In the summer of 2008, Heeke ADDL was presented with a one-year old female Boer goat with a two day history of anorexia, "drunken" staggering, weakness, glass-eyed appearance, and lateral recumbency.  Five out of 20 goats in this herd had died with similar clinical signs.  The goats had been purchased four months prior to the onset of illness, had been treated with anthelminthic 2 weeks prior to submission, and anthelminthic treatment was repeated on the day prior to submission.  The diet consisted of grass hay and a grain supplement (Goat Chow).  No silage was fed.

At submission, the goat was alive but moribund in lateral recumbency.  The animal was in good nutritional condition with adequate muscling and body fat.  Fecal flotation revealed high numbers of Hemonchus contortus ova and high numbers of coccidial oocysts.  The blood had a packed cell volume of 26%.  Following physical examination, the goat was humanely euthanized and necropsied.

Grossly, the goat had mild meningitis, mild bronchopneumonia, and mild abomasal hemonchosis.  The meningitis was characterized by slight reddening, unusual wetness, and slight cloudiness of the meninges overlying the cerebellum and the caudal brain stem.  The bronchopneumonia affected only the tip of the right cranial lung lobe which was red-gray and firmly consolidated.  The abomasum contained a small amount of red-brown watery fluid, and low to moderate numbers of Hemonchus-like nematodes.  Grossly, the goat did not appear anemic.  The rumen was filled with finely ground grassy forage and a few fragments of broadleaves.  Intestines were unremarkable and the rectum contained normal firm fecal pellets.  Cytological impression smears of brain stem meninges had increased numbers of neutrophils, consistent with mild suppurative meningitis.

Histologically, the medulla oblongata, cerebellar peduncle, and midbrain had multifocal suppurative encephalitis.  Scattered mild neutrophilic infiltrates were also present in the meninges.  No histologic lesions were present in the thalamus and cerebral cortex.

Bacterial cultures isolated Listeria monocytogenes from the brain stem and Mannheimia haemolytica from the lung.  Serologic tests were negative for caprine arthritis encephalitis (CAE).

Although the clinical history in this case initially suggested parasitism, the final diagnosis was primary encephalitis listeriosis, complicated by concurrent abomasal hemonchosis and pneumonic pasteurellosis.  Because of similar clinical presentation, it was assumed by the owner that all six of his dead goats had died of listeriosis, but the cause of death in the remaining animals was never confirmed and we cannot exclude the possibility that parasitism contributed to some of those deaths.  The persistence of Hemonchus in the face of repeated worm medication is indicative of anthelminthic resistance.

Listeria is a common cause of encephalitis in all ruminants, and most large animal practitioners are familiar with it in cattle.  This case illustrates a number of observations about caprine listeriosis that differ slightly from bovine listeriosis, and these differences are further examined in an epidemiologic review of ADDL records below.

ADDL pathology records for the past 5 ½  years (2004-2009) reveal that caprine encephalitic listeriosis has been diagnosed 42 times (25 at the West Lafayette lab, 17 at Heeke lab).  In comparison, bovine encephalitic listeriosis has been diagnosed only 29 times (16 at West Lafayette, 13 at Heeke lab).  Since our overall cattle submissions outnumber goat submissions, the higher incidence in goats suggest that goats are more susceptible to listeriosis.  Increased susceptibility in goats is also suggested by the epidemiologic data within the submitting herds.  Available submission forms and case records for the Heeke lab submissions (17 caprine, 12 bovine) were pulled and tabulated (see tables at end of article).  Of the 17 caprine cases, four (24%) involved outbreaks of three or more animals in the flock,, five (29%) involved two animals, and eight (47%) involved only one animal at the time of submission.  In contrast, of the 12 bovine cases, none (0%) involved three or more animals, three (25%) involved two animals, and nine (75%) involved only one animal at the time of submission.  Thus, goat herds appear more likely to suffer listeriosis outbreaks that involve multiple animals.

Bovine listeriosis is often associated with the feeding of silage, presumably spoiled silage.  As in the case reported here, almost all cases of caprine listeriosis that we have seen do not involve the feeding of silage.  Dietary information was provided for eight of the Heeke lab goat submissions and, in all eight cases, silage was not a part of the diet (0% feeding silage).  In contrast, dietary information provided for 10 of the bovine cases suggested that seven (70%) of those cases were associated with silage feeding.  The source of infection in the goat cases is undetermined, but is presumed to be spoiled hay or feed that has been contaminated with dirt or feces, as the natural reservoir for Listeria monocytogenes appears to be soil and mammalian GI tracts.  One previous study found that listeriosis was more prevalent in goats that browsed heavily, as compared to goats consuming hay or pasture (Johnson, 1996).  Our data provided no information about browse patterns.  Another study has suggested that venereal transmission may occur in goats (Wiedmann).

Merningitis was grossly visible in this case and, in my experience, is much more likely to be present in cases of caprine listeriosis.  In contrast, meningitis is seldom noticeable in cases of bovine listeriosis.  Gross meningitis was reported in six (35%) of the caprine cases, but it was reported in only one (8%) of the bovine cases.  Although meningitis was more frequently seen in goats, it is still not a reliable diagnostic finding.  Interestingly, grossly visible encephalitis (focal hemorrhage and necrosis of the brain stem) was more frequently reported in the bovine cases.  Four (31%) of the bovine cases reported grossly visible encephalitis, whereas none (0%) of the goat cases had grossly visible encephalitis.

It has been my impression that Listeria monocytogenes  is more easily isolated from the brains of affected goats, and a previous study suggests this may be true (Johnson, 1995).  Our records show a similar tendency, though less dramatically.  Listerial cultures were attempted in 14 of the goat cases and 10 bovine cases, and it was successfully isolated from four (29%) of the affected goat brains, and from two (20%) of the affected bovine brains.  In a fifth goat case, we isolated an unidentified Corynebacterium-like species.  Although this isolate differed biochemically from the usual strains of Listeria monocytogenes, positive immunohistochemistry results suggested that it was antigenically related to Listeria.  In one bovine case, we failed to isolate Listeria, but Brevibacillus borstelensis was isolated from the brain.  The histologic lesion in this case was typical of listeriosis, but it is possible that Brevibacillus was the actual cause of the lesion.    In both species, bacterial culture continues to be a relatively unreliable diagnostic procedure for encephalitis listeriosis.  The poor rate of isolation may be due to prior treatment with antibiotics, as most of these animals had reportedly been treated prior to death.

In our laboratory, most cases of listeriosis are diagnosed by histopathology  and, of the traditional diagnostic procedures, histopathology continues to be the most reliable method of diagnosis for encephalitic listeriosis.  Formalin fixed sections of brain stem are the preferred sample to submit.  (Please remember that Listeria lesions occur only in the brain stem, and submission of cerebral cortex may provide false negative results).  Several newer and more sensitive diagnostic procedures are also available at ADDL.  As mentioned above, we can diagnosis listeriosis by immunohistochemistry (IHC) and the preferred sample again is a formalin-fixed section of brain stem.  A previous study found that IHC was much more sensitive than bacterial culture (Johnson, 1995).  In addition, our molecular diagnostics lab can now diagnose listeriosis by PCR analysis.  For this, the preferred sample would be a segment of fresh (unfixed) brain stem.

Our data provided no information about treatment of listeriosis, but treatment is often unrewarding due to the difficulty of getting therapeutic levels to the brain.  Nevertheless, one previous study reported that, of nine animals treated with a combination of gentamicin and ampicillin, six survived (Braun).

Photos provided by Dr. Jose Ramos-Vara
Detail of immunohistochemical staining.  There are numerous labeled bacteria within hepatocytes.  Immunoperoxidase- DAB for Listeria sp.	Listeriosis. Liver.  Dark shading  (brown) indicates the presence of Listeria antigen within necrotic foci.  Immunoperoxidase-DAB for Listeria sp.
Corynebacterium sp. (biochemically different from Listeria) was isolated from one brain, but the brain stained positive for Listeria by immunohistochemistry. ** In all cases, listeriosis was diagnosed by histopathology.

-by Dr. Duane Murphy, ADDL PathologistHeeke ADDL

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