Topic:African Horse Sickness
African Horse Sickness (AHS) is a viral disease affecting equines, caused by the African Horse Sickness Virus (AHSV), which is an orbivirus transmitted primarily by Culicoides midges. The disease is characterized by clinical signs such as fever, respiratory distress, and edema, with varying degrees of severity depending on the form of the disease. AHS is endemic to sub-Saharan Africa but poses a risk of outbreaks in other regions due to the movement of infected animals and vectors. The disease has significant implications for equine health and management due to its high mortality rate in susceptible populations. This page compiles peer-reviewed research studies and scholarly articles that explore the epidemiology, pathogenesis, clinical presentation, and control measures of African Horse Sickness in horses.
Application of the polymerase chain reaction to the detection of African horse sickness viruses. The development of a coupled reverse transcriptase-polymerase chain reaction assay (RT-PCR) is described for the detection of African horse sickness virus (AHSV) double-stranded RNA. Genome segments 7 and 10 were chosen as target templates for primers selected for use in the RT-PCR. Using these AHSV-specific primers all 9 serotypes were detectable. The sensitivity and specificity of the RT-PCR results were compared to those obtained by competition ELISA.
Clinical pathology and hemostatic abnormalities in experimental African horsesickness. Infection of naive North American horses with 10(4) cell culture infectious doses (CCID50) of virulence variants of African horsesickness virus (AHSV), designated AHSV/4SP, AHSV/9PI, and AHSV/4PI, reproduced three classical forms of African horsesickness: acute (pulmonary), subacute (cardiac), and febrile, respectively. Distinct clinicopathologic and hemostatic abnormalities were associated with each form of disease. Hemostatic abnormalities included increased concentration of fibrin degradation products and prolongation of prothrombin, activated partial thromboplastin, and thrombin clotting t...
The transmission and geographical spread of African horse sickness and bluetongue viruses. African horse sickness virus (AHSV) and bluetongue virus (BTV) are dsRNA viruses within the genus Orbivirus. Both are able to cause non-contagious, infectious arthropod-borne diseases in their respective vertebrate hosts. AHSV infects equines and occasionally dogs, whereas BTV replicates in ruminants. The disease caused by AHSV is usually at its most severe in horses, whereas certain breeds of sheep are particularly sensitive to BTV infection. AHSV is endemic in sub-Saharan Africa but periodically makes brief excursions beyond this area. BTV occurs much more widely and can be found in a band a...
Continuing prevalence of African horse sickness in Nigeria. Equine sera collected from 10 widely separated regions throughout Nigeria were tested for antibodies against African horse sickness viruses (AHSV) using a competitive enzyme-linked immunosorbent assay (ELISA). The animals sampled included imported, exotic horses, indigenous and locally cross-bred (local) horses and African donkeys. A high percentage of the sera (79.8%) were positive, confirming the continued prevalence of AHSV antibodies in Nigerian horses and donkeys.
Epidemiology of African horsesickness: duration of viraemia in zebra (Equus burchelli). The viraemic period of African horsesickness is significantly longer in experimentally infected zebra than in horses. The virus could be isolated 40 d post-infection from blood and 48 d post-infection from spleen. The introduction of zebra into African horsesickness-free countries should therefore be considered carefully, and preferably be restricted to serologically negative zebra.
Nematocera (Ceratopogonidae, Psychodidae, Simuliidae and Culicidae) and control methods. The biology, veterinary importance and control of certain Nematocera are described and discussed. Culicoides spp. (family Ceratopogonidae) transmit the arboviruses of bluetongue (BT), African horse sickness (AHS), bovine ephemeral fever (BEF) and Akabane. Some other arboviruses have been isolated from these species, while fowl pox has been transmitted experimentally by Culicoides. These insects are vectors of the parasitic protozoans Leucocytozoon caulleryi and Haemoproteus nettionis, and the parasitic nematodes Onchocerca gutturosa, O. gibsoni and O. cervicalis. They also cause recurrent summ...
Presence of African horse sickness virus in equine tissues, as determined by in situ hybridization. In a retrospective study, a negative-sense digoxigenin-labeled RNA probe, corresponding to the gene encoding nonstructural protein-1 of African horse sickness virus (AHSV) serotype 4, was applied to formalin-fixed, paraffin-embedded tissue taken from horses in the terminal stages of infection with AHSV. Fifteen infected ponies and one noninfected control were studied. Ponies exhibited a range of clinical signs and lesions. Thirteen ponies were infected with serotype 4, one with serotype 1, and one with serotype 2. Ponies were monitored clinically and euthanatized when severely clinically ill. ...
African horse sickness and the overwintering of Culicoides spp. in the Iberian peninsula. The presence at different latitudes and the seasonal distribution of two known or potential vectors of African horse sickness (AHS) virus--Culicoides imicola and C. obsoletus--were investigated in the Iberian peninsula using light trap collections. Culicoides imicola was present as far north as 41 degrees N but not at 43 degrees N (Asturias, Spain), whereas C. obsoletus was found at all latitudes. In the northern part of the distribution of C. imicola, adults of this species were present for only a few months of the year, but adults were continually present further south. Culicoides obsoletus ...
Diagnosis of African horsesickness. African horsesickness (AHS) is a very serious, non-contagious disease of horses and other solipeds caused by an arthropod-borne orbivirus of the family Reoviridae. The epizootic nature of the disease makes rapid, accurate diagnosis of AHS absolutely essential. Currently, diagnosis of AHS is based on typical clinical signs and lesions, a history consistent with vector transmission and confirmation by laboratory detection of virus and/or anti-AHS virus antibodies. The clinicopathologic presentation of AHS, current and next generation laboratory diagnostic methods are discussed.
African horsesickness: pathogenesis and immunity. African horsesickness (AHS) is a serious, non-contagious disease of horses and other solipeds caused by an arthropod-borne orbivirus of the family Reoviridae. In horses, AHS causes three distinct clinicopathologic syndromes, the pulmonary, cardiac and fever forms of the disease. Recent work has shown that the primary determinant of the form of disease expressed by naive horses is the virulence of the virus inoculum. Horses which recover from AHS exhibit solid humoral immunity against homologous challenge. Protective antibodies appear to be directed towards neutralizing epitopes on AHS virus VP...
Epizootiology and vectors of African horse sickness virus. African horse sickness (AHS) virus causes a non-contagious, infectious, arthropod-borne disease of equines and is enzootic in sub-Saharan Africa. The major vectors are species of Culicoides but mosquitoes and ticks may be involved. Periodically the virus makes excursions beyond its enzootic zones but until recently has not been able to maintain itself outside these areas for more than 2-3 consecutive years. This is probably due to a number of factors including the absence of a long term vertebrate reservoir, the prevalence and seasonal incidence of the vectors and the efficiency of control mea...
Expression and characterization of the two outer capsid proteins of African horsesickness virus: the role of VP2 in virus neutralization. African horsesickness virus (AHSV) is a gnat-transmitted member of the Orbivirus genus of the Reoviridae family. The virus has a genome of 10 double-stranded RNA species (L1-L3, M4-M6, S7-S10). The L2 and M6 genes of AHSV serotype 4 (AHSV-4) which encode the outer capsid proteins VP2 and VP5, respectively, were inserted into recombinant baculoviruses downstream of the baculovirus polyhedrin, or p10 promoters. Recombinant baculoviruses expressing VP2, VP5, or VP2 and VP5 proteins of AHSV-4 were isolated. The expressed AHSV proteins were similar in size and antigenic properties to those of viral...
Detection of African horsesickness virus by reverse transcriptase polymerase chain reaction (RT-PCR) using primers for segment 5 (NS1 gene). The reverse transcription followed by the polymerase chain reaction (RT-PCR) technique was applied to the detection of African horsesickness virus (AHSV) using primers specific for attenuated AHSV serotype 4 segment 5 (NS1 gene). Total RNA which contains both messenger RNA and genomic dsRNA was extracted by the acid guanidinium-phenol-chloroform method from the AHSV infected Vero cells and was used as templates to optimize the RT-PCR. A pair of primer (NP2-NP32) amplified the product of the expected size from all serotypes of attenuated AHSV when four pairs of primers were tested. Using this p...
Detection of African horse sickness virus by reverse transcription-PCR. Reverse transcription-PCR (RT-PCR) was used to detect African horse sickness virus (AHSV). A single primer pair which amplified a 423-bp fragment of the S8 gene which encodes the NS2 protein of AHSV was identified. Amplification of this fragment from all nine serotypes of AHSV was achieved with these primers. Between 10(1) and 10(2) copies of AHSV genomic double-stranded RNA could be detected by RT-PCR followed by agarose gel electrophoresis and ethidium bromide staining. Application of RT-PCR to blood samples from AHSV-infected horses resulted in earlier detection of viremia than virus isolat...
Further studies on the efficacy of an inactivated African horse sickness serotype 4 vaccine. The immunity induced by two inoculations of a commercial inactivated African horse sickness (AHS) serotype 4 (AHSV-4) vaccine was studied. No adverse reaction was observed in five horses following vaccination. Following challenge-inoculation, no clinical signs attributable to AHS, no viraemia indicating infection, and no anamnestic response was observed in the vaccinated ponies. Two control ponies developed clinical signs typical of AHS, high levels of viraemia, and died 7 and 8 days postchallenge-inoculation. The quality of immunity induced by the two-dose regimen was compared with a one-dose...
Diagnosis of the African horse sickness virus serotype 4 by a one-tube, one manipulation RT-PCR reaction from infected organs. A single tube reverse transcription-polymerase chain reaction (RT-PCR) method for detection of African horse sickness virus (AHSV) in splenic tissues from infected horses is described. Double stranded RNA was extracted from infected organs of horses and used to produce complementary DNA (cDNA) with the two primers selected for the PCR. The 1179 bp amplified product (the segment 7 which encodes for VP 7), detected by electrophoresis on agarose gel and ethidium bromide staining, was hydrolysed with eight restriction endonucleases for characterization of the AHSV. The sensitivity of this method i...
Isolation and identification of African horse sickness virus during an outbreak in Lagos, Nigeria. An outbreak of African horse sickness involving two horse stables in Lagos, Nigeria, was investigated. Inoculation of blood from infected horses into suckling albino mice resulted in isolation of a virus which was identified as African horse sickness virus by the complement fixation test. The clinical, pathological and epizootiological findings (reported elsewhere) were consistent with African horse sickness. Potential threats of the epidemic to international horse trade are briefly highlighted.
African horse sickness. AHS is a noncontagious vector-borne disease of Equidae caused by Orbiviruses. Species susceptibility in decreasing order is horses, mules, donkeys, and zebras. The main vectors of AHS are culicoides. The disease is endemic in sub-Saharan Africa, but epizootics have occurred outside of this area on several occasions. The most recent outbreaks outside of the endemic area were in Spain, Morocco, and Portugal between 1987 and 1990. AHS causes mortality up to 95% and is classically divided into four clinical forms: the pulmonary, cardiac, mixed, and horse fever forms. Pathologic changes are subcuta...
African horse sickness. AHS is a noncontagious vector-borne disease of Equidae caused by Orbiviruses. Species susceptibility in decreasing order is horses, mules, donkeys, and zebras. The main vectors of AHS are culicoides. The disease is endemic in sub-Saharan Africa, but epizootics have occurred outside of this area on several occasions. The most recent outbreaks outside of the endemic area were in Spain, Morocco, and Portugal between 1987 and 1990. AHS causes mortality up to 95% and is classically divided into four clinical forms: the pulmonary, cardiac, mixed, and horse fever forms. Pathologic changes are subcuta...
African horse sickness. AHS is a noncontagious vector-borne disease of Equidae caused by Orbiviruses. Species susceptibility in decreasing order is horses, mules, donkeys, and zebras. The main vectors of AHS are culicoides. The disease is endemic in sub-Saharan Africa, but epizootics have occurred outside of this area on several occasions. The most recent outbreaks outside of the endemic area were in Spain, Morocco, and Portugal between 1987 and 1990. AHS causes mortality up to 95% and is classically divided into four clinical forms: the pulmonary, cardiac, mixed, and horse fever forms. Pathologic changes are subcuta...
Characterization of virulence variants of African horsesickness virus. There are three clinicopathologic syndromes associated with African horsesickness (AHS) virus infection in horses. These different forms of AHS (pulmonary, cardiac, and fever forms) vary in the organs affected, the severity of lesions, time of onset of clinical signs and mortality rates. We have studied the effects of infection with three cell culture passaged variants of AHS virus in naive North American horses. One of these viruses, AHS/4SP, consistently caused the pulmonary form of AHS with rapid onset of severe pulmonary edema and 100% mortality. A second variant, AHS/9PI, resulted in sign...
African horse sickness. AHS is a noncontagious vector-borne disease of Equidae caused by Orbiviruses. Species susceptibility in decreasing order is horses, mules, donkeys, and zebras. The main vectors of AHS are culicoides. The disease is endemic in sub-Saharan Africa, but epizootics have occurred outside of this area on several occasions. The most recent outbreaks outside of the endemic area were in Spain, Morocco, and Portugal between 1987 and 1990. AHS causes mortality up to 95% and is classically divided into four clinical forms: the pulmonary, cardiac, mixed, and horse fever forms. Pathologic changes are subcuta...
Current status of the diagnosis and control of African horse sickness. African horse sickness (AHS) is an infectious, non-contagious, highly fatal viral disease of Equidae, transmitted by arthropod vectors of the genus Culicoides, and endemic in Africa south and east of the Sahara. The disease is caused by a virus of the Reoviridae family, genus Orbivirus, and 9 serotypes have been recognized. Recent outbreaks of AHS in the Iberian peninsula and Northern Africa emphasize the need for accurate diagnosis and rapid implementation of control measures. In this paper, the epizootiological factors, clinical signs and necropsy findings of AHS are discussed, and an update...
African horse sickness: transmission and epidemiology. African horse sickness (AHS) virus causes a non-contagious, infectious, arthropod-borne disease of equines and occasionally of dogs. The virus is widely distributed across sub-Saharan African where it is transmitted between susceptible vertebrate hosts by the vectors. These are usually considered to be species of Culicoides biting midges but mosquitoes and/or ticks may also be involved to a greater or lesser extent. Periodically the virus makes excursions beyond its sub-Saharan enzootic zones but until recently does not appear to have been able to maintain itself outside these areas for more t...
Group-reactive ELISAs for detecting antibodies to African horsesickness and equine encephalosis viruses in horse, donkey, and zebra sera. Group-reactive enzyme-linked immunosorbent assays (ELISAs) were developed to selectively detect antibodies to African horsesickness virus (AHSV) and equine encephalosis virus (EEV), 2 orbiviruses that infect equids. In indirect ELISA, guinea pig antisera to all known AHSV or EEV serotypes recognized immobilized AHSV serotype 3 or EEV Cascara, respectively. Antisera from naturally infected animals did not cross-react with their respective heterologous viruses. The ELISA was used in parallel with the complement fixation (CF) and agar gel immunodiffusion tests to detect antibodies in sera from an...
Characterization of African horsesickness virus serotype 4-induced polypeptides in Vero cells and their reactivity in Western immunoblotting. The structural and non-structural proteins induced by African horsesickness virus serotype 4 (AHSV-4) in infected Vero cells were analysed by SDS-PAGE. Twenty-two virus-induced polypeptides were detected in infected cells by comparison with the polypeptides of mock-infected cells, of which four major (VP2, VP3, VP5 and VP7) and three minor (VP1, VP4 and VP6) structural proteins and four non-structural proteins (P58, P48, P21 and P20) were shown to be virus-coded, as deduced from electrophoretic and antigenic studies of purified virions and infected cells. The proteins that elicit the major ant...
Recommendations for African horse sickness vaccines for use in nonendemic areas. African horse sickness (AHS), which causes mortality up to 95%, is caused by orbiviruses and is transmitted by Culicoides. The goal of a control and eradication program for AHS is to prevent the spread of the virus via the biological vector. Control measures include slaughter of infected animals, housing of suspected infected animals in insect-proof stalls, and vaccination. Vaccination has played a key role in eradication when AHS occurred outside of Africa. Both modified live vaccines (MLV) and inactivated vaccines have been used to control AHS. An acceptable vaccine should be: safe, efficaci...
Haemagglutination-inhibiting antibodies against African horse sickness virus in domestic animals in Nigeria. A sero-epidemiological survey of African horse sickness (AHS) virus in 261 animals which included 96 camels, 81 horses, 80 dogs and 4 donkeys was carried out in Nigeria. The animals had no history of vaccination against AHS. Sera were tested by the haemagglutination-inhibition (HI) test for the presence of antibody against AHS virus. Of these, 77 (95.1%) horse, 4 (100%) donkey, 10 (10.4%) camel and 28 (35%) dog sera samples tested were recorded as positive. The prevalence of antibody in samples taken from horses in different regions was similar. The prevalence of antibody to AHS virus detected...