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Anemia in ferrets: Clinical case challenges (Proceedings)

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Aug 01, 2009

Ferrets are very similar to more 'traditional' companions in many ways. They also develop many similar disease processes. For all ferrets with anemia, the author recommends that the diagnostic workup begins in a similar fashion to the dog and the cat. CBC, platelet count, biochemistry panel, urinalysis, sometimes thoracic radiographs, and abdominal ultrasound all may be part of the minimum data base. From there, the diagnostic pathway may vary slightly but should still follow a logical sequence as it would in a dog or a cat. This lecture will use a series of case correlates to illustrate the more common diseases of ferrets.

Diagnostic Evaluation

Normal PCV in a ferret is higher than most dogs and cats, varying from 45-65% (varying depending on laboratory). The spleen remains a significant contributor to red cell production throughout life, and has the ability to greatly enlarge in response to anemia. It is important to realize that the spleen also enlarges for many reasons, including anesthesia, as well as secondary to many systemic illnesses. The spleen is normally palpable, and when enlarged can occupy much of the abdomen. Hematocrits in ferrets can drop significantly when anesthetized, therefore should be interpreted in light of anesthesia.

As in other patients, anemia can be the result of 3 potential etiologies: blood loss, lack of production, or destruction. It is important to assess for underlying causes for each of these etiologies.

Blood for a PCV can be collected from a peripheral vein using an insulin syringe. Shave the limb if you do not collect blood from ferrets commonly, and try to preserve at least one limb in case a blood transfusion is required. Jugular veins can also be accessed. Although the cranial vena cava is a site that is commonly described for blood collection, this site should be avoided in any anemic ferret due to the potential of coagulopathy.

Bone marrow can be collected from the trochanteric fossa of the proximal femur or the greater tubercle of the proximal humerus. Standard 18-ga bone marrow needles can be used in ferrets. If bone marrow needles are not available, spinal needles or even standard 18-ga needles can be used. When using a standard needle, a bone plug may become lodged within the core of the needle. If this occurs, remove the needle, and replace with a new needle of the same size into the same site. The initial site of entry is usually easily located. If the need for blood transfusion is anticipated, the needle can be flushed and left in the bone and used as an intraosseous catheter.

Core bone biopsies can also be obtained. Use a standard bone marrow needle with the stylet removed. Introduce the needle through the skin, then advance through both cortices of bone, then through the skin on the opposite side of the leg. Leaving the needle in place, insert the stylet to remove the plug of bone through the tip of the needle for sampling.

Splenic aspirates can easily be performed in most ferrets and in some cases can be performed without sedation. Ultrasound is recommended first to evaluate for nodules or focal areas of disease, and if there are focal areas, then ultrasound should be used to guide the aspirate to these areas for sampling. If the spleen appears uniformly affected, ultrasound may not be required. Using a 25-ga needle and 3cc syringe, immobilize the ferret by scruffing and letting the hindlimbs dangle. Immobilize the spleen with one hand, and use the other hand to obtain the aspirate.

Evaluate platelets in the anemic ferret, in addition to a complete blood count (CBC). Although standard clotting times in ferrets have not been established, it may be possible to assess PT and PTT on patientside analyzers. If another ferret is available that can be used for comparison of results. Reticulocyte counts can be performed to assess for regeneration.

Blood transfusions can be administered in ferrets. There is only one known blood type in ferrets, so blood typing is not required, although a major and minor cross match can be performed. Donor ferrets should be anesthetized for blood collection. When available, CPDA or (ACD) are predrawn into the collection syringe, 1-2 ml of anticoagulant per 10 ml blood. If this is not available, heparin can be used. Collect 10ml per kg body weight from the donor ferret. Use a Hemo-nate or similar blood filter and administer the blood by hand over 20-40 minutes while monitoring for transfusion reactions as in other species. If intravenous access cannot be obtained, the transfusion can be administered via an intraosseous catheter.

Obtain a thorough history to determine whether rodenticide or other toxin ingestion may be a factor. Evaluate all body cavities for a source of blood loss. Assess skin and mucous membranes for petechiae or ecchymoses. Evaluate feces and urine for the presence of blood. Since ferrets are carnivores, fecal occult blood tests are inaccurate if ferrets are eating meat-based diet. If it is necessary to perform a fecal occult blood test, there is a product that can be fed for 2-3 days that is soy based (Lafeber Emeraid Carnivore Elemental Diet).

Etiologies

Sources of blood loss in ferrets are similar to other species. Trauma, rodenticide toxicity, gastrointestinal bleeding all should be considered. Although some practitioners have attributed severe anemia to helicobacter enteritis, the author has not seen this in a clinical setting.

The most common causes for lack of production are lymphoma or estrogen-induced bone marrow suppression. Ferrets are induced ovulators, and intact females that are not breeding and are not stimulated to ovulate will suffer from this condition. These females will also have a swollen vulva. However, most ferrets are spayed before they even reach the pet store, so this condition is uncommon. More likely is bone marrow suppression secondary to hyperadrenocorticism. This condition in ferrets is not Cushing's disease as circulating cortisol levels do not elevate. Instead, different combinations of androgenic hormones elevate, and in rare cases, estrogen toxicity can occur. This occurs in males as well as females, and may be independent of alopecia or other signs of adrenal disease. Ecchymoses are visible on skin, bone marrow is suppressed, and prognosis is grave. Blood transfusions before and during surgery are crucial, and it may take weeks for the marrow to recover. Multiple transfusions may be required during the recovery if the patient survives the initial surgery.

Destructive processes are more difficult to recognize in ferrets, as they seem to lack overt signs of destruction. In cases the author has seen, there is no hemolysis, no schistocytes or spherocytes, no autoagglutination. Tick-borne diseases associated with destruction are also not reported in ferrets. If clinical signs and bone marrow sampling do not support loss or lack of production, than the clinician must consider a destructive or immune mediated process and should treat accordingly. Immunosuppressive drugs that can be administered include prednisone or prednisolone, cyclophosphamide, azathioprine, or other drugs used in dogs and cats; combination therapy may be required along with multiple transfusions.

Summary

Anemia in ferrets presents a diagnostic and therapeutic challenge. Clinical evaluation should proceed as it would in a dog or cat. Determine whether there is loss, lack of production, or destruction using standard testing such as ultrasound, splenic aspirates, and bone marrow sampling. Treat according to diagnosis whenever one can be established.