Prevalence of the AMHR2 mutation in Miniature Schnauzers and genetic investigation of a Belgian Malinois with persistent Müllerian duct syndrome.

Persistent Müllerian duct syndrome (PMDS) is a sex-limited disorder in which males develop portions of the female reproductive tract. Important consequences of PMDS are cryptorchidism and its sequelae of infertility and increased risk of testicular cancer. Anti-Müllerian hormone (AMH) and its receptor (AMHR2) induce the regression of the Müllerian ducts in male embryos. In Miniature Schnauzer dogs, the genetic basis has been identified as an autosomal recessive nonsense mutation in AMHR2, but the allele frequency of the mutation is unknown. Thus, the primary objective of this study was to estimate the prevalence of the AMHR2 mutation in North American Miniature Schnauzers, in order to ascertain the value of genetic testing in this breed. An additional objective was to determine whether mutations in AMH or AMHR2 were responsible for PMDS in a Belgian Malinois; this would aid development of a genetic test for the Belgian Malinois breed. Genomic DNA from 216 Miniature Schnauzers (including one known PMDS case) was genotyped for the AMHR2 mutation, and DNA from a single PMDS-affected Belgian Malinois was sequenced for all coding exons of AMH and AMHR2. The Miniature Schnauzer cohort had an AMHR2 mutation allele frequency of 0.16 and a carrier genotypic frequency of 0.27. The genetic basis for PMDS in the Belgian Malinois was not determined, as no coding or splicing mutations were identified in either AMH or AMHR2. These findings support a benefit to AMHR2 mutation testing Miniature Schnauzers used for breeding or with cryptorchidism.

Distribution of viral antigen in tissues of new-born lambs infected with Rift Valley fever virus.

The distribution of Rift Valley fever (RVF) viral antigen was studied by immunohistochemistry in the liver, spleen, prescapular lymph node, lungs and kidneys ot eight experimentally infected new-born lambs and in four new-born lambs that died of RVF during the 1974-75 RVF epidemic. The eight experimentally infected lambs were euthanazed at 6, 12, 18, 24, 30, 33, 48 and 51 h post-infection (p.i.), respectively. Immunohistochemical staining utilized polyclonal hyperimmune mouse ascites fluid to RVF virus and peroxidase-diaminobenzidine was substrate. Virus antigen was most prominent in the liver and was detected as early as 18 h p.i. in the cytoplasm of hepatocytes that were sparsely scattered throughout the lobules. At 24-33 h p.i. antigen was also present in or adjacent to small foci of hepatocellular necrosis. At 48-51 h p.i. and in one of the field cases, positive staining was widespread and most consistently present in the cytoplasm of large numbers of degenerated or necrotic hepatocytes and in a new acidophilic bodies. Immunohistochemical staining was rarely observed in hepatocyte nuclei. Almost diffuse histochemical staining was observed in disintegrated cells and in the cytoplasm of necrotic hepatocytes throughout the liver in the other three field cases with pannecrosis; only the primary foci necrosis and a narrow periportal rim of intact hepatocytes did not stain. No staining was observed in bile duct epithelium, endothelial and Kupffer cells in the initial stages of Infection, supporting the contention that hepatocytes constitute the primary site of RVF virus replication in new-born lambs. Few cells stained positively in the spleen, prescapular lymph node, lungs and kidneys.

The diagnosis of Wesselsbron disease in a new-born lamb by immunohistochemical staining of viral antigen.

Wesselsbron disease (WSL) was diagnosed in a 2-d-old lamb on a farm in the north-eastern Free State Province where a few abortions and neonatal deaths occurred in sheep in April 1994. The liver of the lamb was slightly swollen and orange-brown and, microscopically, it revealed single or small groups of necrotic hepatocytes that were randomly scattered throughout the lobules. Other histopathologic hepatic lesions included the presence of acidophilic bodies, intranuclear inclusion bodies in a few hepatocytes, neutrophils in the parenchyma, mild Kupffer-cell and bile-ductular proliferation and infiltration of mixed inflammatory cells in the portal tracts. Immunohistochemical staining of sections of formalin-fixed specimens of the liver with polyclonal antibody against WSL virus revealed positive staining in acidophilic bodies, cytoplasmic fragments of necrotic liver cells, the cytoplasm of degenerated hepatocytes and, rarely, in intranuclear inclusions. Positive staining was also obtained in liver sections from two newborn lambs experimentally infected with WSL virus. The results of this investigation showed that the immunohistochemical staining of sections of formalin-fixed liver can be used to confirm the diagnosis of WSL in new-born lambs.

Application of immunoperoxidase techniques to formalin-fixed brain tissue for the diagnosis of rabies in southern Africa.

Two immunoperoxidase techniques, viz. avidin-biotin complex (ABC) and peroxidase-anti-peroxidase (PAP) procedures, were applied to paraffin-wax-embedded brain-tissue sections, from brains which had been fixed in 10% formalin, to demonstrate the presence of rabies-virus antigen by light microscopy. These techniques positively identified both "viverrid" and "canid" rabies-virus antigen in tissues sections of species commonly infected with rabies virus in southern Africa, viz. the domestic dog (Canis familiaris), yellow mongoose (Cynictus penicillata), black-backed jackal (Canis mesomelas), bat-eared fox (Otocyon megalotus), cattle (Bos taurus), sheep (Ovis aries) and humans. With both of these techniques rabies-virus antigen stained as sharply demarcated, brown precipitates within the cytoplasm of neurons. The virtual absence of background staining enabled identification of fine granules of viral antigen, often referred to as "virus dust", within axons, dendrites and cytoplasm of the nerve cell body. Staining with the ABC procedure clearer, more deeply-coloured precipitates than the PAP method.