Advances in canine distemper virus pathogenesis research: a wildlife perspective.

Canine distemper virus (CDV) has emerged as a significant disease of wildlife, which is highly contagious and readily transmitted between susceptible hosts. Initially described as an infectious disease of domestic dogs, it is now recognized as a global multi-host pathogen, infecting and causing mass mortalities in a wide range of carnivore species. The last decade has seen the effect of numerous CDV outbreaks in various wildlife populations. Prevention of CDV requires a clear understanding of the potential hosts in danger of infection as well as the dynamic pathways CDV uses to gain entry to its host cells and its ability to initiate viral shedding and disease transmission. We review recent research conducted on CDV infections in wildlife, including the latest findings on the causes of host specificity and cellular receptors involved in distemper pathogenesis.

Rift Valley Fever Outbreak in Livestock, Mozambique, 2014.

In early 2014, abortions and death of ruminants were reported on farms in Maputo and Gaza Provinces, Mozambique. Serologic analysis and quantitative and conventional reverse transcription PCR confirmed the presence of Rift Valley fever virus. The viruses belonged to lineage C, which is prevalent among Rift Valley fever viruses in southern Africa.

Transovarial passage and transmission of LSDV by Amblyomma hebraeum, Rhipicephalus appendiculatus and Rhipicephalus decoloratus.

Lumpy skin disease (LSD), an acute, sub-acute or inapparent disease of cattle, is caused by lumpy skin disease virus (LSDV), a member of the genus Capripoxvirus in the family Poxviridae. LSD is characterised by high fever, formation of circumscribed skin lesions and ulcerative lesions on the mucous membranes of the mouth, respiratory and digestive tracts. It is an economically important disease due to the permanent damage to hides, the reduction in productivity and trade restrictions imposed on affected areas. Transmission has been associated with blood-feeding insects such as stable flies (Stomoxysis calcitrans) and mosquitoes (Aedes aegypti). Mechanical (intrastadial) and transstadial transmission by Amblyomma hebraeum and Rhipicephalus appendiculatus as well as transovarial transmission by R. decoloratus have been reported. In this study transovarial passage of LSDV to larvae and subsequent transmission to recipient animals were demonstrated. The finding of transovarial passage of LSDV in female ticks shows the potential for A. hebraeum, R. appendiculatus and R. decoloratus to be reservoir hosts for LSDV.

Bluetongue: a historical and epidemiological perspective with the emphasis on South Africa.

Bluetongue (BT) is a non-contagious, infectious, arthropod transmitted viral disease of domestic and wild ruminants that is caused by the bluetongue virus (BTV), the prototype member of the Orbivirus genus in the family Reoviridae. Bluetongue was first described in South Africa, where it has probably been endemic in wild ruminants since antiquity. Since its discovery BT has had a major impact on sheep breeders in the country and has therefore been a key focus of research at the Onderstepoort Veterinary Research Institute in Pretoria, South Africa. Several key discoveries were made at this Institute, including the demonstration that the aetiological agent of BT was a dsRNA virus that is transmitted by Culicoides midges and that multiple BTV serotypes circulate in nature. It is currently recognized that BT is endemic throughout most of South Africa and 22 of the 26 known serotypes have been detected in the region. Multiple serotypes circulate each vector season with the occurrence of different serotypes depending largely on herd-immunity. Indigenous sheep breeds, cattle and wild ruminants are frequently infected but rarely demonstrate clinical signs, whereas improved European sheep breeds are most susceptible. The immunization of susceptible sheep remains the most effective and practical control measure against BT. In order to protect sheep against multiple circulating serotypes, three pentavalent attenuated vaccines have been developed. Despite the proven efficacy of these vaccines in protecting sheep against the disease, several disadvantages are associated with their use in the field.

Detection of Rift Valley Fever Virus in Aedes (Aedimorphus) durbanensis, South Africa.

Rift Valley fever virus (RVFV) is a mosquito-borne, zoonotic phlebovirus-causing disease in domestic ruminants and humans in Africa, the Arabian Peninsula and some Indian Ocean islands. Outbreaks, characterized by abortion storms and a high morbidity rate in newborn animals, occur after heavy and prolonged rainfalls favouring the breeding of mosquitoes. However, the identity of the important mosquito vectors of RVFV is poorly known in most areas. Mosquitoes collected in the Ndumo area of tropical north-eastern KwaZulu-Natal (KZN), South Africa, were tested for RVFV nucleic acid using RT-PCR. The virus was detected in a single pool of unfed Aedes (Aedimorphus) durbanensis, indicating that this seasonally abundant mosquito species could serve as a vector in this area of endemic RVFV circulation. Phylogenetic analysis indicated the identified virus is closely related to two isolates from the earliest outbreaks, which occurred in central South Africa more than 60 years ago, indicating long-term endemicity in the region. Further research is required to understand the eco-epidemiology of RVFV and the vectors responsible for its circulation in the eastern tropical coastal region of southern Africa.

Insights into the Pathogenesis of Viral Haemorrhagic Fever Based on Virus Tropism and Tissue Lesions of Natural Rift Valley Fever.

Rift Valley fever phlebovirus (RVFV) infects humans and a wide range of ungulates and historically has caused devastating epidemics in Africa and the Arabian Peninsula. Lesions of naturally infected cases of Rift Valley fever (RVF) have only been described in detail in sheep with a few reports concerning cattle and humans. The most frequently observed lesion in both ruminants and humans is randomly distributed necrosis, particularly in the liver. Lesions supportive of vascular endothelial injury are also present and include mild hydropericardium, hydrothorax and ascites; marked pulmonary congestion and oedema; lymph node congestion and oedema; and haemorrhages in many tissues. Although a complete understanding of RVF pathogenesis is still lacking, antigen-presenting cells in the skin are likely the early targets of the virus. Following suppression of type I IFN production and necrosis of dermal cells, RVFV spreads systemically, resulting in infection and necrosis of other cells in a variety of organs. Failure of both the innate and adaptive immune responses to control infection is exacerbated by apoptosis of lymphocytes. An excessive pro-inflammatory cytokine and chemokine response leads to microcirculatory dysfunction. Additionally, impairment of the coagulation system results in widespread haemorrhages. Fatal outcomes result from multiorgan failure, oedema in many organs (including the lungs and brain), hypotension, and circulatory shock. Here, we summarize current understanding of RVF cellular tropism as informed by lesions caused by natural infections. We specifically examine how extant knowledge informs current understanding regarding pathogenesis of the haemorrhagic fever form of RVF, identifying opportunities for future research.

Refined experimental design may increase the value of murine models for estimation of bluetongue virus virulence.

Bluetongue is a serious non-contagious vector-borne viral disease in ruminants, causing poor animal welfare and economic consequences globally. Concern has been raised about the development of novel bluetongue virus (BTV) strains and their possibly altered virulence through the process of viral reassortment. Virulence is traditionally estimated in lethal dose 50 (LD50) studies in murine models, but agreement with both in vitro and virulence in ruminants is questionable, and a refined experimental design is needed. Specific reassortants between wild-type and vaccine strains of BTV-1, -6 and -8 have previously been developed by reverse genetics. The aim of the present study was to rank the in vivo virulence of these parental and reassortant BTV strains by calculating LD50 in a murine model by using an experimental design that is new to virology: a between-patient optimised three-level response surface pathway design. The inoculation procedure was intracranial. Fifteen suckling mice were used to establish LD50 for each strain. Three parental and five reassortant virus strains were included. The LD50s varied from of 0.1 (95% confidence interval (CI) 0-0.20) to 3.3 (95% CI 2.96-3.72) tissue culture infectious dose 50/ml. The results support the hypothesis that reassortment in BTV may lead to increased virulence in mice with potential negative consequences for the natural ruminant host. The ranking showed low agreement with in vitro properties and virulence in ruminants according to existing literature. Refined design such as response surface pathway design was found suitable for use in virology, and it introduces significant ethical and scientific improvements.

Babesia lengau sp. nov., a novel Babesia species in cheetah (Acinonyx jubatus, Schreber, 1775) populations in South Africa.

In a previous paper, we reported on a large number of cheetah blood specimens that gave positive signals only for Babesia and/or Theileria genus-specific probes on the reverse line blot (RLB) assay, indicating the presence of a novel species or variant of an existing species. Some of these specimens were investigated further by microscopic, serological, sequencing, and phylogenetic analyses. The near-full-length 18S rRNA genes of 13 samples, as well as the second internal transcribed spacer (ITS2) region, were amplified, cloned, and sequenced. A species-specific RLB probe, designed to target the hypervariable V4 region of the 18S rRNA gene for detection of the novel Babesia sp., was used to screen an additional 137 cheetah blood specimens for the presence of the species. The prevalence of infection was 28.5%. Here we describe the morphology and phylogenetic relationships of the novel species, which we have named Babesia lengau sp. nov.

Complete Genome Sequences of Virus Strains Isolated from Bottle A of the South African Live Attenuated Bluetongue Virus Vaccine.

This is a report of the complete genome sequences of plaque-selected isolates of five virus strains included in bottle A of the South African Onderstepoort Biological Products commercial live attenuated bluetongue virus vaccine.

Neutralizing antibodies against Rift Valley fever virus in wild antelope in far northern KwaZulu-Natal, South Africa, indicate recent virus circulation.

Rift Valley fever (RVF) is a zoonotic viral disease of domestic ruminants in Africa and the Arabian Peninsula caused by a mosquito-borne Phlebovirus. Outbreaks in livestock and humans occur after heavy rains favour breeding of vectors, and the virus is thought to survive dry seasons in the eggs of floodwater-breeding aedine mosquitoes. We recently found high seroconversion rates to RVF virus (RVFV) in cattle and goats, in the absence of outbreaks, in far northern KwaZulu-Natal (KZN), South Africa. Here, we report the prevalence of, and factors associated with, neutralizing antibodies to RVFV in 326 sera collected opportunistically from nyala (Tragelaphus angasii) and impala (Aepyceros melampus) culled during 2016-2018 in two nature reserves in the same area. The overall seroprevalence of RVFV, determined using the serum neutralization test, was 35.0% (114/326; 95%CI: 29.8%-40.4%) and tended to be higher in Ndumo Game Reserve (11/20; 55.0%; 95%CI: 31.5%-76.9%) than in Tembe Elephant Park (103/306; 33.6%; 95%CI: 28.4%-39.3%) (p = .087). The presence of antibodies in juveniles (6/21; 28.6%; 95%CI: 11.3%-52.2%) and sub-adults (13/65; 20.0%; 95%CI: 11.1%-37.8%) confirmed that infections had occurred at least until 2016, well after the 2008-2011 RVF outbreaks in South Africa. Odds of seropositivity was higher in adults than in sub-adults (OR = 3.98; 95%CI: 1.83-8.67; p = .001), in males than in females (OR = 2.66; 95%CI: 1.51-4.68; p = .001) and in animals collected ≤2 km from a swamp or floodplain compared with those collected further away (OR = 3.30; 95%CI: 1.70-6.38; p < .001). Under similar ecological conditions, domestic and wild ruminants may play a similar role in maintenance of RVFV circulation and either or both may serve as the mammalian host in a vector-host reservoir system. The study confirms the recent circulation of RVFV in the tropical coastal plain of northern KZN, providing the basis for investigation of factors affecting virus circulation and the role of wildlife in RVF epidemiology.

Evaluating African horse sickness virus in horses and field-caught Culicoides biting midges on the East Rand, Gauteng Province, South Africa.

A prospective study was undertaken during 2013 and 2014, to determine the prevalence of African horse sickness virus (AHSV) in Culicoides midges and the incidence of infection caused by the virus in 28 resident horses on two equine establishments on the East Rand, Gauteng Province, South Africa. Field caught Culicoides midges together with whole blood samples from participating horses were collected every two weeks at each establishment. Culicoides midges and blood samples were tested for the presence of AHSV RNA by real-time quantitative reverse transcription polymerase chain reaction. Nine immunised horses became infected with AHSV during the study period, although infections were subclinical. African horse sickness virus was also identified from a field-collected midge pool. The observations recapitulate previously published data in another setting, where further investigation is warranted to determine what role subclinical infection plays in the diseases epidemiology.

Phylogenetic Characterization of the Palyam Serogroup Orbiviruses.

The Palyam serogroup orbiviruses are associated with abortion and teratogenesis in cattle and other ruminants. Of the 13 different serotypes that have been identified, the full genome sequence of only one, Kasba, has been published. We undertook to perform Next Generation Sequencing (NGS) and phylogenetic analysis on 12 Palyam serotypes plus field isolates of the African serotypes in our possession. The Palyam serogroup was found to be most closely related to the African horse sickness virus group and showed the most distant evolutionary relationship to the equine encephalosis viruses (EEV). Amino acid sequence analysis revealed that the gene encoding VP7 was the most conserved within serotypes and VP2 and VP5 showed the highest degree of variation. A high degree of sequence identity was found for isolates from the same geographical region. The phylogenetic analysis revealed two clades where the African serotypes were all very closely related in one clade and the other clade contained the Australian and Asian serotypes and one African serotype, Petevo. It was evident from the sequence data that the geographical origin of Palyam serogroup viruses played an important role in the development of the different serotypes.

High seroconversion rate to Rift Valley fever virus in cattle and goats in far northern KwaZulu-Natal, South Africa, in the absence of reported outbreaks.

BACKGROUND: Rift Valley fever (RVF) is a mosquito-borne zoonotic disease characterized in South Africa by large epidemics amongst ruminant livestock at very long, irregular intervals, mainly in the central interior. However, the presence and patterns of occurrence of the virus in the eastern parts of the country are poorly known. This study aimed to detect the presence of RVF virus (RVFV) in cattle and goats in far northern KwaZulu-Natal province and to estimate the prevalence of antibodies to the virus and the incidence rate of seroconversion. METHODOLOGY: Cross-sectional studies were performed in communally farmed cattle (n = 423) and goats (n = 104), followed by longitudinal follow-up of seronegative livestock (n = 253) 14 times over 24 months, representing 160.3 animal-years at risk. Exposure to RVFV was assessed using an IgG sandwich ELISA and a serum neutralization test (SNT) and seroconversion was assessed using SNT. Incidence density was estimated and compared using multivariable Poisson models and hazard of seroconversion was estimated over time. PRINCIPAL FINDINGS: Initial overall seroprevalence was 34.0% (95%CI: 29.5-38.8%) in cattle and 31.7% (95%CI: 22.9-41.6%) in goats, varying by locality from 18-54%. Seroconversions to RVFV based on SNT were detected throughout the year, with the incidence rate peaking during the high rainfall months of January to March, and differed considerably between years. Overall seroconversion rate in cattle was 0.59 per animal-year (95% CI: 0.46-0.75) and in goats it was 0.41 per animal-year (95% CI: 0.25-0.64), varying significantly over short distances. CONCLUSIONS/SIGNIFICANCE: The high seroprevalence in all age groups and evidence of year-round viral circulation provide evidence for a hyperendemic situation in the study area. This is the first study to directly estimate infection rate of RVFV in livestock in an endemic area in the absence of reported outbreaks and provides the basis for further investigation of factors affecting viral circulation and mechanisms for virus survival during interepidemic periods.

Effect of using frozen-thawed bovine semen contaminated with lumpy skin disease virus on in vitro embryo production.

Lumpy skin disease (LSD) is an important transboundary animal disease of cattle with significant economic impact because of the implications for international trade in live animals and animal products. LSD is caused by a Capripoxvirus, LSD virus (LSDV), and results in extensive hide and udder damage, fever and pneumonia. LSDV can be shed in semen of infected bulls for prolonged periods and transmitted venereally to cows at high doses. This study examined the effects of LSDV in frozen-thawed semen on in vitro embryo production parameters, including viral status of media and resulting embryos. Bovine oocytes were harvested from abattoir-collected ovaries and split into three experimental groups. After maturation, the oocytes were fertilized in vitro with frozen-thawed semen spiked with a high (HD) or a lower (LD) dose of LSDV, or with LSDV-free semen (control). Following day 7 and day 8 blastocyst evaluation, PCR and virus isolation were performed on all embryonic structures. After completing sufficient replicates to reach 1,000 inseminated oocytes, further in vitro fertilization (IVF) runs were performed to provide material for electron microscopy (EM) and embryo washing procedures. Overall, in vitro embryo yield was significantly reduced by the presence of LSDV in frozen-thawed semen, irrespective of viral dose. When semen with a lower viral dose was used, significantly lower oocyte cleavage rates were observed. LSDV could be detected in fertilization media and all embryo structures, when higher doses of LSDV were present in the frozen-thawed semen used for IVF. Electron microscopy demonstrated LSDV virions inside blastocysts. Following the International Embryo Transfer Society washing procedure resulted in embryos free of viral DNA; however, this may be attributable to a sampling dilution effect and should be interpreted with caution. Further research is required to better quantify the risk of LSDV transmission via assisted reproductive procedures.

Reassortment of bluetongue virus vaccine serotypes in cattle.

Bluetongue is primarily a disease of sheep in South Africa, while cattle and goats are mostly subclinically infected. The viraemia of bluetongue virus in cattle lasts much longer than in sheep and the role of cattle in the epidemiology of bluetongue in South Africa is poorly understood. Bluetongue virus has a segmented double-stranded ribonucleic acid genome and reassortment of genomes is a common feature. The aim of the study was to investigate whether reassortment occurs between vaccine and field strains when simultaneously administered to cattle. Six cattle between the ages of 6 and 12 months were infected with five strains of modified live vaccine bluetongue virus and a virulent field isolate of bluetongue virus 4. Blood samples were subsequently collected daily from these animals from day 1 to day 39 post-inoculation. Viruses were directly isolated during viraemia from the buffy coat on Vero cells using the plaque forming unit method. Analysis of plaques indicated that no reassortants between virulent field and vaccine strains occurred and the virulent bluetongue virus 4 was identified as the predominant virus strain. However, a reassortant virus between two bluetongue virus vaccine strains was isolated from the buffy coat. Whole genome sequences from the vaccine viruses were compared to the suspected reassortant and it was found that segment 8 exchanged between the bluetongue virus 8 and bluetongue virus 9 vaccine strains. The use of the live-attenuated bluetongue virus multivalent vaccine in South Africa causes circulation of different vaccine serotypes in Culicoides spp. and susceptible hosts and cattle might provide the ideal host for reassortment to occur.

Phylogenetic analysis of canine distemper virus in South African wildlife.

Canine distemper virus (CDV) causes a severe contagious disease in a broad range of hosts. This is the first study to genetically characterise CDV strains from four different wildlife species in South Africa. The phylogenetic diversity of CDV is examined, using the haemagglutinin gene. The South African wildlife CDV isolates showed a high degree of similarity to CDV in South African domestic dogs. Phylogenetic analyses confirmed the presence of 12 geographical lineages with CDV strains from South African wildlife falling within the Southern African lineage. The study reveals two possible co-circulating sub-genotypes corresponding to the northern and southern regions of South Africa respectively. CDV strains from the non-canid species were distinct, but similar to CDV isolates from domestic dog and wild canids. Residues at amino acid sites of the SLAM binding region support the notion that CDV strains encoding 519I / 549H are better adapted to non-canid species than canid species. The amino acids present at site 530 are conserved regardless of host species. Strains from South African wild carnivores showed no difference between host species with all strains presenting 530N. All non-canid strains in this study presented the combination 519I/549H. No evidence of host adaptation or lineage grouping was observed for the Nectin-4 binding region. Further studies should include CDV strains isolated from various hosts from a wider geographical range in South Africa.

Effect of semen processing methods on lumpy skin disease virus status in cryopreserved bull semen.

Lumpy skin disease is an economically important disease of cattle, caused by the lumpy skin disease virus (LSDV; Capripoxvirus). It has a variable clinical appearance but, in severely affected animals, is associated with extensive skin damage, pneumonia and death. The LSDV can be found in the semen of infected bulls for prolonged periods of time, from where it can be transmitted by mating or artificial insemination and cause clinical disease in heifers and cows. In this study, an ejaculate was collected from a LSDV seronegative bull and confirmed free from LSDV DNA by PCR. The ejaculate was split into a control sample (C), a sample spiked with a 4 log TCID50 dose of an LSDV isolate (HD) and a 103 dilution of the virus suspension (ND) and frozen routinely. Two straws from each of the different semen treatment groups (HD, ND and C) were subsequently thawed and subjected to swim-up, single layer centrifugation, Percoll® density gradient and a Percoll® density gradient with added trypsin. For one set of straws, semen quality variables were recorded, and viral DNA status determined using PCR; the other set was used for positive staining electron microscopy. Samples determined to be positive for LSDV DNA by PCR were then subjected to virus isolation (VI). Complete elimination of LSDV from semen did not occur with use of any of the processing methods. Trypsin did reduce the viral load, and eliminated LSDV from the ND sample, but severely negatively influenced semen quality. The LSDV virions, as assessed by electron microscopy, were associated with the sperm plasma membrane. Further investigation is needed to establish the efficacy of immuno-extenders for rendering semen free from LSDV.

Genome Sequences of Three Vaccine Strains and Two Wild-Type Canine Distemper Virus Strains from a Recent Disease Outbreak in South Africa.

Canine distemper virus causes global multihost infectious disease. This report details complete genome sequences of three vaccine and two new wild-type strains. The wild-type strains belong to the South African lineage, and all three vaccine strains to the America 1 lineage. This constitutes the first genomic sequences of this virus from South Africa.

Complete Genome Sequences of Five Bluetongue Virus (BTV) Vaccine Strains from a Commercial Live Attenuated Vaccine, a BTV-4 Field Strain from South Africa, and a Reassortant Strain Isolated from Experimentally Vaccinated Cattle.

This is a report of the complete genome sequences of plaque-selected isolates of each of the five virus strains included in a South African commercial trivalent bluetongue virus (BTV) attenuated live virus vaccine, a BTV-4 field strain isolated from Rustenburg, South Africa, in 2011, and a bluetongue reassortant (bluetongue virus 4 strain 4/O. aries-tc/ZAF/11/OBP-115) isolated from experimentally vaccinated cattle. Full-genome sequencing and phylogenetic analyses show that the bluetongue virus 9 strain 9/B. taurus-tc/ZAF/15/Onderstepoort_B02b is a reassortant virus containing segments from both BTV-9 and BTV-8.

Possible over-wintering of bluetongue virus in Culicoides populations in the Onderstepoort area, Gauteng, South Africa.

Several studies have demonstrated the ability of certain viruses to overwinter in arthropod vectors. The over-wintering mechanism of bluetongue virus (BTV) is unknown. One hypothesis is over-wintering within adult Culicoides midges (Diptera; Ceratopogonidae) that survive mild winters where temperatures seldom drop below 10 °C. The reduced activity of midges and the absence of outbreaks during winter may create the impression that the virus has disappeared from an area. Light traps were used in close association with horses to collect Culicoides midges from July 2010 to September 2011 in the Onderstepoort area, in Gauteng Province, South Africa. More than 500 000 Culicoides midges were collected from 88 collections and sorted to species level, revealing 26 different Culicoides species. Culicoides midges were present throughout the 15 month study. Nine Culicoides species potentially capable of transmitting BTV were present during the winter months. Midges were screened for the presence of BTV ribonucleic acid (RNA) with the aid of a real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR) assay. In total 91.2% of midge pools tested positive for BTV RNA. PCR results were compared with previous virus isolation results (VI) that demonstrated the presence of viruses in summer and autumn months. The results indicate that BTV-infected Culicoides vectors are present throughout the year in the study area. Viral RNA-positive midges were also found throughout the year with VI positive midge pools only in summer and early autumn. Midges that survive mild winter temperatures could therefore harbour BTV but with a decreased vector capacity. When the population size, biting rate and viral replication decrease, it could stop BTV transmission. Over-wintering of BTV in the Onderstepoort region could therefore result in re-emergence because of increased vector activity rather than reintroduction from outside the region.