Prominent animal mycoses from various regions of the world.

The mycoses selected for presentation in this section are relatively common diseases of companion animals or livestock in certain areas of the world. Malasseziosis is arguably the most frequent mycosis of dogs (as otitis externa and dermatitis) throughout the world, although its diagnosis is often overlooked. Protothecosis is also geographically widespread, particularly in cattle where severe mastitis is a result of adventitious infection from the environment. In contrast, coccidioidomycosis and pythiosis are geographically limited in their occurrence (coccidioidomycosis by geographic region and pythiosis by climate), but within regions where they do occur, their presence in animals is not unusual. It was our intention to review recent developments in each of these diseases.

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.

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.

Parasitic relationship between Microsporum canis and the cat.

Cats are often cited as reservoirs of M. canis but it is questionable whether M. canis is part of the resident flora of the cat's skin and hair or only a transient organism. Studies indicate that M. canis is most often isolated from cats at risk of infection or exposure from other infected cats or from a contaminated environment. Many more cats are culture-positive for M. canis than have dermatophytosis. Culture isolation alone is not an indication of dermatophytosis; the diagnosis of dermatophytosis requires microscopic evidence of infection as well as culture evidence of the presence of the dermatophyte. The cat's hair coat adopts the culture image of its surroundings. Diverse factors may influence the frequency of isolation of M. canis. Nevertheless, isolation of M. canis implies either active disease or fomite carriage and warrants aggressive investigation of the clinical situation.

Experimental immunity to Microsporum canis and cross reactions with other dermatophytes of veterinary importance.

An inactivated, broad-spectrum dermatophyte vaccine was used to produce an active immunity in guinea-pigs against Microsporum canis. None of the vaccinates developed infection from a contact exposure challenge that produced clinical infections in 70% of the unvaccinated controls. Infection with M. canis induced antibody titres (ELISA) and delayed cutaneous hypersensitivity (DCH) reactions to itself as well as cross-reacting titres to Trichophyton equinum and T. mentagrophytes and DCH reactions to T. mentagrophytes; however vaccinated animals developed significantly higher antibody titres and DCH responses to all of these antigens than did non-vaccinated animals which had been infected or exposed. Rabbits hyperimmunized with culture filtrate antigens to single dermatophyte agents (M. canis, M. gypseum, T. equinum, and T. mentagrophytes) developed positive inter-species and inter-generic DCH cross-reactions to a battery of six skin test antigens (M. canis, M. gypseum, M. equinum, T. equinum, T. mentagrophytes var. mentagrophytes and T. verrucosum). Guinea-pigs vaccinated with a T. equinum vaccine had increased resistance to M. canis infection than did non-vaccinated controls. These findings support clinical observations which suggest establishment of a broad-based immunity in animals following infection with a single dermatophyte.

Major biological consequences of aflatoxicosis in animal production.

Aflatoxins, a family of closely related, biologically active mycotoxins, have been known as a prominent cause of animal disease for 30 yr. The toxins occur naturally on several key animal feeds, including corn, cottonseed, and peanuts. Occurrence of aflatoxin on some field crops tends to spike in years when drought and insect damage facilitate invasion by the causative organisms, Aspergillus flavus and A. parasiticus, which abound in the crop's environment. Acute aflatoxicosis causes a distinct overt clinical disease marked by hepatitis, icterus, hemorrhage, and death. More chronic aflatoxin poisoning produces very protean signs that may not be clinically obvious; reduced rate of gain in young animals is a sensitive clinical register of chronic aflatoxicosis. The immune system is also sensitive to aflatoxin, and suppression of cell-mediated immune responsiveness, reduced phagocytosis, and depressed complement and interferon production are produced. Acquired immunity from vaccination programs may be substantially suppressed in some disease models. In such cases the signs of disease observed are those of the infectious process rather than those of the aflatoxin that predisposed the animal to infection. Mixtures of aflatoxin with other mycotoxins can result in greatly augmented biological responses in terms of rate of gain, lethality, and immune reactivity. Because of its great biological activity, its wide-spread potential presence in areas where critical feed crops are grown, and its propensity to spike in problem years, aflatoxin promises to be a continuing problem in animal production.

Effects of cyclopiazonic acid and aflatoxin singly and in combination on selected clinical, pathological and immunological responses of guinea pigs.

Cyclopiazonic acid (CPA) and aflatoxin are known sometimes to coexist in nature but little is known of possible biological interaction in mammals that consume mixtures of these two mycotoxins. Guinea pigs were dosed orally with CPA (2.2 mg/kg) or aflatoxin (0.045 mg B1/kg) singly or in combination. Effects of toxin consumption were determined on clinical health, body weight gain, pathological change, and several immunologically related parameters including delayed cutaneous hypersensitivity, antibody response, complement hemolytic titer, intracutaneous mitogen (PHA) and in vitro lymphocyte blastogenesis. In contrast to an earlier study by others, significant synergy between these two toxins was demonstrated in reduced rate of body weight gain, lethality and histologic changes (vacuolization) in hepatocytes. Reductions in complement titer, intradermal PHA, delayed cutaneous hypersensitivity response and in vitro lymphocyte blastogenesis were related to aflatin activity. No effects on antibody formation to Brucella abortus were observed with either toxin or the combination of toxins. Cyclopiazonic acid appeared to restore the suppressive effects of aflatoxin in delayed cutaneous hypersensitivity response and in vitro lymphocyte blastogenesis.

Evaluation of histopathologic and physiologic changes in cows having premature births after consuming Ponderosa pine needles.

Premature calving, typified by early expulsion (17 to 43 days) of weak or dead calves and accompanied by retained placentas, was induced in 8 of 9 pregnant cows fed a mixture of Ponderosa pine needles and alfalfa hay. Five control cows of comparable gestation age fed only alfalfa hay maintained normal pregnancies until they were euthanatized at the time the pine needle-treated cows were producing premature calves. Serum specimens from all cows were assayed for progesterone concentration and ovaries and placentomes were examined for histopathologic changes. There were no bacterial, fungal, chlamydial, or viral agents determined to be associated with the premature births. Serum progesterone concentration in the treated cows decreased progressively and were 0.4 to 1.5 ng/ml at the time of premature calving. Histopathologic changes were evident in the placenta and corpora lutea of treated cows only. The number of binucleate trophoblastic giant cells in placentomes was less than normal and the number of necrotic luteal cells in corpora lutea was greater than normal.

Use of bacteria and yeasts to identify T lymphocytes in peripheral blood and lymphoid tissues of healthy guinea pigs and guinea pigs fed aflatoxin.

Fifty-four bacterial and 10 yeast isolates were screened to identify strains that were consistently bound by peripheral blood lymphocytes (PBL) of guinea pigs. None of the yeast isolates examined was bound by guinea pig PBL. Of 54 bacterial isolates, 10 were bound by greater than 5% of PBL. Potential lymphocyte markers from these bacteria were chosen for further study. Sodium azide inhibited the binding of bacteria by PBL. Preparations of T lymphocytes indicated that Salmonella schottmuelleri was bound by most T lymphocytes; Yersinia enterocolitica was bound by a subpopulation of T lymphocytes. Patterns of binding of bacteria by lymphocytes from thymus, lymph node, or spleen differed from binding patterns obtained using PBL. Aflatoxin did not affect the total WBC, differential leukocyte count, absolute lymphocyte count, or relative percentage of PCV of guinea pigs given as much as 0.060 mg of aflatoxin B1 equivalents/kg of body weight/day for 3 weeks. Changes in absolute numbers of peripheral blood T lymphocytes were not observed in guinea pigs given aflatoxin when immunofluorescence or bacterial binding was used to identify lymphocyte populations, except that the number of S schottmuelleri-binding lymphocytes (tentatively identified as T lymphocytes) in guinea pigs given the highest dose of aflatoxin (0.060 mg of aflatoxin B1 equivalents/kg/day) was less than the number of T lymphocytes identified by immunofluorescence.

Fate of aflatoxins in tissues, fluids, and excrements from cows dosed orally with aflatoxin B1.

A study was conducted to determine aflatoxins in tissues and non-tissues of 2 Holstein cows given oral doses of 0.35 mg of purified aflatoxin B1/kg of body weight/day for 3 consecutive days. Cow 1 was slaughtered 24 hours after the 3rd dose, and cow 2, after day 3, was fed aflatoxin-free rations for 7 additional days before slaughter. Tissue samples of brain, gallbladder and bile, heart, intestine, kidney, liver, lung, mammary gland, skeletal muscle, spleen, supramammary lymph nodes, thymus, and tongue, and nontissue samples of blood, feces, milk, rumen content, and urine were examined. Aflatoxins B1 and M1 were found in all samples of cow 1, except the thymus. Kidney, liver, and mammary gland had the highest concentrations of total aflatoxins (57.9, 13.2, and 25.1 ng/g, respectively), with the aflatoxin M1 concentration 40 times more than the aflatoxin B1 level in kidney. Aflatoxin residues were present (0.02 to 0.11 ng/g) only in kidney, liver, and intestine of the tissues from cow 2 (fed aflatoxin-free feed for 7 additional days). Aflatoxin B1 was not present in nontissue samples, but aflatoxin M1 (0.10 and 1.5 ng/ml) was found in the last milk and urine samples from the same cow. Urine assays are a possible way to monitor the presence of aflatoxin residues in meat tissues.

Effect of feeding corn naturally contaminated with aflatoxin on feed efficiency, on physiologic, immunologic, and pathologic changes, and on tissue residues in steers.

Two of 3 groups of Holstein-Friesian steers (groups II and III; n = 5 each) were fed a ration containing corn naturally contaminated with 800 ng of aflatoxin/g. The other group of steers (group I; n = 5) was fed a ration containing noncontaminated corn. The respective rations were fed for 17.5 weeks, except the ration given to group III; the latter's first diet (contaminated with aflatoxin) was changed to a noncontaminated diet after 15 weeks, continuing for the remaining 2.5 weeks. All steers were killed and tissues and fluids were obtained for aflatoxin analysis. Although aflatoxin B1 and M1 could be detected in blood and urine at several sampling times during the experimental period in groups II and III steers (given the diets containing aflatoxin), there appeared to be no effects on body weight gains and immune phenomena, such as lymphoblastogenesis and antibody production, but there was a waning of the delayed cutaneous hypersensitivity in steers given aflatoxin-contaminated diets. In group III animals (diet was changed to noncontaminated ration at 15 weeks), aflatoxin B1 and M1 disappeared from urine before they were slaughtered. All tissues and fluids, except the rumen contents from these group III steers, were void of detectable aflatoxins B1 and M1 at necropsy. The concentrations of aflatoxin B1 in the rumen content of the latter steers were low. All tissues collected at necropsy from the group II steers fed the aflatoxin diet throughout the 17.5 weeks had detectable aflatoxins B1 or M1 present.

Counterimmunoelectrophoresis (immunoelectroosmosis) and serum electrophoretic pattern in serologic diagnosis of canine blastomycosis.

Counterimmunoelectrophoresis (CIEP) with blastomyces and histoplasma antigens was used in a serologic study of 181 dogs clinically suspected of having blastomycosis and of 8 dogs with confirmed blastomycosis or histoplasmosis. Thirteen of the 181 dogs, positive by CIEP, were euthanatized, and the diagnosis was confirmed by cultivation and/or microscopic detection of Blastomyces dermatitidis. Additional CIEP-positive dogs were confirmed by staining of aspirates collected in vivo. Radiographic support for the diagnosis was reported in 4 other dogs in which histoplasmosis was excluded by a negative CIEP with histoplasma antigen. The precipitating antibody may disappear during the course of the disease, as it did in 1 dog treated with amphotericin B, but not cured. This dog reverted from CIEP-positive to CIEP-negative within 17 months of treatment (with a weak reaction after 10 months of treatment). The CIEP-detectable antibody was present only in 1 dog without a confirmation by histopathologic findings or cultivation among 24 well-documented cases and 181 total tested sera. The CIEP was more sensitive and specific than was the gel-diffusion precipitin test, eliminated the problems of anticomplementarity that often affected the results of complement-fixation tests with canine sera, and served well in detecting dogs with blastomycosis. Electrophoretic pattern of sera from CIEP-positive dogs with blastomycosis showed a decrease in albumin and an increase in alpha 2- and often in beta- and gamma-globulins, with a substantial decrease of the albumin/globulin ratio.

Vaccination studies of aspergillosis in turkeys: subcutaneous inoculation with several vaccine preparations followed by aerosol challenge exposure.

Five vaccines were prepared from an isolate of Aspergillus fumigatus: a culture filtrate vaccine (I), a spore vaccine (II), a mycelial vaccine (III), and 2 germling vaccines (IV and V). The 2 germling vaccines were produced on different media. Two experiments were conducted to test the vaccines for efficacy in groups of 21 turkey poults by giving each bird 2 subcutaneous inoculations of the respective vaccine at 1 and 2 weeks of age. The birds were challenge exposed to an aerosol of spores of A fumigatus at 1 month of age. The 2 experiments differed only in the challenge exposure. In experiment 1, 38% of the poults were protected when vaccinated with an A fumigatus germling vaccine (IV) and challenge exposed with a dose of aerosolized A fumigatus spores that killed 100% of the nonvaccinated controls. Onset of postchallenge-exposure deaths were delayed by 2 days in the turkeys given vaccine IV. In experiment 2, 48% of the poults were protected when given germling vaccine IV, whereas 62% to 86% of the poults in the nonvaccinated and 3 other vaccine groups died. In experiment 2, 50% of the poults given a mycelial vaccine (III) were protected. Torticollis was a frequent sign of the disease in experiment 2.

Determination of sensitivity and specificity of the Nocardia asteroides skin test for detection of bovine mammary infections caused by Nocardia asteroides and Nocardia caviae.

A total of 116 cows from 4 dairy herds in California were used to determine the sensitivity and specificity of extracellular antigen of Nocardia astero des for possible detection of bovine mastitis caused by N asteroides and N caviae. Three different positive criteria were used. These criteria gave different sensitivity and specificity to the skin test. The highest sensitivity of 80% and highest specificity of 96.04% were obtained by combining 2 criteria. The study found no cross-reaction between N asteroides antigen and Mycobacterium fortuitum or N asteroides and tuberculin skin tests. There was cross-reaction between N asteroides antigen and N caviae infection.