q8-12h SC, IM), Carprofen (1 mg/kg q12-24 PO), and Flunixin meglumine (0.5-2.0 mg/kg q12-24h IM, IV).
• Intubate ferrets to facilitate intermittent positive pressure ventilation (IPPV). A 2.5 to 3.5 mm endotracheal tube usually is suitable.
• Follow basic principles of anesthesia for small animals, (see Chapter 2) and provide supplemental heat during surgery; administer IV fluids (isotonic electrolyte solutions supplemented with 2.5-5% dextrose) during long procedures and for insulinoma surgery.
Infectious Diseases of the Ferret
VIRAL DISEASES
Canine distemper and influenza are the two most common viral diseases of the ferret. Influenza is zoonotic between humans and ferrets, and is typically passed from humans to ferrets. Canine distemper is 100% fatal in the ferret, making distemper vaccination imperative.
Canine Distemper
Etiology
• The canine distemper virus (CDV) is a paramyxovirus. Transmission occurs through direct contact with infected animals of any species, and through contact with fomites such as in shoes or clothing.
Clinical Signs
• Pyrexia (>40°C), anorexia, and profuse mucopurulent naso-ocular discharge develop as the disease progresses.
Ferrets develop a distinct pattern of hyperkeratosis of the integument of the chin, lips, and footpads. Lesions may occur in the rectal and inguinal areas as well.
Diagnosis
Preliminary diagnosis of CDV may be based primarily on the history, physical examination, and clinical signs, which are unlike those of any other disease in the ferret.
• The history often reveals that the animal is unvaccinated, overdue for booster vaccination, or is improperly vaccinated. There is often no evidence of direct exposure to an infected animal because fomite transmission can occur.
• Differential diagnoses early in the disease include influenza and bacterial conjunctivitis. As the disease progresses, development of the integumentary lesions around the chin, lips, and footpads are pathognomonic.
• A fluorescent antibody test can be performed on blood smears, conjunctival scrapings, or mucous membrane scrapings. This test is only useful in the first days of disease onset; false-negative results are common. Modified live vaccine strains of canine distemper will not affect this test.
• Plasma samples can be submitted to measure antibody titer. A positive result is not always diagnostic of disease because both infected and vaccinated ferrets can have a positive titer. Unvaccinated ferrets with a positive titer are likely infected with CDV.
• Fluorescent antibody staining may be performed on imprints of the lymph nodes, bladder epithelium, and cerebellum postmortem.
Treatment
Treatment for canine distemper is rarely effective, and is limited to supportive care only. Most affected animals must be euthanized.
• Disinfect the household thoroughly using 0.2% Roccal (Upjohn), 0.75% phenol, or 2% to 5% sodium hydroxide.
Prevention
• Vaccinate all ferrets in the household or facility. Currently only two vaccines are approved for use in ferrets: PureVax (Merial, Athens, GA), and Fervac-D (United Vaccines, Inc., Madison, WI). Give 1 ml SC, using the following schedule:
• If the dam is vaccinated: Vaccinate kits at 8 weeks of age and repeat vaccination every 3 to 4 weeks until the kits are 16 weeks of age.
• If the dam is unvaccinated: Vaccinate the kits at 6 weeks of age and repeat every 3 to 4 weeks until the kits are 16 weeks of age.
• Revaccinate annually. Sources claim that immunity lasts for 3 years; however, outbreaks have been known to occur 18 months after vaccination.
• Use of serum titers as a method to evaluate an animal’s current immunological status is unsubstantiated.
• Quarantine new ferrets and canines for 4 weeks before exposure to other resident animals. Vaccinate new animals immediately after acquisition at the beginning of the quarantine period.
• Use of Galaxy D (Schering-Plough Animal Health Co., Omaha, NE) for distemper vaccination has been described. Use of this product in ferrets is extra-label. This product has proved effective in preventing canine distemper in young ferrets; however, duration of immunity is unknown.
Influenza
Etiology
The influenza virus is an orthomyxovirus. Ferrets are susceptible to influenza A and B; this is the only documented zoonotic disease of the ferret. Human-to-ferret transmission is more common than ferret-to-human transmission. Transmission occurs by direct contact with naso-ocular discharges, and via inhalation of aerosolized droplets.
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