Wild Cottontail Rabbits Research Articles

Causes of morbidity and mortality in wild cottontail rabbits in the eastern United States, 2013-2022.

Interest in causes of mortality of free-ranging, native North American lagomorphs has grown with the emergence of rabbit hemorrhagic disease virus 2 (RHDV2). Over the years 2013-2022, the Southeastern Cooperative Wildlife Disease Study received 119 Sylvilagus spp. case submissions from the central and eastern United States, comprising 147 rabbits. Most (86%) of these submissions occurred after detecting RHDV2 in the United States in 2020. Laboratory data from these rabbits were retrospectively evaluated for major causes, contributors to mortality, and pathogen detections. Gross and histologic examination was performed for 112 rabbits. Common primary causes of death included trauma (n = 49), bacterial disease (n = 31), emaciation (n = 6), and parasitism (n = 6). Among the 32 rabbits with bacterial disease, 12 were diagnosed with tularemia and 7 with pasteurellosis. Rabbits with pasteurellosis had disseminated abscessation, septicemia, and/or polyserositis. Less commonly, cutaneous fibroma (n = 2), notoedric mange (n = 2), encephalitozoonosis (n = 2), neoplasia (round-cell sarcoma; n = 1), and congenital abnormalities (n = 1) were diagnosed. RHDV2 was not detected in 123 rabbits tested. Although RHDV2 has not been detected in wild lagomorphs in the eastern United States, detections in domestic rabbits from the region emphasize the need for continued surveillance. Furthermore, continued surveillance for Francisella tularensis informs public health risk. Overall, increased knowledge of Sylvilagus spp. health furthers our understanding of diseases affecting these important prey and game species.

Only the Good Die Old? Ontogenetic Determinants of Locomotor Performance in Eastern Cottontail Rabbits (Sylvilagus floridanus).

SynopsisFor many animals, the juvenile stage of life can be particularly perilous. Once independent, immature animals must often complete the same basic survival functions as adults despite smaller body size and other growth-related limits on performance. Because, by definition, juveniles have yet to reproduce, we should expect strong selection for mechanisms to offset these ontogenetic limitations, allowing individuals to reach reproductive adulthood and maintain Darwinian fitness. We use an integrated ontogenetic dataset on morphology, locomotor performance, and longevity in wild cottontail rabbits (Sylvilagus floridanus, Allen 1848) to test the hypothesis that prey animals are under selective pressure to maximize juvenile performance. We predicted that (1) juveniles would accelerate more quickly than adults, allowing them to reach adult-like escape speeds, and (2) juveniles with greater levels of performance should survive for longer durations in the wild, thus increasing their reproductive potential. Using high-speed video and force platform measurements, we quantified burst acceleration, escape speed, and mechanical power production in 38 wild-caught S. floridanus (26 juveniles, 12 adults; all rabbits >1 kg in body mass were designated to be adults, based on published growth curves and evidence of epiphyseal fusion). A subsample of 22 rabbits (15 juveniles, 7 adults) was fitted with radio-telemetry collars for documenting survivorship in the wild. We found that acceleration and escape speed peaked in the late juvenile period in S. floridanus, at an age range that coincides with a period of pronounced demographic attrition in wild populations. Differences in mass-specific mechanical power production explained ∼75% of the variation in acceleration across the dataset, indicating that juvenile rabbits outpace adults by producing more power per unit body mass. We found a positive, though non-significant, association between peak escape speed and survivorship duration in the wild, suggesting a complex relationship between locomotor performance and fitness in growing S. floridanus.

Clostridial Enterotoxemia and Coccidiosis in Weanling Cottontail Rabbits ( Sylvilagus audubonii, Sylvilagus floridanus, Sylvilagus nuttallii) from Colorado, USA.

Wild cottontail rabbits ( Sylvilagus spp.), especially young individuals, are one of the most frequent wildlife species presented for rehabilitation at wildlife rehabilitation centers. These species are challenging to rehabilitate, with gastrointestinal (GI) disease being a major cause of morbidity and mortality during the weaning stage. Two organisms, Clostridium spiroforme and Eimeria spp., are frequently associated with GI disease in young domestic rabbits ( Oryctolagus cuniculus) and can result in high rates of morbidity and mortality in this species. Here we present evidence that these two pathogens also play an important role in GI disease in young cottontail rabbits ( Sylvilagus audubonii, Sylvilagus floridanus, Sylvilagus nuttallii) undergoing rehabilitation.

Sodium Provision and Wild Cottontail Rabbits: Morphological Change in Adrenal Glands

A direct relationship exists between sodium (Na) nutrition and morphology of the mammalian adrenal cortex, but little research on the relationship between soil Na levels and herbivore populations exists. Consequently, we assessed the effect of Na on wild cottontail rabbits (Sylvilagus floridanus) inhabiting Na poor soils in southcentral Indiana by characterizing their adrenal mass and histology prior to, and following, provision of supplemental Na. Data and tissues were collected at annual (1985-87) hunter check stations and during the 1987 breeding season at the Atterbury Fish and Wildlife Area

Shope papillomavirus transcription in benign and malignant rabbit tumors

Shope papillomavirus induced benign and malignant tumors from both wild and domestic rabbits were analyzed by the Northern blotting technique for the presence of viral-specific RNAs. Virus-producing benign tumors of wild cottontail rabbits are shown to contain two major RNA species approximately 5000 and 3000 bases in length that originate in the early region and include the majority of the L1 and L2 late open reading frames. Non-productive tumors including wild-rabbit carcinomas, and benign warts and primary and metastatic carcinomas of domestic rabbits uniformly are shown to contain two major viral-specific RNA species, 2400 and 1400 bases in length. These transcripts map entirely within the early region of the viral genome. In addition, Southern blot analysis of metastatic tumors indicates that the viral DNA remains exclusively extrachromosomal and apparently unrearranged supporting previous findings with epithelial malignancies.

Occurrence of Escherichia coli in Wild Cottontail Rabbits

Occurrence of <i>Escherichia coli</i> in Wild Cottontail Rabbits

Occurrence of Escherichia coli in Wild Cottontail Rabbits

Free-ranging cottontail rabbits (Sylvilagus floridanus) from two areas in central Pennsylvania were sampled over a 4-year period. Large numbers of coliforms were isolated from the intestinal tracts of these animals; in 136 of the 141 rabbits sampled, Escherichia coli was found to be a major component of the alimentary flora. Four serogroups (O7, O77, O73, and O103) were predominant among the isolates and were considered resistant coliflora of this species of cottontail rabbit.

EPIDEMIOLOGY OF Herpesvirus sylvilagus INFECTION IN COTTONTAIL RABBITS

The epidemiology of Herpesvirus sylvilagus infection in wild cottontail rabbits was studied in a defined, natural cottontail population over a period of 13 months. Spread of this virus showed significant correlation with seasonal variation as well as with the sex and age of the host. The highest rate of infection occurred during the winter and spring seasons with males over the age of 4 months sustaining a significantly greater percentage of infections than younger males or females of all age groups.

Herpesvirus sylvilagus IN COTTONTAIL RABBITS: ANTIBODY PREVALENCE AND FLEA BURDEN RELATIONSHIPS

A serologic survey of a wild cottontail rabbit (Sylvilagus floridanus) population in southern Wisconsin was conducted from November-March, 1971-72 and November-April, 1972-73, to determine prevalence of antibody against Herpesvirus sylvilagus. Flea burdens on each live-trapped cottontail were quantified by species. All but six of the 5029 fleas collected were Cediopsylla simplex. No correlation was found between flea infestation and viral antibody. Of 101 cottontail rabbits trapped, only six had specific antibody as determined by plaque neutralization in rabbit kidney cell culture. Three of the six developed antibody between January and March of the trapping season. Blood samples from 46 captured rabbits were negative for virus.

New Member of the Herpesvirus Group Isolated from Wild Cottontail Rabbits

A viral agent has been isolated from naturally infected wild cottontail rabbits (Sylvilagus floridanus). The virus appears to have the general physical, chemical, and biological properties of the herpesvirus group. It differs significantly in host range and antigenic structure from the previously recognized herpesviruses and is proposed as a new member of this group of viruses. The name of Herpesvirus sylvilagus is suggested for the agent.

Spontaneous Papillomatosis in Domestic Rabbits

Infectious papillomatosis is an enzootic virus disease of wild cottontail (Sylvilagus) rabbits. What is believed to be the first naturally occuring infection of domestic rabbits is reported, and enzootic infection of the California cottontail rabbit with this virus is suggested. Rabbit papillomatosis is an enzootic disease of cottontail rabbits (Shope, 1933). Geographically, the disease is found in the wild rabbits of Kansas, Iowa, Oklahoma, and Texas. The domestic rabbit and the jack rabbit (Lepus californieus) are also susceptible to this disease (Beard and Rous, 1935). While the virus can be obtained easily from the growths on cottontail rabbits, it is usually not recoverable from papillomas on domestic rabbits. Domestic rabbits are easily infected with the wild cottontail rabbit virus (WRV), but successive passages are usually not successful (Selbie and Robinson, 1947; Shope, 1935). The purpose of this report is to describe cases of naturally-occurring papillomatosis in domestic rabbits raised in Sout...

Fractionation of Shope papilloma virus in cesium chloride density gradients

Virus particles prepared from extracts of glycerinated Shope papilloma tissue of wild cottontail rabbits by means of three alternate low and high speed sedimentations were not uniform in the electron microscope. Variations in size and electron density were seen in negative-contrast preparations. When such particles were centrifuged to equilibrium in a cesium chloride density gradient they separated into four layers corresponding to densities of about 1.29, 1.32, 1.33, and 1.34. Ultraviolet absorption studies, infectivity tests, and the homogeneity of the particles were consistent with the thesis that the most dense particles contained the highest proportion of deoxyribonucleic acid (DNA) and were probably the complete virus. The intermediate layers appeared to have less DNA, and the top layer little or none. In electron micrographs the most dense particles were uniform. Their surfaces were composed of an estimated 60 to 70 capsomeres. The particles in the intermediate layers showed various degrees of emptiness at their centers. The lightest particles appeared to be loose aggregates of capsomeres. When the particles were exposed to fresh cesium chloride, they appeared to become more fragile, many of them disintegrating into free capsomeres on the electron microscope grid. These subunits of the protein coat had a structure suggestive of hollow cylinders or cups. Subunits of the viral core could not be definitely characterized in density gradients or visualized by means of the electron microscope.

Antiviral and Antitumor Immunologic Mechanisms Operative in the Shope Papilloma-Carcinoma System

In 1933 Shope described an infectious papilloma of wild cottontail rabbits. The tumor was regularly transmissible to domestic rabbits on primary inoculation but was not transmissible in indefinite series. He noted that the tumors of 2 animals regressed, whereas in most cases the papillomas persisted indefinitely. During the following 10 years, Rous, Kidd and Beard published extensive studies of these papillomas and of squamous cell carcinomas originating in them. Shope (1937) was the first to note that, although papillomas of domestic rabbits were commonly free of virus as judged by transmission experiments, they nevertheless contained viral antigen as judged by their capacity to stimulate the development of neutralizing antibody and resistance to reinfection following intraperitoneal injection of tissue suspensions. He spoke of “masked” virus and suggested that this might represent either virus rendered inactive by combination with neutralizing substance or by alteration to a non-infective phase. Carcinomas were likewise shown...

INDUCTION OF TUMORS IN DOMESTIC RABBITS WITH NUCLEIC ACID PREPARATIONS FROM PARTIALLY PURIFIED SHOPE PAPILLOMA VIRUS AND FROM EXTRACTS OF THE PAPILLOMAS OF DOMESTIC AND COTTONTAIL RABBITS

A deoxyribonucleic acid preparation which showed infectivity and tumorigenic activity in domestic rabbits was isolated from the papillomatous tissue of wild cottontail rabbits by phenolic deproteinization procedure. The activity of the preparation could be completely abolished by its exposure to a minute amount (0.02 microg/ml) of DNAase. Antisera against Shope papilloma virus did not block the tumorigenic activity of the preparation, and trypsin and chymotrypsin had no effect on it. The extraction with phenol of a partially purified virus preparation also yielded extracts with tumorigenic potency. Extracts obtained from the domestic rabbit papilloma and submitted to phenolic deproteinization also proved infective and tumorigenic in rabbits of this sort, although the level of "tumorigenicity" was much lower than that of the cottontail preparations. Tests for intact virus, carried out with half of the extracts yielded wholly negative findings.

Ecology of Rocky Mountain Spotted Fever. I. Rickettsia rickettsii Recovered from a Cottontail Rabbit from Virginia.

SummaryFrom a naturally infected wild cottontail rabbit, S. floridanus, trapped in Virginia, an organism identified as R. rickettsii has been recovered and characterized. The role of cottontail rabbits and certain other native wild mammals in the ecology of Rocky Mountain spotted fever is discussed briefly in the light of this and other related findings.

The Life Cycle of Dirofilaria uniformis Price and Transmission to Wild and Laboratory Rabbits

Filarial worm infections available for laboratory studies have heretofore been limited to forms that are taxonomically and physiologically far removed from the Wuchereria spp. which cause human filariasis. A laboratory infection in a convenient host with a parasite more closely related to the human forms was the object of a study conducted at the Patuxent Wildlife Research Center with the cooperation of the Fish and Wildlife Service. Attention was directed toward Dirofilaria uniformis Price, 1957, a parasite of the cottontail rabbit. The life cycle of Dirofilaria scapiceps (Leidy, 1886), a related species which occurs in a capsule in the tarsal bursa of Lepus and Sylvilagus, was elucidated by Highby (1943). He named five species of Aedes from Minnesota as vectors, and successfully transmitted D. scapiceps from the snowshoe hare to domestic rabbits. The life cycle of D. uniformis has been completed with the transmission to laboratory and wild cottontail rabbits, and the results are reported here.

ORAL PAPILLOMATOSIS OF RABBITS: A VIRUS DISEASE

Papillomas occur frequently on the oral mucosa of domestic rabbits procured in the metropolitan area of New York. They are small and benign, and are situated mostly on the under side of the tongue. A filtrable virus can be extracted from them with which growths can be reproduced in the oral mucosa of several species of rabbits and hares but which fails to cause lesions when inoculated into other rabbit tissues and into the oral mucosa of other species. The virus differs notably from the Shope virus, which causes cutaneous papillomas in rabbits but proves innocuous to oral mucosa: rabbits solidly immune to the oral papilloma virus are fully susceptible to the Shope virus and vice versa. The oral papillomas are not highly contagious, for susceptible animals kept in individual cages in the same rooms with others carrying the growths, fed the same kind of food, and cared for by the same attendants, do not "catch" them. They are found much more frequently in the offspring of dams that carry the growths than in those of mothers free from them, and the causative virus can be recovered from the mouth washings of rabbits having no growths. The observations indicate that the virus may be spread by transfer from the mother to the young during the period of suckling, and that it may lie latent in the mouth, doing no harm unless the mucous membrane is injured. The slight trauma occurring now and then when coarse foods are chewed may furnish the required tissue nidus under natural conditions, for papillomas occasionally appear after virus has been dropped into the mouths of uninoculated rabbits; but the more extensive injury and healing resulting from experimental tattoo inoculations proves regularly effective in this respect. Tar can also act as an efficient adjuvant to the virus, the incidence of "spontaneous" oral papillomas being much higher in domestic rabbits that had had the opportunity to lick tar from their ears and paws during long periods than in normal control animals. The virus is recoverable in quantity from the oral papillomas of tarred domestic rabbits, and the findings indicate that it is their essential cause, the tar acting merely to prepare the tissue for the virus' action. For the same tar does not elicit oral papillomas in wild cottontail rabbits, which do not carry the causative virus though fully susceptible to it. The implications of the findings are discussed.

The Rectal Temperature and the Metabolism of the Wild Cottontail Rabbit

The Rectal Temperature and the Metabolism of the Wild Cottontail Rabbit

Carcinoma in the Cottontail Rabbit Following Spontaneous Virus Papilloma (Shope)

The Shope rabbit papilloma is an epithelial new growth caused by a filtrable virus and transmissible in series through cottontail (Genus, Sylvilagus) and domestic rabbits (Genus, Oryctolagus). Both in the gross and histologically it is similar to the virus papillomata of man, cattle and dogs., - Further, it has been found to possess not only the immediate characters of a tumor, but also the potentiality of progressive alteration until finally it may assume the characteristics of a squamous cell carcinoma with metastases., We have confirmed these findings. Carcinomatous changes have been reported previously only in experimentally inoculated domestic rabbits., , It would be highly significant were the host-parasite relationship so perfected in the natural host, the cottontail rabbit, that malignant changes never occurred. The significance of such a finding would apply irrespective of whether the virus per se, or whether secondary factors were responsible for the carcinoma. The purpose of this communication is to report that such is not the case, for we have observed carcinomatous degeneration of a naturally occurring papilloma in a wild cottontail rabbit. Of 132 cottontail rabbits (Sylvilagus floridanus alacer Bangs) received from southern Kansas, 11 have had spontaneously one or more of the papillomatous growths. These 11 cottontails were kept for observation and for a source of virus. With a single exception, our findings have agreed with those previously described., The history of the exceptional case follows: Cottontail rabbit S5-CR 363. Thin, young, adult male. Received March 30, 1935. On lower abdomen 4 pigmented warts were noted: A, 18×22×15 m. in height, B, C and D, 4-6 mm. in diameter x6-8 mm. in height. Rapid gain in weight. Papillomata appeared unchanged for 85 days, when lesion A showed superficial ulceration with thickening of the underlying tissues. Six days later the rabbit died from fracture of the lumbar spine sustained accidentally the previous day.

Serial Transmission of Virus of Infectious Papillomatosis in Domestic Rabbits

It was reported that the virus of infectious papillomatosis produced warts which were readily transmissible in its natural host, the wild cottontail rabbit. However, warts which it regularly induced in domestic rabbits were not transmissible serially in either wild or domestic rabbits. A similar situation as regards the transmission of Rous Sarcoma 1 to turkeys, guinea fowls, and pheasants has been described., The purpose of the present paper is to report the successful transmission of the virus of infectious papillomatosis serially in domestic rabbits. Warts from domestic rabbits, infected with papilloma virus of wild rabbit origin in the usual fashion, were removed at various intervals, ground with sand, suspended in physiological saline and the resulting suspension used in attempts to infect other domestic rabbits. The technique of infection was the same that had been used unsuccessfully in earlier experiments. Thirty-two attempts to carry the virus beyond its first domestic rabbit passage have been made since the 26 fruitless efforts first reported. Of these, 13 were successful, the domestic rabbits of the second serial passage developing one or more papillomas over the area of skin inoculated. Efforts to maintain the virus in domestic rabbits beyond its second serial passage were made in 7 instances and, of these, 4 were successful. Two series were carried through their fifth domestic rabbit passage and then discontinued. The remaining 2 series are still being passed; one has reached its 6th and the other its 10th domestic rabbit passage. The individual papillomas developing in rabbits infected with the domestic rabbit-passaged virus are identical in all respects with those resulting following similar infection with virus obtained from wild rabbit warts.