CHAPTER 25 Fungal Abortion
Fungi are important causes of sporadic abortion and are responsible for up to 10% of reported abortions in mares.1,2 The fungi include Aspergillus fumigatus, Mucor spp., and Allescheria boydii, with Aspergillus being the most common.2–5 Rarely reported fungi include Coccidioides immitis,6 Cryptococcus neoformans, Candida albicans, and Histoplasma capsulatum.2
MATERNAL SIGNS
Mares may display signs of estrus early in pregnancy and abort later at 8 to 11 months of gestation, usually without any premonitory signs.7 Infected mares may run milk for days before abortion and occasionally have a thick, brownish, adherent vulval discharge.1 A purulent vulval discharge may be evident for some days after abortion but resolves spontaneously.1 Infection with Aspergillus and Mucor spp. does not persist in the uterus and does not interfere with subsequent fertility.
PATHOGENESIS
Although fungal invasion of the pregnant uterus may be hematogenous or transcervical, it primarily ascends from the vagina via a patent cervix. Initially, infection begins in the chorion adjacent to the cervical star, then progresses cranially up the uterine body.1,2,7 The resultant chronic ascending chorionitis causes progressive placental insufficiency that interferes with fetal nutrition and growth and results in intrauterine growth retardation.1 Infection eventually results in abortion or premature expulsion of a dead or nonviable fetus.
FETAL MEMBRANE LESIONS
Grossly, the affected chorioallantois is diffusely involved; is yellowish, thickened, and leathery; and is clearly demarcated from the normal, reddish chorioallantois.7,8 The chorionic surface is necrotic and usually covered with thick, adherent, mucoid exudate.9 The amnion may have irregular necrotic plaques in about 10% of Mucor spp. infections.1,10 Amnionitis is not normally associated with aspergillosis.3 Microscopically, there is marked squamous metaplasia and widespread necrosis of chorionic villi and numerous hyphae are present.3,4,7
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