Kenneth W. Mills

EFFECTS OF MALATHION ON DISEASE SUSCEPTIBILITY IN WOODHOUSE'S TOADS

Adult male Woodhouses toads (Bufo woodhousi) developed clinical disease, hepatomegaly, and died at a higher rate when externally exposed once to either a high or low sublethal dose (0.011 or 0.0011 mg malathion/g toad) of field grade malathion and challenged with a sublethal dose of Aeromonas hydrophila injected intraperintoneally (1.1 × 104 bacteria/g toad) when compared to toads not exposed to malathion but challenged with A. hydrophila (P < 0.007). Toads exposed to malathion (high or low dose) and challenged with A. hydrophila had clinical disease, hepatomegaly, and died at a higher rate [9 (90%) of 10] than toads exposed to malathion alone (P < 0.002). Toads exposed to the high and low doses of malathion had a 22% and 17% decrease in brain cholinesterase levels, respectively, when they were compared to nonmalathion exposed toads (P < 0.025, P < 0.006). It appears that field grade malathion applied externally to adult Woodhouses toads may cause increased disease susceptibility when challenged with a potentially pathogenic bacteria.

CAUSES OF MORTALITY OF THE WYOMING TOAD

Wyoming toads (Bufo baxteri) that died from January 1989 to June 1996 were submitted to the Wyoming State Veterinary Laboratory (Laramie, Wyoming, USA) for postmortem evaluation. These consisted of 108 free-ranging toads and 170 animals from six captive populations. Ninety seven (90%) of 108 free-ranging toad carcasses were submitted during September and October. From 1989 to 1992, 27 (77%) of 35 mortalities in the captive populations occurred in October, November, and December. From 1993 to 1996, mortality in captive toads occurred without a seasonal pattern and coincided with changes in hibernation protocols that no longer mimicked natural cycles. Cause of mortality was determined in 147 (53%) of the 278 cases. Mycotic dermatitis with secondary bacterial septicemia was the most frequent diagnosis in 104 (71%) of 147 toads. Basidiobolus ranarum was found by microscopic examination of skin sections in 100 (96%) of 104 of these mortalities. This fungus was isolated from 30 (56%) of 54 free-ranging and 24 (48%) of 50 captive toads. This research documents the causes of mortality for both free-ranging and captive endangered Wyoming toads over a 7 yr period.

Plague in a black-footed ferret (Mustela nigripes).

Diagnosis of sylvatic plague in a captive black-footed ferret (Mustela nigripes) was based on gross and microscopic lesions, fluorescent antibody tests, culture of Yersinia pestis, and immunohistochemistry. Gross lesions consisted of acute hemorrhage and necrosis associated with cervical and mesenteric lymph nodes, subcutaneous hemorrhages, and pulmonary edema. Acute edema, hemorrhage, and necrosis with numerous bacteria in blood vessels and sinusoids characterized microscopic lesions. Occurrence of fatal plague in a black-footed ferret potentially has significant implications for recovery of this endangered species due to the widespread distribution of plague in prairie dog colonies throughout historic black-footed ferret range.

Laboratory findings associated with abomasal ulcers/tympany in range calves

The etiology of abomasal ulcers/tympany was investigated in 48 animals from 36 ranches in Wyoming and Nebraska. Results indicate that subclinical trace mineral deficiencies of copper and/or selenium exist in the range cattle in west central Nebraska and Wyoming. Etiological agents most frequently incriminated by bacteriologic cultures and/or histopathic examination were Clostridium perfringens and Campylobacter species. Histopathologic evaluation of abomasums revealed 31 of 38 cases contained abundant gram-positive bacteria associated with the damaged abomasal mucosa. Campylobacter-like organisms were demonstrated in 9 of 38 cases using the modified Dieterle stain. Clostridium perfringens was isolated in 14 of 38 cases, and Campylobacter jejuni was recovered from 5 of 38 cases.

ASSOCIATION OF MORAXELLA OVIS WITH KERATOCONJUNCTIVITIS IN MULE DEER AND MOOSE IN WYOMING

Six cases of infectious keratoconjunctivitis (IKC) in mule deer (Odocoileus hemionus) and moose (Alces alces) in Wyoming (USA) were investigated during fall and winter of 1995 and 1996. Excessive lacrimation, mucopurulent conjunctivitis, keratitis, and corneal opacity were observed in mule deer. Moose had severe mucopurulent conjunctivitis, keratitis, and corneal ulceration. Hemolytic, non-piliated Moraxella ovis was isolated from two mule deer and two moose. We attempted to reproduce IKC in three mule deer fawns using an isolate of M. ovis from a clinically affected mule deer. These fawns did not develop clinical signs of infection and the bacterium was not reisolated from inoculated deer. Inoculated deer may not have developed clinical signs because deer were not exposed to ultraviolet light or mechanical insult before inoculation. In addition, the isolate used for inoculation may have lost virulence factors through passage, or M. ovis may not have been the primary pathogen responsible for clinical disease in the natural cases of IKC we investigated. The etiology of IKC in free-ranging wild ruminants remains poorly understood.

Mortality of Captive Canadian Toads from Basidiobolus ranarum Mycotic Dermatitis

Twenty-six adult free-ranging Canadian toads (Bufo hemiophrys) were collected from northeastern North Dakota (USA) during the last week of August 1994 and placed in captivity. During late December and January 1995, 21 Canadian toads died. Clinical signs included increased time sitting in water bowls, darkened dorsal skin, constant arching of their backs, and hyperemia and sloughing of ventral epidermis. The condition progressively worsened until death occurred within 5 to 7 days after onset of clinical disease. Mycotic dermatitis due to Basidiobolus ranarum was diagnosed in all toads and the fungus was isolated from 11 (52%) of 21 toads. Histology of the ventral skin and digits revealed numerous fungal spherules and occasional hyphae without significant inflammatory reaction. This condition clinically resembled red leg associated with Aeromonas hydrophila and many other bacterial organisms, and the diseases could be confused without appropriate diagnostic tests. This also is the first report of B. ranarum causing clinical disease in a toad species.

Experimental exposure of Canadian toads to Basidiobolus ranarum.

Experimental transmission of the fungus Basidiobolus ranarum was induced in two treatment groups of Canadian toads (Bufo hemiophrys) and caused a fatal mycotic dermatitis. Seven of 10 (70%) toads that had their ventral skin mildly abraded and exposed to B. ranarum developed hyperemia, and sloughing of their ventral skin and died. Toads with abraded ventral skin or exposure to infected skin also were affected statistically at a higher rate than those with abraded skin and exposure to pure cultures of B. ranarum innoculated into their water source. Of toads showing clinical disease, B. ranarum was identified by both impression smears and histology in all cases, but not from toads that appeared clinically healthy. The organism was cultured from 5 of 7 (71%) toads with clinical disease but not from any toad that appeared clinically healthy (n = 28). This study documents methods of experimental transmission of B. ranarum, an organism responsible for causing a mycotic dermatitis that is fatal to toads.

Mucormycotic Dermatitis in Captive Adult Wyoming Toads

During late May 1995, 50 adult captive endangered Wyoming toads (Bufo baxteri) were brought out of hibernation. Approximately 3 to 10 days after hibernation emergence, all toads were hormonally induced to breed, and paired. Each pair was placed in their own breeding tank. Four toads developed clinical signs of disease which included lethargy and multiple (4 to 12) small (2 mm) raised hyperemic nodules with white fuzzy caps on the ventral skin. The condition progressively worsened until death occurred, within 3 to 6 days. Mycotic dermatitis caused by Mucor sp. was diagnosed in the four toads through histology and isolation of the organism. This is the first case report of a Mucor sp. causing a fatal dermatitis in an amphibian without significant inflammatory response and without systemic involvement.

Tularemia in range sheep : an overlooked syndrome?

Abortion and death caused by Francisella tularensis were well recognized in range flocks of domestic sheep in Idaho, Montana, and Wyoming in the first 6 decades of the 20th century. The current report describes 4 episodes of tularemia in 3 range flocks in Wyoming and South Dakota in 1997 and 2007 (1 flock was affected twice). Flock owners reported that ticks were unusually numerous and commonly present on sheep during outbreaks. Tularemia presented as late-term abortions (3 episodes) or listlessness and death in lambs and, to a lesser extent, ewes (1 episode). Lesions were multifocal pinpoint necrotic foci in tissues, particularly spleen, liver, and lung. An immunohistochemical procedure demonstrated F. tularensis, particularly in necrotic foci. The diagnosis was corroborated by bacterial isolation and, in individual cases, by serology, fluorescent antibody assay, and/or polymerase chain reaction detection of F. tularensis. Diagnosticians in endemic areas should include tularemia as a differential diagnosis when investigating late-term abortions or outbreaks of fatal illness in young lambs, particularly in years of high tick activity and when characteristic necrotic foci occur in spleen, liver, and lung.

Bacteria and nematodes in the conjunctiva of mule deer from Wyoming and Utah.

Swabs of conjunctiva were collected from 44 live and 226 hunter-harvested mule deer (Odocoileus hemionus) from Wyoming and Utah (USA). We identified 29 Gram negative and 22 Gram positive bacterial taxonomic categories, but many isolates from hunter-harvested animals were environmental contaminants. Staphylococcus spp. and Micrococcus spp. were the most common Gram positive bacteria isolated, and Enterobacter spp., Escherichia coli, and Pseudomonas spp. were common Gram negative bacteria isolated. Thelazia californiensis were found in 15% of hunter-harvested deer in Utah in 1994 and in 8% in 1995. Nematodes were found in 40% of live deer in 1995 and 66% in 1996. Three live animals showed clinical signs of infectious keratoconjunctivitis (IKC) in 1996, but pathogenic bacteria were not isolated from these individuals. Hemolytic, non-piliated Moraxella ovis was isolated from two clinically normal live deer in 1996 and isolates were similar to those cultured from IKC cases from Wyoming and Utah.