Here is a sneak preview of the forthcoming book Current Therapy in Equine Medicine, 5th Edition. The following chapteron Molds and Mycotoxins is by Mike Murphy.

MOLDS AND MYCOTOXINS

Mike Murphy

St. Paul, Minnesota

Moldy feed is a perceived problem with many horse owners.They may believe that all airborne particulate matter that arisesfrom their feed or hay source is mold. In many instances thisairborne particulate matter is dust from dry soil, grain, plant orinsect matter. This chapter focuses on those instances in whichthe material is in fact the vegetative or spore form of a mold ormolds.

All molds do not produce mycotoxins. Horses may expe-rience mold-associated disease in the categories of mycoses,allergies, or mycotoxicoses. This chapter focuses on mycosesand allergies. Subsequent chapters and those in previous edi-tions of this series discuss the mycotoxicoses.

Tables 15.8-1 lists molds that have been reported in dif-ferent organ systems of horses, and Table 15.8-2 provides a listof molds and mycotoxins that affect horses.

MOLD-INDUCED DISEASES

A number of diseases in horses have been associated withthe presence of molds. These diseases, or mycoses, involveguttural pouches, lungs, eyes, skin, the reproductive system,and the body as a whole.

Guttural Pouch MycosisMolds have been isolated from infected guttural pouches

in horses worldwide. Erosion of the internal carotid artery,cranial nerve damage, or blindness may follow guttural pouchmycoses (see Chapter 7.7: “Guttural Pouch Disease”). Themost common molds isolated from equine guttural pouches areAspergillus, Penicillium, and Candida. Aspergillus nidulans isthe Aspergillus species most commonly isolated from equineguttural pouches. Aspergillus nidulans has recently been re-named Emericella nidulans.

The association between Aspergillus nidulans and guttural

pouch mycosis was first recognized in the early 1970s. Soonthereafter an association between Aspergillus nidulans gutturalpouch mycosis and nosebleeds was made. Horses have bled todeath after erosion of the carotid artery because of Emericellanidulans infection of the guttural pouch.

Two other species of Aspergillus are commonly isolatedfrom equine guttural pouches. Aspergillus fumigatus from aguttural pouch infection has caused an atlantooccipital jointinfection and nasal discharge. Guttural pouch mycosis has alsobeen caused by Aspergillus ochraceus. A Penicillium sp. moldwas isolated from the guttural pouch of a horse with a fistulathat developed from a guttural pouch mycosis.

LungsAspergillus organisms have also been associated with lung

lesions in horses. Both acute and chronic forms of the diseasehave been identified. An association between GI disease andpulmonary Aspergillosis has also been suspected. Invasivepulmonary aspergillosis has been identified in 19 horses; 16 ofthem also had enterocolitis. Endocarditis, apathy, fever, lacri-mation and dyspnea with thrombosis, hemorrhage and tissuenecrosis have been associated with Aspergillus niger. Thesudden death of two horses was attributed to the rapid andacute development of pulmonary aspergillosis.

EyesA variety of molds have been isolated from the eyes of

horses with keratitis. Alternaria, Aspergillus, Actinomyces,Candida, Fusarium, Penicillium, Mucor, Rhizopus, Cephalo-sporium, and Phycomyces organisms have all been isolated.Aspergillus, Fusarium and Penicillium organisms seem to bethe most prevalent. Aspergillus flavus, A. fumigatus, and As-pergillus oryzae are the most commonly reported Aspergillusspecies.

Reproductive SystemMolds are rarely associated with abortions or with uterine

or placental infections in horses. Candida tropicalis, A. fumiga-tus, Candida albicans, Cryptococcus laurentii, Mucor (3), As-

Reprinted with permission.Copyright 2002, Elsevier Science (USA). All rights reserved.0737-0806/02/2209-0008$35.00/0doi:10.1053/jevs.2002.37241

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pergillus (2), and Microsporum (1). A. fumigatus has beendiagnosed as the cause of abortion in two Thoroughbred mares.

A. fumigatus and Candida albicans have been isolatedfrom mares with uterine infections. Fungi isolated from theuteri of mares with endometritis are Actinomyces, Aspergillus,Candida, Coccidioides, Hansenula, Monosporium, Mucor, No-cardia, Paecilomyces, and Trichosporon organisms. Of 27mares with chronic infertility problems, Alternaria sp., As-pergillus flavus, A. fumigatus, A. niger, Mortierella wolfii, and

Mucor sp. were isolated from cervical, vaginal, or clitoral fossaswabs. Of 200 cases of infective placentitis, 37 were caused byA. fumigatus and 14 by Absidia sp.

SkinOf 1090 horses examined, most had Trichophyton equi-

num skin disease, but Aspergillus infection was common.

SepticemiaAn 18-year-old Morgan had a 10-day history of watery

diarrhea, depression, and dysphagia. It died 4 days after beingreferred to a veterinary teaching hospital. A. niger was identi-fied as the cause of vasculitis and brain infarction. Mucor andRhizopus organisms were associated with a horse that devel-oped myocarditis and nephritis after surgery.

ImmunosuppressionHorses have rarely developed systemic mold infections

after corticosteroid treatment or natural immunosuppression.Fatal pulmonary infections with A. flavus and A. niger devel-oped after corticosteroid immunosuppression or colic treat-ment. Two horses with myelomonocytic leukemia developedpulmonary aspergillosis. A chronic bronchopulmonary As-pergillus infection was diagnosed in a 30-year-old Saddlebredwith Cushing’s syndrome.

MOLD ALLERGIES

Heaves—also called recurrent airway obstruction (RAO),chronic obstructive pulmonary disease (COPD), “brokenwind,” or “pulmonary emphysema” (see Chapter 8.4: “Heaves[Recurrent Airway Obstruction]: Practical Management ofAcute Episodes and Prevention of Exacerbations”)—is achronic inflammatory obstructive airway disease. Current evi-dence indicates that heaves is a delayed hypersensitivity re-sponse to inhaled antigens, particularly molds. Although horses

Table 15.8-1. Molds that have been reported in differentorgan systems of horses.

Mold System/Disease

Absidia organisms ReproductiveActinomyces organisms Eyes

ReproductiveAlternaria organisms Eyes

ReproductiveAspergillus organisms Eyes

Guttural pouch diseaseLungsReproductiveSkin

Aspergillus flavus EyesReproductiveSepticemia

Aspergillus fumigatus COPDEyesGuttural pouch diseaseReproductive

Aspergillus nidulans Guttural pouch diseaseAspergillus niger Lungs

ReproductiveSepticemia

Aspergillus ochraceus Guttural pouch diseaseAspergillus oryzae EyesCandida organisms Eyes

Guttural pouch diseaseReproductive

Candida albicans ReproductiveCandida tropicalis ReproductiveCephalosporium organisms EyesCladosporium organisms EyesCoccidioides organisms ReproductiveCryptococcus laurentii ReproductiveEmericella nidulans Guttural pouch diseaseFusarium organisms EyesHansenula organisms ReproductiveMicropolyspora faeni COPDMicrosporum organisms ReproductiveMortierella wolfii ReproductiveMucor organisms Eyes

ReproductiveSepticemia

Nocardia organisms ReproductivePaecilomyces organisms ReproductivePenicillium organisms Eyes

Guttural pouch diseasePhycomyces organisms EyesRhizopus organisms SepticemiaRhizopus stonifer Eyes

LungsTrichophyton equinum SkinTrichosporon organisms Reproductive

COPD, Chronic obstructive pulmonary disease.

Table 15.8-2. Molds and mycotoxins that affect horses.

Mold Source Mycotoxin

Aspergillus coenophialum Fescue ErgovalineAspergillus organisms Grain AflatoxinClaviceps purpura Small grains ErgotFusarium organisms Grain DeoxynivalenolFusarium moniliforme Grain FumonisinNeotyphodium coenophialum Fescue ErgovalinePenicillium Grain AflatoxinRhizoctonia leguminicola Legumes Slaframine

408 JOURNAL OF EQUINE VETERINARY SCIENCE

with heaves have strong skin reactions after intradermal injec-tions of mold extracts, more recent studies of dermal andpulmonary reactivities to Micropolyspora faeni, A. fumigatus,and T. vulgaris indicate that intradermal testing is of limitedvalue in investigating heaves.

Studies of serum antibody titers have been equally disap-pointing. Circulating precipitins to M. faeni and A. fumigatusare not restricted to horses with heaves, although they do occurmore frequently in horses with heaves.

The use of bronchoalveolar lavage fluid (BALF) has re-cently shed light on the pathogenesis of heaves. M. faeni and A.fumigatus have been identified as common causes of respira-

tory hypersensitivity in horses affected with heaves. An en-zyme-linked immunosorbent assay (ELISA) was used to mea-sure specific antibodies to M. faeni and to A. fumigatus in theserum and BALF of normal horses, horses with heaves, andhorses with other respiratory diseases; elevated antibody resultswere not detected in the sera of any horses, but IgE and IgAantibodies to both allergens were significantly elevated in theBALF of heaves-affected horses. Horses with heaves havesignificantly higher concentrations of IgE and IgG directed toA. fumigatus antigens in BALF even though they have nosignificant differences in serum.

Treatment of heaves is described in Chapter 8.4.

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