Cerebral cysticercosis in a woodchuck (Marmota monax)

A juvenile woodchuck (Marmota monax) with vestibular signs was found in Woodbridge, Ontario (Canada) and later euthanized. At necropsy there was marked distortion of the right side of the skull, where a large, fluctuant, subcutaneous mass extended under the zygomatic arch and caudally from the right eye towards the right ear. The mass was multiloculated and contained a large number of tapeworm cysticerci, each about 1 to 2 mm in diameter. The third and lateral ventricles of the brain were dilated and contained large numbers of similar cysticerci. Based on the exogenous budding of cysts and the morphology of the scolex in each cyst, they were identified as cysticerci of Taenia crassiceps. This is the first report of cerebral cysticercosis in a woodchuck.     

Lymphosarcoma in the laboratory woodchuck (Marmota monax)

From 1979 to 1999,28 cases of lymphosarcoma were identified in the Cornell University woodchuck colony (prevalence rate: 152/100,000/yr). The prevalence of lymphosarcoma was similar in woodchucks not infected with the woodchuck hepatitis virus (WHV) and in chronic carriers of WHV. Males (13) and females (15) alike were affected (mean +/- SD age 4.7 +/- 2.92 years; range, 0.5 to 9 years). On the basis of the major organ system involved, woodchuck lymphosarcoma was classified as multicentric (12 cases, 43%), alimentary (5 cases, 18%), cranial mediastinal (5 cases, 18%), and miscellaneous (6 cases, 21%). A cutaneous form was not observed. Morphologic criteria similar to those of the Kiel classification were used for light microscopic classification. All Kiel categories-except the immunoblastic form-were found: 17 cases (61%) were centroblastic, and 6 were lymphocytic (21%). Other categories (centrocytic and plasmacytoid) were recognized less frequently. Immunophenotyping of 27 cases revealed 15 (56%) B cell (CD3-/CD79a+ or CD3-/BLA.36+), 7 (26%) T cell (CD3+/CD79a-/BLA.36-), and 5 (18%) non-T non-B cell (CD3-CD79a-/BLA.36-) lymphosarcomas. Lymphosarcoma in woodchucks develops at a higher rate than that observed in humans or companion animals, and WHV infection has no effect on prevalence. The anatomic and Kiel classification used in domestic species also can be used in woodchucks. Commercially available alpha-CD3, alpha-CD79a, and alpha-BLA.36 antibodies were useful for immunophenotyping woodchuck lymphosarcomas.     

Parasites of the laboratory woodchuck (Marmota monax)

The parasite burden of captive and colony-born woodchucks maintained in laboratory animal facilities was determined and compared to woodchucks recently trapped. Microfilariae of Ackertia marmotae in blood or dermis were most commonly observed in trapped woodchucks. There was a linear decrease in woodchucks positive for microfilariae after introduction in the laboratory colony, but even after 39 months, 53% were positive. Microfilaremia or microfilariderma were never observed in colony born woodchucks. Eggs or oocysts of Obeliscoides cuniculi, Citellina triradiata and Eimeria sp. were found by fecal flotation. The O. cuniculi population declined exponentially in captive woodchucks following colony entry, and this nematode was never found in colony-born woodchucks. However, low rates of infection with Citellina and Eimeria sp. were found in the colony-born group. Ixodes cookei, Oropsylla sp., and Androlaelaps sp. ectoparasites were observed commonly in recently trapped woodchucks, but were not present in any woodchucks maintained in the colony. Clinical disease associated with parasitic infection was not observed.     

Seasonal ultrastructural variations in pinealocytes of the woodchuck,Marmota monax

The ultrastructure of the pinealocyte in the woodchuck, Marmota monax, was studied during the four seasons of the year. Fall cells have a fairly uniform cytoplasmic density, organelles consistent with synthetic and/or secretory activity and rather extensive pericapillary and intercellular spaces. Many winter pinealocytes are nearly devoid of ribosomes and granular endoplasmic reticulum but contain lipid droplets associated with mitochondria. Pericapillary and intercellular spaces are minimal. Spring glands have the greatest variation in cytoplasmic density with intercellular and pericapillary spaces similar to that seen in fall glands. Cells containing electron dense cytoplasm have Golgi zone associated, secretory granules, free ribosomes, short sections of granular endoplasmic reticulum and dense bodies. Cells with a more electron lucent cytoplasm are similar to the most frequently observed summer pinealocytes which have numerous Golgi zones but few associated secretory granules. Microtubules are prominent in the cytoplasm of these cells, the plasma membranes are smooth and intercellular and pericapillary spaces are minimal. A yearly rhythm or cyclic activity of the pinealocyte is suggested.     

Erthyrocyte changes in the hibernating woodchuck (Marmota monax)

Active woodchucks were maintained at 23 °C with a photoperiod of LD 12:12. Hibernating woodchucks were kept at 10 °C with a photoperiod of LD 8:16. Blood was collected and the erythrocytes were counted and measured.The data showed an increase in red blood cell count, a decrease in erythrocyte diameter and a decrease in mean corpuscular diameter during hibernation. The hematocrit was the same in both the hibernating and active woodchucks. It would appear that there are a greater number of smaller cells present in the circulation of the hibernating woodchuck as compared to that of the active woodchuck. This may result from the combined effects of increased life span, decreased destruction and continued, but slowed, production of red blood cells.     

Laboratory assessment of hepatic injury in the woodchuck (Marmota monax)

Normal reference values for total serum protein, albumin, cholesterol, alanine aminotransferase (ALT), aspartate aminotransferase (AST), sorbitol dehydrogenase (SDH), gamma glutamyl transferase (GGT), alkaline phosphatase (AP), and total bilirubin were established in 48 clinically healthy woodchucks. To validate the use of these biochemical tests in the woodchuck for assessment of liver injury, carbon tetrachloride was administered to produce hepatocellular necrosis and the common bile duct was surgically occluded to produce cholestasis. Biochemical tests were performed prior to experimental treatment and thereafter in surviving woodchucks for a period of 6 weeks. There were marked increases in the serum activities of AST, ALT, and SDH following carbon tetrachloride administration and all 3 enzymes appeared to be useful markers of acute hepatocellular injury. The predominate biochemical abnormalities in woodchucks with bile duct obstruction were hyperbilirubinemia, hypercholesterolemia and increased serum AP and GGT activities. The increase of GGT occurred earlier following bile duct obstruction and the magnitude of increase was greater than that of AP, suggesting that GGT would be the preferred serum enzyme test in the woodchuck for assessment of cholestatic liver injury.     

Congestive cardiomyopathy in the woodchuck, Marmota monax

Congestive cardiomyopathy was diagnosed during post mortem examination in eight of 149 adult woodchucks from New York. The eight woodchucks, four males and four females, died spontaneously without clinical signs of heart failure having been detected. The primary lesion was a grossly enlarged and dilated heart. Histologic lesions consisted of multifocal myocardial degeneration and necrosis. Secondary lesions of congestive heart failure were observed.     

The woodchuck, Marmota monax, as a laboratory animal

The woodchuck or groundhog (Marmota monax) has been used as a biomedical model for studies of obesity and energy balance, endocrine and metabolic function, central nervous system control mechanisms and cardiovascular, cerebrovascular and neoplastic disease. Methods of care of a woodchuck colony, techniques for handling, restraint, anesthesia, blood sampling and breeding were developed.     

Hepatic lesions in woodchucks (Marmota monax) seronegative for woodchuck hepatitis virus

Livers from 128 captive woodchucks (Marmota monax) that were negative for serological markers of woodchuck hepatitis virus (WHV) were examined grossly and histologically. Livers from 19 additional seronegative woodchucks were examined only grossly. The most common finding (61% of histological specimens) was mononuclear cells in portal areas. Moderate to severe portal infiltrates in association with similar scattered mononuclear cell aggregates and extramedullary hematopoiesis, were present in woodchucks that had extrahepatic inflammatory lesions. We concluded that these changes represent a response to a variety of chronic infections and are not specific for WHV infection. Other findings included parasitic granulomas, focal and diffuse lipidosis, bile duct proliferation, lesions secondary to cardiovascular compromise, and vasculitis. Two woodchucks had neoplastic lesions.     

An infrared thermographic study of surface temperature in the euthermic woodchuck (Marmota monax).

Surface temperatures were measured in euthermic woodchucks (Marmota monax) using infrared thermography across a range of ambient temperatures from -10 degrees C to 32 degrees C. The woodchuck keeps surface temperature of the peripalpebral region uniformly high, while head and body surfaces change proportionally with ambient temperature. When ambient temperature was below 0 degrees C, all surface temperatures increased which prevents freezing. At no point did the animals appear to be unable to regulate heat exchange. This species appears to be especially well adapted to the higher temperatures it encounters in its range. Vasomotion in the feet and to a lesser extent in the pinnae was used to regulate heat loss. At ambient temperature of 32 degrees C, mean temperatures of nose surfaces were 0.2 degrees C and 0.3 degrees C less than ambient temperature suggesting a type of counter current cooling mechanism may be present.     

Stimulation of testicular function during the nonbreeding season in the woodchuck (Marmota monax)

Treatment of male woodchucks with a series of s.c. injections of pregnant mare serum gonadotropin (PMSG) and human chorionic gonadotropin (hCG) induced testicular growth, sperm production and marked increase in serum testosterone levels in the fall, approximately 4 mo before the expected spontaneous onset of testicular activity. These results suggest that it may be possible to induce and/or maintain reproductive competence in this species outside of its normally brief breeding season.     

Incisal biting in the mountain beaver (Aplodontia rufa) and woodchuck (Marmota monax)

Analysis of synchronously recorded cine-radiographs and electromyograms in two rodents (Aplodontia rufa and Marmota monax) demonstrates that jaw movements and muscle activiteis during incisal functions are distinctly different from those found during mastication. Movements during incisal biting are primarily along the midline, accompanied by symmetrical activity of the jaw adductor muscles. Most biting cycles do not end in contact between upper and lower incisors. When contact does occur, the lower incisors are dragged along the lingual surfaces of the upper incisors. Cropping, or tip-to-tip occlusion of upper and lower incisors, was not observed. Sharpening of the lower incisors, a behavior which may be unique to the Rodentia, was recorded in both A. rufa and M. monax. During sharpening, the lingual surface of the lower incisor is dragged across the tip of the upper incisor producing a lingual wear facet. Like incisal biting, sharpening movements are primarily confined to the midline, although there may be lateral movements in some sharpening cycles. Sharpening cycles are among the most rapid cyclic movements recorded in mammals, as the mean frequencies of sharpening are 11 cycles/s in A. rufa and 8 cycles/s in M. monax. © 1995 Wiley-Liss, Inc.