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. 


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.
VirusDisease name Gross findings HistologySpeciesTransmission
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 hypoplasiaRuminants: sheep, goats, cattle, bisonsArbovirus: 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 formationNon-suppurative encephalo-myelitis, neuronal loss in the spinal cord, muscular dysplasiaHerbivores: cattle, horses, donkeys, sheep, goats, camels, buffaloes, pigsArbovirus: 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 hypoplasiaperivascular non-suppurative meningeal infiltration, CNS malacia, hypomyelinogenesis, retinal degeneration, optic neuritis, myocarditisCattle, 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, runtingNecrotizing meningoencephalitis, interstitial pneumonia, mono-nuclear cells in kidney and liverSheep, 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, kyphoscoliosisDys- and hypomyelinationSheep, goats, pigs, cattleOral, conjuctival, intranasal, genital, semen
Cache valley virus, syn. Bunyamwera virus(5,20)
Orthobunyavirus, Bunyaviridae
Arthrogryposis, hydrocephalus, hydranencaphaly, microcephaly, vertebral malformations, cerebellar hypoplasia, micromelia, porencephalyNecrosis and loss of neuropil and motor neurons, myositis, poorly developed myocytesSheep, deer, caribou, pigs, horses, cattle, raccoons, foxes, manArbovirus: Culicoides sp.,Culiseta sp., Anopheles sp.
Chuzan virus, syn. Palyamvirus(20)
Orbivirus, Reoviridae
Hydranencephaly, cerebellar hypoplasia, hydrocephalus, microcephaly CattleArbovirus: Culicoides oxystoma
Classical swine fever virus(20)
Pestivirus, Flaviviridae
Hog choleraMummification, 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 degenerationPigs, cattle, sheep, goatsExcretions, ingestion
Rift valley fever virus(20,23)
Phlebovirus, Bunyaviridae
Intra-uterine fetal deathHepatic necrosis, acidophilic intranuclear inclusions, cholestasis, degeneration of lympho-cytes, heart muscle and renal tubulesSheep, cattle, goats, manArbovirus: 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 ductsSheep, cattle, manArbovirus
Aino virus, syn. Shuni virus(3,21,25)
Orthobunyavirus, Bunyaviridae
Arthrogryposis-hydranencephaly syndrome (CAHS)Hydranencephaly, arthrogryposis, cerebellar hypoplasiaNecrotizing encephalopathy, perivascular cuffing with lymphoid cells, neuronal mineralizationCattle, sheepArbovirus: 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. 


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Click the slide to view.

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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