Brown Antechinus (Antechinus stuartii) with multiple parasites and presumed herpesvirus

Registry Case Number TARZ-9449.1

An adult male Antechinus (weight 4.3g) was captured overnight in an Elliott trap in Ku-ring-gai Chase National Park during annual, routine wildlife tr

apping surveys.  When found at approximately 0550 the animal appeared lethargic.  It was handled to determine sex and condition.  The animal was alive but not reactive enough to release.  It was placed inside a cotton bag and then inside a shirt pocket.  The animal travelled this way until the completion of checking all traps in the Bobbin Head section of the survey.  The animal was then re assessed regularly over the next 3 hours of the survey.  The animal died at approx 0845.

GROSS FINDINGS

External examination:  Moderate numbers of ticks and mites are scattered throughout the pelage.  A large tick is adherent to the skin of the right axilla.  Numerous small ticks are adherent to the pinnae.

Hydration: good

Muscle mass: good

Fat deposits: good

Internal examination: The tissues are well preserved. The small intestine is distended with gas and contains black, viscous material. The stomach is devoid of ingesta. The testes are very large.

HISTOLOGICAL FINDINGS

The tissues are well preserved, with exception of the lower small intestines, which are markedly autolytic.

Lesions are not evident in the following tissues: brain, spleen, pancreas (B), liver, kidney, autolytic intestine (C)

The following observations are notable:

Skeletal muscle (A): Scattered myocytes contain large intracellular elongate oval, cytoplasmic protozoal cysts. These structures have a very thin, refractile wall, and contain very large numbers of small internal zoites.

Testis (A):  Spermatogenesis is only evident within a small proportion of spermatic cords.  Scattered cords contain luminal cells with very large, basophilic nuclei.  The epididymis contains a large granuloma composed of central spermatozoa and surrounded by a rim of macrophages and multinucleate giant cells.  An adjacent bundle of epididymal tubules also contains spermatozoa and the interstitium contains a moderate infiltrate of polymophonuclear cells.  The remaining epidiymal tubules rarely contain spermatozoa.

Skin (A):  Multifocally, the keratin layer contains small, cellular exudate.

Myocardium (A):  Segmentally, epicardial myocytes are hypereosinophilic and have pyknotic nuclei.  Similar clusters of myocytes are evident throughout the myocardium.

Prostate gland (A): Segmentally, a group of prostatic glands contain sloughed epithelial cells that have large, smudgy, basophilic intranuclear inclusion bodies. Focally, a gland is lined with epithelial cells that have very large nuclei with peripheralised chromatin and very large intranuclear basophilic inclusion bodies. In the same section, a single gland is distended with a large number of luminal coccidial oocysts and gametocytes. The mucosa of this gland is a single layer of squamous epithelium.

Lung (B):  The pulmonary parenchyma is mildly congested.  The interstitium contains moderate numbers of polymorphonuclear cells.

Small intestine (B):  The intestinal lumen contains a longitudinal section of a nematode parasite.

Stomach (C):  The squamous and glandular stomachs contain luminal nematode parasites.  The lumen also contains abundant acid haematin.  Multifocal segments of the mucosa exhibit acute coagulation necrosis.  Haemorrhage is evident at the margins of one of these foci.

DIAGNOSIS

Ectoparasitism – ticks, mites

Gastric ulceration and meleana – multifocal, acute

Cardiomyopathy – mild, acute

Muscle protozoa – presumed Sarcocystis or Neospora sp.

Testicular and prostatic intranuclear inclusions – basophilic, large – presumed herpes virus

Prostatic coccidia

Epididymal spermatocoel

Intestinal nematodiasis

Gastric nematodiasis

COMMENTS

The antechinus died shortly after being recovered in poor condition from being trapped overnight in an Elliot trap.  There was no evidence of traumatic injury upon gross post mortem examination of the animal.  Evidence of digested blood was found in the intestinal cavity.  This is most likely evidence of gastrointestinal ulceration, which is a common occurrence associated with shock, circulatory collapse and resulting ischaemia in antechinus.  Breeding male antechinus have been shown to have high concentrations of circulating corticosteroids, which has been associated with gastric ulceration in males that die just after the breeding season.

Histopathology was conducted and confirmed the presence of acute myocardial damage, which can be another common sign of ischaemia associated with shock/circulatory collapse.

The animal had a wide variety of underlying parasitic infections, and viral infection in its prostate gland and testis.  Although largely incidental findings, some of these parasites will be further studied and identified.

The inclusions in the prostate and testicle are consistent with herpesvirus infection, which has been previously described in breeding male antechinus.  There is some debate as the potential effects of this virus on the immune system of the host.  Historically this virus was thought to be a cytomegalovirus, but more recently, it has been described by Wilks et al as a gamma herpes virus.

It was interesting to note that the animal trapping was timed to occur before the antechinus breeding season, and this animal had very little active sperm production, yet it had many mature spermatozoa trapped within a blocked tubule in the epididymis.  It seems likely that this male had previously bred and avoided post-breeding mortality.  Perhaps the age of this animal may have predisposed it to be more sensitive to subsequent stressful events.

The finding of reproducing coccidia within the prostate gland of this animal is very interesting and rare.  The identification of this organism and its relationship to the coccidial parasite cysts (thought to be Neospora or Sarcocystis sp) will be further studied through a PhD student at the University of Sydney.