Experimental infection of cows with newly isolated Akabane virus strain (AKAV-7) causing encephalomyelitis

Pathogenicity analysis of a Chinese Genogroup II Akabane virus strain (TJ2016) in mouse models

BACKGROUND

Akabane virus (AKAV) is divided into five genogroups (I to V), and strains of different genogroups exhibit marked differences in pathogenicity. We isolated a genogroup II AKAV strain, TJ2016, in China in 2016, but its virulence remains unknown. The pathogenic potential of other genogroup II strains isolated in China also remains uncharacterized. The objectives of this study were to determine the pathogenicity of TJ2016.

METHODS

Kunming or Balb/c mice at 7 days or 8 weeks of age were inoculated with TJ2016 by intracerebral (IC), intraperitoneal (IP), subcutaneous (SC), or intramuscular (IM) routes. Clinical signs, pathological alterations, and AKAV distributions in the inoculated mice were monitored and analyzed.

RESULTS

Virus inoculations by the IC route resulted in 75% ~ 100% mortality of the inoculated mice regardless of the mouse strains or ages. Virus inoculations by the IP route killed 75% to 100% of the suckling mice but killed no adult mice. All the mice inoculated via SC and IM routes survived until the end of the trial. AKAV was detected only in the brains of the mice that died or were euthanized before the end of the experiment. The AKAV antigens were only identifiable within neuronal cells. Brain lesions such as proliferation and infiltration of microglial cells, perivascular cuffing (PVC) of lymphocytes and macrophages, neuronal degeneration/necrosis, vascular dilatation and congestion, etc., were observed only in the mice that died or were euthanized before the end of the experiment.

CONCLUSIONS

We characterized the virulence of TJ2016 by inoculating suckling and adult mice via different routes and established experimental mouse models, which holds significant implications for vaccine/drug development and further research on viral pathogenesis.

A novel approach using IFNAR1 KO mice for assessing Akabane virus pathogenicity and vaccine efficacy

Akabane virus (AKAV) is a Simbu serogroup virus that can cause congenital abnormalities in ruminants. In 2010, an AKAV-7 strain exhibiting different characteristics and belonging to a distinctive genogroup compared to previous AKAVs was isolated in South Korea. Although this novel pathogenic AKAV-7 has been discovered, in vivo studies on AKAV-7 are currently insufficient due to limitations of using large animals and suckling mice. Therefore, the development of a novel small animal model for AKAV studies is necessary. Type I interferon receptor knock out (IFNAR1 KO) mice are widely employed as an infection model for Bunyavirales viruses. Here, we evaluated the suitability of IFNAR1 KO mice as a small animal model for AKAV infection. IFNAR1 KO mice inoculated with AKAV-7 strain by intraperitoneal (IP) and subcutaneous (SC) routes showed 100% mortality with high viral loads in organs and histopathological changes in the spleen and liver. These findings suggest that IFNAR1 KO mouse is susceptible to AKAV-7 infection and suitable for use as a uniformly lethal mouse model of AKAV-7. Furthermore, IFNAR1 KO mice vaccinated with the AKAV vaccine showed full protection against AKAV-7 challenge, suggesting that IFNAR1 KO mice might be useful as an animal model for AKAV vaccine studies.

Investigating the reassortment potential and pathogenicity of the S segment in Akabane virus using a reverse genetics system

BACKGROUND

Akabane virus (AKAV) is an arthropod-borne virus that causes congenital malformations and neuropathology in cattle and sheep. In South Korea, AKAVs are classified into two main genogroups: K0505 and AKAV-7 strains. The K0505 strain infects pregnant cattle, leading to fetal abnormalities, while the AKAV-7 strain induces encephalomyelitis in post-natal cattle. The pathogenicities of K0505 and AKAV-7 strains differ significantly; however, the specific gene in the AKAV-7 strain that drives its pathogenicity remains unidentified. In this study, changes in viral replication and pathogenicity were investigated, particularly when the S segment of AKAV-7 was mutated using a T7 RNA polymerase-based reverse genetics (RG) system.

RESULTS

The rAKAV-7ΔNSs virus, with a deletion in the NSs protein of the wild-type AKAV-7 virus (wtAKAV-7), and the rAKAV-7(S-K0505) virus, where the S segment of wtAKAV-7 was reassorted with that from the wild type K0505 strain (wtK0505), were successfully rescued. The rAKAV-7ΔNSs virus demonstrated impaired replication in Vero cells and exhibited reduced mortality and RNA viral load in the organs of suckling mice compared to the wtAKAV-7. The rAKAV-7(S-K0505) virus displayed similar growth kinetics in Vero cells and showed no significant reduction in mortality rate in suckling mice compared to wtAKAV-7.

CONCLUSIONS

These observations suggest that the S segment, especially the NS protein, is associated with the pathogenicity of AKAV-7. Also, the results imply that the L and M segments might explain the differences in pathogenicity between the AKAV-7 and K0505 strains. Moreover, our findings indicate the potential for reassortment between distinct genogroups of AKAVs.

Study of Akabane disease in an Iranian dairy herd: a re-emerging disease

Akabane virus is a teratogenic pathogen transmitted by Culicoides spp. to ruminants. The virus induces anomalies in the central nervous system in the developing fetus, resulting in arthrogryposis-hydranencephaly (A-H) syndrome. During three outbreaks of the disease (2002, 2013, and 2020), 77 calves were born in Varamin, Iran, with A-H syndrome. The presenting neurologic signs were categorized into three main groups, as common, less common, and uncommon signs. The common signs were unawareness of the surroundings, blindness, deep depression, partial failure of suckling, and unintelligent behavior. The less commonly noted signs were hyperexcitability, regurgitation, head pressing, compulsive walking, and kicking, while the uncommon signs comprised protrusion of the tongue, making sounds resembling barking, carnivore-like milk drinking, and deafness. Arthrogryposis, dome-shaped skull, kyphosis, torticollis, lordosis, scoliosis, and spina bifida were the diagnosed skeletal defects. Upon necropsy, hydranencephaly, hydrocephaly, and microencephaly were seen in the calves presenting neurologic signs, while astrocytosis, astrogliosis, focal gliosis, perivascular, perineuronal, and submeningeal edema, perivascular cuffing, non-suppurative meningitis, non-suppurative encephalitis and lymphoplasmacytic infiltration, and perivascular and parenchymal hemorrhage were seen in samples obtained from the brains. RT-PCR detected Akabane virus in the brain tissues of the affected calves. This is the first clinical study of Akabane disease in calves in Iran.

Different organ and tissue tropism between Akabane virus genogroups in a mouse model

Akabane virus (AKAV) is an etiological agent that is teratogenic to the fetus of domestic ruminants, causing a significant loss of reproduction in livestock. In East Asia, AKAV isolates form two major clusters: genogroups I and II. In recent years, genogroup I isolates have also been associated with postnatal encephalomyelitis, mainly in calves. Here, we compared the pathogenicity in mice using genogroup I Iriki and genogroup II OBE-1 strains. Only mice infected intraperitoneally with the Iriki strain died and showed marked replication in the central nervous system (CNS) and lymphoid tissues. A more elevated blood-brain barrier (BBB) permeability was found in the Iriki-infected mice in the clinical phase, indicating that the BBB might be a possible route of viral transmission from the periphery to the CNS. These findings demonstrate that the Iriki strain presents greater neurovirulence and neuroinvasiveness compared with the OBE-1 strain, determining different AKAV pathogenicity among genogroups.

Histopathological, Immunohistochemical and In-Situ Hybridization Findings in Suckling Rats Experimentally Infected With Akabane Genogroups Ⅰ and Ⅱ, Aino and Peaton Viruses

Akabane, Aino and Peaton viruses are closely related arthropod-borne viruses in the genus Orthobunyavirus of the family Peribunyaviridae that can cause congenital abnormalities in cattle, sheep and goats. East Asian Akabane virus strains are subdivided into genogroups Ⅰ and Ⅱ, and the former can also cause non-suppurative encephalomyelitis in post-natal animals. Specific detection of the infecting virus in tissues is essential for accurate diagnosis. Immunohistochemistry (IHC) has been used to identify viral antigen but cannot always detect specific viruses due to potential cross-reactivity of the primary antisera. We compared in-situ hybridization (ISH), based on the use of cocktail probe sets targeted at the RNA of each virus, with IHC for the detection of the specific viruses in tissues of suckling rats inoculated intracerebrally with Akabane (KM-1 or OBE-1 strains), Aino or Peaton viruses at 3 or 7 days of age. Most inoculated rats developed severe neurological signs and histopathological brain lesions including necrosis, spongy degeneration and non-suppurative inflammation. A rabbit polyclonal antiserum immunolabelled antigen of all three viruses within the lesions, whereas ISH specifically detected RNA of each individual virus. The distribution of viral RNA was comparable to that of viral antigens, but tended to be more widespread, especially in immature nervous tissue. Viral antigen and RNA were detected in skeletal muscle and heart of the rats infected with the KM-1 strain of Akabane virus but not with any of the other viruses. This study demonstrates the value of ISH detection of these viruses in a rat model and may prove useful for clarification of the pathogenesis of post-natal arbovirus infection.

Shuni virus-induced meningoencephalitis after experimental infection of cattle

Shuni virus (SHUV), an insect-transmitted orthobunyavirus of the Simbu serogroup within the family Peribunyaviridae, may induce severe congenital malformations when naïve ruminants are infected during gestation. Only recently, another clinical presentation in cattle, namely neurological disease after postnatal infection, was reported. To characterize the course of the disease under experimental conditions and to confirm a causal relationship between the virus and the neurological disorders observed in the field, six calves each were experimentally inoculated (subcutaneously) with two different SHUV strains from both clinical presentations, that is encephalitis and congenital malformation, respectively. Subsequently, the animals were monitored clinically, virologically and serologically for three weeks. All animals inoculated with the 'encephalitis strain' SHUV 2162/16 developed viremia for three to four consecutive days, seroconverted, and five out of six animals showed elevated body temperature for up to three days. No further clinical signs such as neurological symptoms were observed in any of these animals. However, four out of six animals developed a non-suppurative meningoencephalitis, characterized by perivascular cuffing and glial nodule formation. Moreover, SHUV genome could be visualized in brain tissues of the infected animals by in situ hybridization. In contrast to the 'encephalitis SHUV strain', in animals subcutaneously inoculated with the strain isolated from a malformed newborn (SHUV 2504/3/14), which expressed a truncated non-structural protein NSs, a major virulence factor, no viremia or seroconversion, was observed, demonstrating an expected severe replication defect of this strain in vivo. The lack of viremia further indicates that virus variants evolving in malformed foetuses may represent attenuated artefacts as has been described for closely related viruses. As the neuropathogenicity of SHUV could be demonstrated under experimental conditions, this virus should be included in differential diagnosis for encephalitis in ruminants, and cattle represent a suitable animal model to study the pathogenesis of SHUV.

Comparative evaluation of two commercial ELISA kits for detection of antibodies against Akabane virus in cattle serum

Background

Akabane disease (AD), a barrier to international trade for endemic areas with far economic impact on the countries, is caused by Akabane virus (AKAV). Commercial enzyme-linked immunosorbent assay (ELISA) is a commonly used diagnostic technique for AKAV infection, including the IDEXX and IDVET ELISA kits. However, the comparative evaluation of the IDEXX and IDVET ELISA kits has not been published. The object of this study was to evaluate the test performance of the two commercial ELISA kits in detecting serum anti-AKAV antibodies in cattle.

Results

With virus neutralization test (VNT) as the “relative gold standard”, the diagnostic sensitivity (DSe) was 80.39% (123/153) and 93.46% (143/153) for the IDEXX and IDVET ELISA kit, when suspect samples were included. The diagnostic specificity (DSp) for the IDEXX and IDVET ELISA kit was 93.48% (502/537) and 82.31% (442/537), respectively.

Conclusion

Both of the tested ELISA kits could be applied to detect antibodies against AKAV in cattle serum. The IDVET ELISA kit had a higher DSe. The IDEXX ELISA kit possessed the higher DSp. These results have important implications if the kits are used to screen herds or individual cattle in surveillance programs, or at border crossings for import-export inspection and quarantine.

Experimental Infection of Goats with a Newly Isolated Strain of Akabane Virus that Causes Encephalomyelitis

In 2010, there was a large-scale outbreak of bovine encephalomyelitis in Korea, and 15 new strains of Akabane virus (AKAV) were isolated. To identify the pathogenicity of one of these strains, we infected adult goats with AKAV-7 via different routes. Twenty-five female goats were used in this study and were divided into five groups: intracerebral (IC) and intrasubarachnoid (IS) viral inoculation (n = 8 each), intravenous (IV) inoculation (n = 4), and vaccinated before IV inoculation (n = 4), in addition to a negative control animal. All animals inoculated with AKAV-7 had AKAV-neutralizing antibodies at 6-8 days post infection (dpi). During the experimental period, infected animals showed no clinical signs. In the IC group, 5/8 goats had non-suppurative encephalomyelitis affecting the cerebrum. Virus S RNA segments were detected in nearly all areas of the brain. In the IS group, 3/8 goats had encephalomyelitis affecting the cerebrum, cerebellum and spinal cord. At 7 and 21 dpi, virus S RNA segments were found mostly in the spinal cord, especially around the area of injection (L5-L6). Antibody titres in the serum of the vaccinated group had an early onset and slightly increased titre compared with the IV group. Histopathologically, there were no obvious lesions in the central nervous tissues in the vaccinated group, while one of four goats in the IV group showed encephalomyelitis in the parietal lobe of the cerebrum. The newly isolated AKAV-7 can cause encephalomyelitis in goats after experimental injection. The attenuated AKAV vaccine currently used in Korea may provide partial protective immunity against AKAV-7 infection, but the real effect of the vaccine requires further investigation in goats.

An Overview of Animal Models for Arthropod-Borne Viruses

Arthropod-borne viruses (arboviruses) have continued to emerge in recent years, posing a significant health threat to millions of people worldwide. The majority of arboviruses that are pathogenic to humans are transmitted by mosquitoes and ticks, but other types of arthropod vectors can also be involved in the transmission of these viruses. To alleviate the health burdens associated with arbovirus infections, it is necessary to focus today's research on disease control and therapeutic strategies. Animal models for arboviruses are valuable experimental tools that can shed light on the pathophysiology of infection and will enable the evaluation of future treatments and vaccine candidates. Ideally an animal model will closely mimic the disease manifestations observed in humans. In this review, we outline the currently available animal models for several viruses vectored by mosquitoes, ticks, and midges, for which there are no standardly available vaccines or therapeutics.