Sheep-Associated Malignant Catarrhal Fever: Role of Latent Virus and Macrophages in Vasculitis

Malignant catarrhal fever in a goat: manifestation of virus-induced erythema multiforme

Malignant catarrhal fever (MCF), caused by ovine herpesvirus 2 (OvHV2; Orthoherpesviridae, Macavirus ovinegamma2), has sheep as natural hosts. OvHV2 is an important macavirus globally that induces fatal disease in dead-end hosts. Goats, which can be infected subclinically with OvHV2, rarely develop MCF. A 28-wk-old female goat was presented with fever and multifocal crusty skin lesions. Histologic examination of a skin biopsy suggested erythema multiforme (EM), with pyoderma and dermal vasculitis. The doe was euthanized and subjected to postmortem and histologic examination. MCF was suspected and PCR assays for macaviruses were performed, followed by immunohistochemistry (IHC) for OvHV2 latency-associated nuclear antigen (oLANA), RNA in situ hybridization for Ov2.5 mRNA, and IHC to characterize infiltrating leukocytes. The main postmortem finding was severe multifocal ulcerative dermatitis with macrophage- and T cell-mediated arteritis. The latter was also detected in kidney, spleen, heart, and intestinal wall. The PCR assay detected high loads of OvHV2 in tissues. OvHV2 oLANA and Ov2.5 mRNA were expressed within the lesions in leukocytes, endothelial cells, fibroblasts, and/or keratinocytes. Our case confirms that MCF can initially manifest clinically as a skin disease in goats and as EM with confirmed viral etiology.

Ivermectin inhibits replication of the malignant catarrhal fever virus alcelaphine herpesvirus 1

Malignant catarrhal fever is a lymphoproliferative disease of cattle and other ungulates that is caused by genetically and antigenically related gamma herpesviruses of the genus Macavirus. Infection of the natural host species is efficient and asymptomatic but spread to susceptible hosts is often fatal with clinical signs including fever, depression, nasal and ocular discharge. There is no recognised treatment for MCF but a vaccine for one MCF virus, alcelaphine herpesvirus 1 (AlHV-1), has been described. In this paper we describe the inhibition of AlHV-1 replication and propagation by the anthelminthic drug ivermectin. Concentrations of 10 μM or greater led to significant reductions in both copy number and viable titre of virus tested in culture medium, with little replication detected at over 20 μM ivermectin. In the absence of alternative treatments, further testing of ivermectin as a candidate antiviral treatment for MCF may therefore be justified.

Granulomatous mural folliculitis in 16 domestic goats: Infection with malignant catarrhal fever viruses and colocalization with ovine herpesvirus-2 using in situ hybridization

Granulomatous mural folliculitis (GMF) is an uncommon reaction pattern occasionally observed in nonadapted ruminant hosts infected with malignant catarrhal fever viruses. This report characterizes GMF and concurrent cutaneous lesions in 16 goats with crusting dermatitis using histochemistry including hematoxylin and eosin, periodic acid-Schiff, and Grocott's methenamine silver, and immunohistochemistry for CD3, CD20, ionized calcium binding adaptor molecule 1, and cytokeratin AE1/3. Infiltrates in all 16 GMF cases consisted of macrophages and fewer T lymphocytes, and variably included eosinophils, multinucleated histiocytic giant cells, and/or neutrophils. Formalin-fixed paraffin-embedded skin and fresh skin samples from caprine GMF cases were tested using pan-herpesvirus nested conventional polymerase chain reaction (PCR) and partial sequencing, ovine herpesvirus-2 (OvHV-2) real-time PCR, and OvHV-2 colorimetric in situ hybridization (ISH). Five of 16 goats with GMF (31%) were PCR positive for malignant catarrhal fever viruses, including caprine herpesvirus 3 in 1 goat and OvHV-2 in 4 goats. Three goats also had positive intranuclear OvHV-2 hybridization signal in follicular keratinocytes, among other cell types, localized to areas of GMF. Herpesviruses were not detected in the formalin-fixed paraffin-embedded skin of 9 goats without GMF. This case series describes relatively frequent detections of malignant catarrhal fever viruses in the skin of goats with GMF, including the first report of caprine herpesvirus 3, and localizes OvHV-2 infected follicular keratinocytes within areas of GMF.

Evidence for a Novel Gammaherpesvirus as the Putative Agent of Malignant Catarrhal Fever Disease in Roan Antelopes (Hippotragus equinus)

Upon the sudden death of two captive roan antelopes (Hippotragus equinus) that had suffered from clinical signs reminiscent of malignant catarrhal fever (MCF) in a German zoo, next generation sequencing of organ samples provided evidence of the presence of a novel gammaherpesvirus species. It shares 82.40% nucleotide identity with its so far closest relative Alcelaphine herpesvirus 1 (AlHV-1) at the polymerase gene level. The main histopathological finding consisted of lympho-histiocytic vasculitis of the pituitary rete mirabile. The MCF-like clinical presentation and pathology, combined with the detection of a nucleotide sequence related to that of AlHV-1, indicates a spillover event of a novel member of the genus Macavirus of the Gammaherpesvirinae, probably from a contact species within the zoo. We propose the name Alcelaphine herpesvirus 3 (AlHV-3) for this newly identified virus.

Histophilus somni disease conditions with simultaneous infections by ovine gammaherpesvirus 2 in cattle herds from Southern Brazil

This report investigated the cause of cattle mortality in two farms in Southern Brazil. The tissues of one animal from each farm (animals #1 and #2) respectively were used in pathological and molecular investigations to determine the possible cause of death. The principal pathological findings observed in animal #1 were pulmonary, myocardial, and encephalitic hemorrhages with vasculitis, and lymphoplasmacytic interstitial pneumonia with proliferative vascular lesions (PVL). The main pathological findings observed in animal #2 were purulent bronchopneumonia, hemorrhagic myocarditis, and lymphoplasmacytic interstitial pneumonia with PVL. An immunohistochemical assay detected intralesional antigens of a malignant catarrhal fever virus (MCFV) from multiple tissues of animal #2 while PCR confirmed that the MCFV amplified was ovine gammaherpesvirus 2 (OvGHV2), genus Macavirus, subfamily Gammaherpesvirinae; OvGHV2 was also amplified from multiple tissues of animal #1. Furthermore, PCR assays amplified Histophilus somni DNA from multiple fragments of both animals. However, the nucleic acids of Mannheimia haemolytica, Pasteurella multocida, Mycoplasma bovis, bovine respiratory syncytial virus, bovine alphaherpesvirus virus 1 and 5, bovine coronavirus, and bovine parainfluenza virus 3 were not amplified from any of the tissues analyzed, suggesting that these pathogens did not participate in the development of the lesions herein described. These findings demonstrated that both animals were concomitantly infected by H. somni and OvGHV2 and developed the septicemic and encephalitic manifestations of H. somni. Furthermore, the interstitial pneumonia observed in cow #2 was more likely associated with infection by OvGHV2.

Systemic proliferative arteriopathy and hypophysitis in a cow with chronic ovine herpesvirus 2-induced malignant catarrhal fever

Malignant catarrhal fever (MCF) is a severe, systemic, lymphoproliferative disease affecting domestic ruminants, caused by a group of MCF viruses in the genus Macavirus. Infection of cattle and bison with ovine herpesvirus 2 (OvHV2) is economically significant in North America. Sheep are the reservoir host of the virus, and only rarely manifest disease. Cattle and bison, however, frequently have lymphoproliferation, mucosal ulceration, and systemic vasculitis. OvHV2-induced MCF in cattle and bison is often fatal, with clinical recovery reported only rarely. Chronic cases are uncommon, but vascular changes of variable severity and ocular lesions have been described. Here we present a case of chronic MCF in a cow with proliferative arteriopathy, systemic vasculitis, and OvHV2-associated hypophysitis. We demonstrated OvHV2 nucleic acid in affected tissues with in situ hybridization.

Neuroinvasion and Neurotropism by SARS-CoV-2 Variants in the K18-hACE2 Mouse

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) not only affects the respiratory tract but also causes neurological symptoms such as loss of smell and taste, headache, fatigue or severe cerebrovascular complications. Using transgenic mice expressing human angiotensin-converting enzyme 2 (hACE2), we investigated the spatiotemporal distribution and pathomorphological features in the CNS following intranasal infection with SARS-CoV-2 variants, as well as after prior influenza A virus infection. Apart from Omicron, we found all variants to frequently spread to and within the CNS. Infection was restricted to neurons and appeared to spread from the olfactory bulb mainly in basally oriented regions in the brain and into the spinal cord, independent of ACE2 expression and without evidence of neuronal cell death, axonal damage or demyelination. However, microglial activation, microgliosis and a mild macrophage and T cell dominated inflammatory response was consistently observed, accompanied by apoptotic death of endothelial, microglial and immune cells, without their apparent infection. Microgliosis and immune cell apoptosis indicate a potential role of microglia for pathogenesis and viral effect in COVID-19 and the possible impairment of neurological functions, especially in long COVID. These data may also be informative for the selection of therapeutic candidates and broadly support the investigation of agents with adequate penetration into relevant regions of the CNS.

First Report of TTSuV1 in Domestic Swiss Pigs

Serum prevalence of Torque teno sus viruses (TTSuV1 and k2; family Anelloviridae) is known to be high in the porcine population worldwide but pathogenesis and associated pathomorphological lesions remain to be elucidated. In this study, quantitative real-time PCR for detection of TTSuV1 was performed in 101 porcine samples of brain tissue, with animals showing inflammatory lesions or no histological changes. Additionally, a pathomorphological and immunohistochemical characterization of possible lesions was carried out. Selected cases were screened by TTSuV1 in situ hybridization. Furthermore, TTSuV1 quantitative real-time PCR in splenic and pulmonary tissue and in situ hybridization (ISH) in spleen, lungs, mesenteric lymph node, heart, kidney, and liver were performed in 22 animals. TTSuV1 was detected by PCR not only in spleen and lung but also in brain tissue (71.3%); however, in general, spleen and lung tissue displayed lower Ct values than the brain. Positive TTSuV1 results were frequently associated with the morphological diagnosis of non-suppurative encephalitis. Single TTSuV1-positive lymphocytes were detected by ISH in the brain but also in lungs, spleen, mesenteric lymph node and in two cases of non-suppurative myocarditis. A pathogenetic role of a TTSuV1 infection as a co-factor for non-suppurative encephalitides cannot be ruled out.

Ovine gammaherpesvirus-2 infection associated with chronic interstitial pneumonia in a sheep

Sheep Associated-Malignant Catarrhal Fever (SA-MCF) is severe, frequently lethal, lymphoproliferative disease predominantly of ruminants, that is caused by ovine gammaherpesvirus-2 (OvHV-2), a member of the MCF virus (MCFV) complex. However, SA-MCF in sheep is a rare entity with few demonstrations of natural diseases worldwide. This report documents the clinical, radiographical, pathological, immunohistochemical, and molecular findings of SA-MCF in a sheep. A 4-year-old, female, mixed-breed sheep with progressive emaciation for at least one month was humanely euthanized due to poor prognosis. Clinically, the animal had tachypnea, ruminal hypomotility, productive coughing with bilateral muffling sounds during pulmonary auscultation. Radiographical evaluation revealed alveolar opacity of the cranioventral pulmonary region. Grossly, there were distinct rib impressions on the pleural surface of the lungs, suggestive of interstitial pneumonia. Histopathologic evaluation of the lungs revealed several disease patterns including 1) chronic interstitial pneumonia with vasculitis and proliferating vascular lesions, and thrombosis; 2) pulmonary abscesses associated with embolic dissemination of Corynebacterium pseudotuberculosis from superficial lymph node due to caseous lymphadenitis, CLA; 3) granulomatous pneumonia associated with pulmonary nematodes; and 4) chronic pleuritis, probably due to caseous lymphadenitis. Additional significant histologic findings included widespread lymphocytic vasculitis and proliferating vascular lesions in multiple tissues, atrophic enteritis, segmental degeneration of myocardial fibers with lymphocytic pericarditis, lymphocytic interstitial nephritis, and non-suppurative encephalitis. An immunohistochemistry (IHC) assay, based on the monoclonal antibody 15A (MAb-15A), that is specific to all MCFV known to cause MCF, revealed positive, intracytoplasmic, intralesional immunoreactivity, predominantly within bronchial and bronchiolar epithelial cells of the lungs and cryptal epithelial cells of the small intestine, followed by the renal tubular epithelium, cardiomyocytes, and with patchy immunolabelling within neurons of the cerebral cortex. Molecular testing done to detect a wide range of bacterial and viral agents of ruminant diseases, only amplified OvHV-2 DNA from fresh tissue fragments of the lungs, kidney, liver, spleen, and cerebrum. Direct sequencing confirmed that the PCR amplicon derived from the pulmonary fragments had 99.2-99.7% nucleotide sequence identity with OvHV-2 reference strains and strains of OvHV-2 from Brazil. The clinical, radiographical, gross, histopathologic, IHC, and molecular findings in the lungs are consistent with chronic interstitial pneumonia associated with infection by OvHV-2. Furthermore, the non-detection of other viral agents associated with pulmonary diseases in ruminants suggest that OvHV-2 was directly associated with the development of chronic pneumonia in this sheep. Additionally, the dental alterations, CLA, and the pulmonary nematode may have contributed towards the reduced immunological statue of the animal and facilitated the occurrence of SA-MCF. These findings may indicate that OvHV-2 may be a major participant in the pathogenesis of pulmonary disease of sheep under special conditions. Moreover, the proliferating vascular lesions identified in multiple tissues are additional evidence of chronic manifestations of OvHV-2 infections as described in chronic SA-MCF of cattle, while the widespread vasculitis is consistent with SA-MCF. Additionally, the IHC findings using the MAb-15A confirmed that this diagnostic approach is efficient to identify intralesional antigens of OvHV-2.