Signalment:  

A newborn, female lamb (Ovis aries) of unknown breed.The sheep was born alive and died perinatally with a body weight of 5.3 kg. The animal originated from an area in the southeast of North Rhine-Westfalia, district of Siegen in Germany, which is approximately 50 km apart from the town of Schmallenberg.

Gross Description:  

Gross pathological findings consisted of torticollis, cerebellar hypoplasia, and hydranencephaly

Histopathologic Description:

Frontal cerebral cortex: The cerebrum shows a bilateral focally extensive reduction of the thickness of the dorsal cortex (0.5 to 1 mm) associated with cystic cavities (pores). Within the pores multiple fine strands of residual pre-existing nervous tissue are present. The affected cerebral cortex displays a severe, diffuse loss of the gray and white matter with widespread destruction of tissue architecture and accumulation of cellular debris (karyorrhectic, karyolytic and pyknotic cells) consistent with liquefactive necrosis. In addition, a low amount of irregular shaped, acellular, dark basophilic, coarsely granular material (mineralization) up to 30 μm in diameter is found scattered throughout the cortex. A moderate diffuse neuronal loss with neuronal degeneration characterized by hypereosinophilic, chromatolytic, shrunken and pyknotic neurons is found. Furthermore, few round to oval cells with a diameter up to 25 μm, eccentric nuclei and foamy, eosinophilic cytoplasm (Gitter cells) as well as plump astrocytes containing a homogenous, eosinophilic cytoplasm (gemistocytes) are present throughout the pores. The cerebral cortex shows a diffuse and moderate capillary proliferation with prominent vessels associated with endothelial swelling (neovascularisation). Both lateral ventricles are moderately distended (up to 0.7 mm in diameter). Predominantly the gray and white matter of the ventral parts of the cerebral cortex display a moderate to severe, multifocal perivascular cuffing (up to 20 layers) and diffuse meningeal infiltration of lymphocytes and macrophages. Diffusely slight parenchymatous infiltrates are dominated by lymphocytes. In addition, rod-shaped microglial cells/macrophages (microgliosis) and astrocytes (astrogliosis) are present. 

Morphologic Diagnosis:  

Frontal cerebral cortex, bilateral, focally extensive liquefactive necrosis, severe, subacute to chronic, with cystic cavities, and meningoencephalitis, lympho-histiocytic, multifocal, subacute, moderate to severe.

Lab Results:  

Central nervous system and blood samples were positive for Schmallenberg virus-specific genome fragments RTqPCR. 

Condition:  

Schmallenberg virus

Contributor Comment:  

Since autumn 2011, a new emerging arthropod-borne, negative stranded ssRNA Orthobunyavirus, termed Schmallenberg virus (SBV), was detected in Europe.(11) Virus prevalence has been reported in Germany, The Netherlands, France, Belgium, Luxembourg, United Kingdom, Italy, and Spain.(7) SBV had significant economic relevance due to reduced milk yield, fever, and diarrhea in pregnant dairy cows and particularly due to abortions, and malformations of newborn ruminants.(11) Clinical signs in adult ruminants were usually limited up to a period of three weeks and affected animals recovered subsequently completely.(8) The virus was named after the town Schmallenberg in western Germany, because the first identification of the virus succeeded in samples of cattle housed next to this town. Similar to other Orthobunyaviruses, like Akabane virus, SBV causes malformations in newborn ruminants due to a prenatal infection. Macroscopically, malformations comprise arthrogryposis, vertebral malformations, brachygnathia inferior as well as various central nervous system (CNS) malformations like hydranencephaly, porencephaly, internal hydrocephalus, cerebellar hypoplasia and micromyelia in lambs, goat kids and calves.(10) Until now, it is not known how exactly SBV arrived in Germany, but parallels were made to the epidemiology of Blue tongue virus, which emerged first in Europe in 2006 and is also transmitted via arthropods.(17) Possible routes of SBV entry to Europe are insects and/or animals in aircrafts or import of cut flowers from Africa.(17)

Based on metagenomic analysis,(11) SBV belongs to a group of teratogenic viruses causing arthrogryposis and hydranencephaly (AG/HE). These malformations in cattle caused by Akabane virus represent an entity called enzootic bovine arthrogryposis and hydranencephaly.(20)

Until now the pathogenesis of SBV infection is not fully understood. Due to a genetic relationship to other viruses of the genus Orthobunyavirus, a similar pathogenesis is suggested.(12) Furthermore, the SBV-induced pathology cannot be differentiated from infections with Akabane virus(12) which requires an identification at the molecular level with PCR.(11) Appropriate samples for the detection of viral nucleotides by means of this technique are external placental fluid, umbilical cord, cerebrum, and spinal cord.(2) Placental fluid and umbilical cord samples can be taken easily without necropsy. The central nervous system is accessible in animals submitted for necropsy without placental fluid and only umbilical cord remnants.(2) Spleen, cartilage, placental fluid from the stomach, and meconium rarely revealed a positive PCR result in SBV-infected animals and therefore these samples should be avoided for virus detection.(2) In addition, placenta and placental fluid of SBV-infected animals contain huge amounts of virus.(2) So far the host range of SBV seems to be restricted to ruminants and there is no evidence of a zoonotic risk.(6)

A recent study compared genomic RNA of SBV with Sathuperi and Shamonda viruses indicating that all viruses belong the genus Orthobunyavirus and that SBV originates from a re-assortment of Sathuperi and Shamonda virus.(26)

In general, climate change is suggested to be the most important factor for the occurrence of arthropod-borne virus-infections in Europe.(9) SBV is supposed to be transmitted by arthropods, but the high numbers of initial SBV infections in Europe suggest additional routes of transmission, e.g. direct contact, fecal-oral route or aerosols.(1)

Interestingly, in the present case the lambs CNS showed liquefactive necrosis with porencephaly and additional non-suppurative inflammation. Studies with the closely related Akabane virus showed that the virus crosses the placenta after viremia and replicates in fetal cells of the central nervous system. The virus prefers rapidly dividing cells and causes damage to neurons.(24) Depending on the time point of infection, CNS pathology varies. According to Akabane virus infection, it is suggested that transplacental SBV infection at early stages of gestation causes severe brain lesions, like hydranencephaly due to a widespread loss of neuronal tissue. The severity of brain damage is less extensive, if the infection occurs to a later time point of gestation. Infection during the 2nd trimester may result in a more focal necrosis of the CNS characterized by porencephaly. This porencephaly can be associated with a meningoencephalitis.(20) Assuming that Akabane virus and SBV have a similar pathogenesis, an infection during the 2nd trimester is suggested in the present case. Our study revealed that only 20% (12 out of 58 animals) of all RTqPCR positive tested CNS samples of ruminants (lambs, goat kids and calves) showed meningoencephalitis with or without CNS malformations.(10) Infiltration of lymphocytes and macrophages showed a perivascular pattern. Furthermore, gitter cell formation and neuronal necrosis were present. For further characterization of the lesions several special stains were applied including von Kossa-�s stain, Luxol fast-blue stain, and Bielschowsky-�s silver impregnation. Intralesional amorphous basophilic material stained positive with a von Kossa stain indicating intralesional mineralization, which was found multifocally in the thin cortical areas of the pore. Demyelination was shown as reduced staining intensity in the cortex containing pores. Bielschowsky-�s silver impregnation was used to investigate the extent of axonal alterations. The amount of positive axons was reduced. 

The following table lists possible etiological differentials of SBV infection. The described histopathological lesions are not characteristic for a particular virus. The etiology has to be proven with other methods, e.g. molecular techniques, like PCR. Further epidemiological information as well as the geographical area (e.g. Asia, Europe, USA) of occurrence have to be considered. The table summarizes information of naturally infected animals; results of experimentally infected animals were not included.

Table 1: Overview on virus infections, their pathology in offspring after natural transmission, susceptible species and the transmission mode representing possible etiological differentials of Schmallenberg virus infection.

Virus	Disease name	Gross findings	Histology	Species	Transmission
Schmallenberg virus(4,10,11)Orthobunyavirus, Bunyaviridae		Arthrogryposis, vertebral malformations, brachygnathia inferior, hydran- and porencephaly, internal hydrocephalus, cerebellar hypoplasia, micromyelia	Lymphohistiocytic meningoen-cephalomyelitis, CNS malacia, gliosis, muscular hypoplasia	Ruminants: sheep, goats, cattle, bisons	Arbovirus: mosquitos and midges: e. g.  Culex obsoletus, Culex dewulfi
Akabane virus(3,13,15,16,18,22) Orthobunyavirus, Bunyaviridae	Enzootic bovine arthrogryposis and hydranencephaly; congenital arthrogryposis-hydranencephaly syndrome (CAHS)	Arthrogryposis, vertebral malformations, hydranencephaly, CNS cyst formation	Non-suppurative encephalo-myelitis, neuronal loss in the spinal cord, muscular dysplasia	Herbivores: cattle, horses, donkeys, sheep, goats, camels, buffaloes, pigs	Arbovirus: mosquitos and midges, eg. Culex sp., Aedes sp., Culicoides imicola
Bovine virus diarrhea virus(20) Pestivirus, Flaviviridae		Cerebellar hypoplasia, mummification, runting, microencephaly, hydranencephaly, hydrocephalus, microphthalmia, cataract, brachygnathism, thymic aplasia, hypotrichosis, alopecia, pulmonary hypoplasia	perivascular non-suppurative meningeal infiltration, CNS malacia, hypomyelinogenesis, retinal degeneration, optic neuritis, myocarditis	Cattle, sheep, goat, pig	Excretions, inhalation, ingestion, semen, contaminated embryo transfer fluid
Blue tongue virus(19,20) Orbivirus, Reoviridae		Porencephaly, hydranencephaly, hydrocephalus, subcortical cysts, cerebellar dysgenesis, runting	Necrotizing meningoencephalitis, interstitial pneumonia, mono-nuclear cells in kidney and liver	Sheep, wild ruminants, camelids, cattle, zoo carnivores(14)	Arbovirus: Culicoides sp.
Border disease virus(20) Pestivirus, Flaviviridae	Border disease Condition: hairy shaker	Embryonic death, mummification, fleece abnomalities, runting, cerebellar hypo- and dysplasia, micro-, por- and hydranencephaly, leukoencephalomalacia, micro-myelia, starvation, cardiac abnormalities, rarely: arthrogryposis, kyphoscoliosis	Dys- and hypomyelination	Sheep, goats, pigs, cattle	Oral, conjuctival, intranasal, genital, semen
Cache valley virus, syn. Bunyamwera virus(5,20) Orthobunyavirus, Bunyaviridae		Arthrogryposis, hydrocephalus, hydranencaphaly, microcephaly, vertebral malformations, cerebellar hypoplasia, micromelia, porencephaly	Necrosis and loss of neuropil and motor neurons, myositis, poorly developed myocytes	Sheep, deer, caribou, pigs, horses, cattle, raccoons, foxes, man	Arbovirus: Culicoides sp.,Culiseta sp., Anopheles sp.
Chuzan virus, syn. Palyamvirus(20) Orbivirus, Reoviridae		Hydranencephaly, cerebellar hypoplasia, hydrocephalus, microcephaly		Cattle	Arbovirus: Culicoides oxystoma
Classical swine fever virus(20) Pestivirus, Flaviviridae	Hog cholera	Mummification, runting, stillbirth, pulmonary hypoplasia, pulmonary artery malformation, micrognathia, arthrogryposis, cerebellar hypoplasia, microcephaly, defective myelination	Necrotizing vasculitis in CNS, intestine, skin, lymphoid depletion, endothelial degeneration, valvular fibrosis, portal fibrosis (liver), interstitial pneumonia, neuronal degeneration	Pigs, cattle, sheep, goats	Excretions, ingestion
Rift valley fever virus(20,23) Phlebovirus, Bunyaviridae		Intra-uterine fetal death	Hepatic necrosis, acidophilic intranuclear inclusions, cholestasis, degeneration of lympho-cytes, heart muscle and renal tubules	Sheep, cattle, goats, man	Arbovirus: Aedes sp., Culex sp.
Wesselsbron virus(20) Flavivirus, Flaviviridae		Mummification, hydranencephaly, arthrogryposis, hydrops amnii, porencephaly, cerebellar hypoplasia	Non-suppurative meningo-encephalomyelitis, eosinophilic, intranuclear inclusions, liver: degeneration, necrosis, Kupffer cell hyperplasia, hepatitis, hyper- and inflammation of bile ducts	Sheep, cattle, man	Arbovirus
Aino virus, syn. Shuni virus(3,21,25) Orthobunyavirus, Bunyaviridae	Arthrogryposis-hydranencephaly syndrome (CAHS)	Hydranencephaly, arthrogryposis, cerebellar hypoplasia	Necrotizing encephalopathy, perivascular cuffing with lymphoid cells, neuronal mineralization	Cattle, sheep	Arbovirus: Culicoides brevitarsis, Culex tritaeniorhynchus

JPC Diagnosis:  

Brain, cerebrum: Necrosis, liquefactive, bilateral, focally extensive, with marked gliosis, mineralization, spheroid formation, lymphohistiocytic meningoencephalitis and hydrocephalus ex vacuo. 

Conference Comment:  

The contributor provides an excellent and thorough description of this emerging Orthobunyavirus. Conference participants commented on the presence of band-like areas of microvascular proliferation (increased vascular pattern) present in the section, and speculated that these were likely due to collapse of the parenchyma, vessel dilation, and a compensatory induction of new vessel formation secondary to the release of cytokines and factors [i.e. vascular endothelial growth factor (VEGF)] associated with the inflammatory response and hypoxic conditions within these areas of parenchymal collapse. 

References:

1. Scenarios for the future spread of Schmallenberg virus. Veterinary Record. 2012;170:245-246.
2. Bilk S, Schulze C, Fischer M, Beer M, Hlinak A, Hoffmann B. Organ distribution of Schmallenberg virus RNA in malformed newborns. Veterinary Microbiology. 2012:159:236-8.
3. Brenner J, Tsuda T, Yadin H, Chai D, Stram Y, Kato T. Serological and clinical evidence of a teratogenic Simbu serogroup virus infection of cattle in Israel, 2001-2003. Vet Ital. 2004;40:119-123.
4. Conraths F, Beer M, Peters M. "Schmallenberg-Virus": Eine neue Infektionskrankheit bei Wiederk+�-�uern. Tier+�-�rztliche Umschau. 2012;5:147-150.
5. Edwards JF, Livingston CW, Chung SI, Collisson EC. Ovine arthrogryposis and central nervous system malformations associated with in utero Cache Valley virus infection: spontaneous disease. Veterinary Pathology. 1989;26:33-39.
6. Eurosurveillance editorial team: European Food Safety Authority publishes its second report on the Schmallenberg virus. Euro Surveillance. 2012;17: pii=20140.
7. Garigliany MM, Hoffmann B, Dive M, Sartelet A, Bayrou C, Cassart D, et al. Schmallenberg virus in calf born at term with porencephaly, belgium. Emerging Infectious Diseases. 2012;18:1005-1006.
8. Gibbens N. Schmallenberg virus: a novel viral disease in northern Europe. Vet Rec. 2012;170:58.
9. Gould EA, Higgs S, Buckley A, Gritsun TS. Potential arbovirus emergence and implications for the United Kingdom. Emerging Infectious Diseases. 2006;12:549-555.
10. Herder V, Wohlsein P, Peters M, Hansmann F, Baumg+�-�rtner W. Salient lesions in domestic ruminants infected with the emerging so-called Schmallenberg Virus in Germany. Veterinary Pathology. 2012;49(4):588-91.
11. Hoffmann B, Scheuch M, H+�-�per D, Jungblut R, Holsteg M, Schirrmeier H, et al. Novel orthobunyavirus in cattle, Europe, 2011. Emerging Infectious Diseases. 2012;18:469-472.
12. H+�-�per D, Wernike K, Eschbaumer M, Conraths F, Hoffmann B, Schirrmeier H, et al. "Schmallenberg-Virus" - Ein neues Virus in Europa. Deutsches Tier+�-�rzteblatt. 2012;4:500-505.
13. Huang CC, Huang TS, Deng MC, Jong MH, Lin SY. Natural infections of pigs with akabane virus. Veterinary Microbiology. 2003;94:1-11.
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17. Kupferschmidt K. Infectious disease. Scientists rush to find clues on new animal virus. Science. 2012;335:1028-1029.
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19. Maclachlan NJ, Drew CP, Darpel KE, Worwa G. The pathology and pathogenesis of bluetongue. Journal of Comparative Pathology. 2009;141:1-16.
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22. Parsonson IM, McPhee DA, Della-Porta AJ, McClure S, McCullagh P. Transmission of Akabane virus from the ewe to the early fetus (32 to 53 days). Journal of Comparative Pathology. 1988;99:215-227.
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Click the slide to view.

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3-1. Cerebrum

3-2. Cerebral cortex

3-3. Cerebral cortex

3-4. Cerebral cortex

3-5. Cerebral cortex

3-6. Cortical tissue

3-7. Cerebral cortex

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