Biochemical properties of a 24 kilodalton membrane glycoprotein antigen complex from Schistosoma mansoni.

Antibodies were affinity purified from crude antiserum by elution from the 24 kDa region of preparative one-dimensional Western blots containing immobilized adult Schistosoma mansoni inner bilayer membrane proteins. They were shown to be specific for a single acidic polypeptide complex, Smgp24, following immunoblotting from two-dimensional polyacrylamide gels. These antibodies were then used to detect the presence of the Smgp24 complex in fractions prepared from lectin affinity chromatography, phase separation in Triton X-114 and chemical and enzymatic carbohydrate modification treatments. The 24 kDa antigen was bound and specifically eluted from both concanavalin A and lentil lectin affinity matrices. In addition, the electrophoretic mobility of the antigen was shifted to approximately 20 kDa after treatment with endoglycosidase F and N-glycanase, but was not appreciably altered following treatment with endoglycosidase H, neuraminidase, or sodium meta-periodate. The 20 kDa species produced by endoglycosidase F or N-glycanase treatment no longer bound to the lectin affinity resins. The Smgp24 complex also partitioned almost quantitatively into the detergent-enriched phase after phase separation in Triton X-114 solutions. These results indicate that the Smgp24 complex is an antigenic integral membrane glycoprotein and may consist of a single polypeptide backbone which is extensively post- or co-translationally modified.

Epidemiology of African horse sickness and the role of the zebra in South Africa.

Zebra are the only equine species native to South Africa. These animals roamed over much of the country in the 17th century when horses and donkeys were first imported. The first cases of African horse sickness (AHS) then occurred in the horses of hunters who entered zebra territory. AHS continued to occur on a country-wide basis until the beginning of the 20th century, though the number of outbreaks decreased as the populations of zebra collapsed through overhunting. For most of the 20th century almost all free-living zebra have been confined to the north-eastern parts of South Africa which are now the only areas in the country where AHS is endemic; though when climatic conditions are favourable, temporarily, it spreads beyond these areas. The minimum size of a zebra population necessary to maintain a focus of AHS virus is unknown but the small, isolated populations that have inhabited the majority of South Africa for most of the 20th century are apparently insufficient to maintain the virus in the long term. In this context, the restocking of many parts of the country with zebra should be viewed with caution since conditions may be generated that will facilitate the re-establishment of permanent foci of AHS virus.

Transmission and distribution of African horse sickness virus serotypes in South African zebra.

The prevalences of African horse sickness (AHS) virus serotypes in zebra foals from the Kruger National Park, South Africa were examined for possible associations between serotypes. Serotypes known to cross-react were combined for analysis. The distributions of serotypes between zebra were not always independent; in 7-8 month old zebra positive pairwise associations were observed between 3 serotypes. This could be generated by biological interactions between serotypes or heterogeneity in host-vector transmission. The data were also used to estimate the basic reproduction number, R0. For AHS virus overall, estimates of R0 ranged from 31-68. This underlines the need for a better understanding of serotype transmission and interactions in AHS.

Some factors governing the entry of Culicoides spp. (Diptera: Ceratopogonidae) into stables.

The entry of Culicoides species into stables was examined by comparing the numbers of midges caught with identical light-traps under different conditions. The comparison was made between collections made inside an empty stable, a regularly cleaned stable and a dirty stable and those made outside the stables in a sleeping space open on two sides. The work was first done in the presence of cattle and sheep in adjoining paddocks and then repeated in their absence. A positive correlation was found between the numbers of C. imicola females caught out of doors and inside a clean stable. Removal of the cattle and sheep resulted in a reduction in the numbers of C. imicola caught inside and outside the stables. In contrast, the numbers of Culicoides spp. that prefer to feed on birds was not affected by the removal of the cattle and sheep. Their entry into the stable was proportionate to the size of the entrances into the sleeping space and the size of the stable door and presumably occurs passively. On the other hand, the numbers of C. imicola females entering the same stables were somewhat enhanced by the presence of horses inside the stables and by odours associated with dirty stables.

Antibodies against some viruses of domestic animals in southern African wild animals.

Twenty-four species of South African wild animals were tested for the presence of antibodies against the viruses of 16 common diseases of domestic animals. Positive results were obtained for African horsesickness, equine encephalosis, equid herpes virus-1, infectious bovine rhinotracheitis, Allerton disease (Herpes mammillitis), lumpy skin disease, parainfluenza, encephalomyocarditis, bluetongue, Wesselsbron disease, bovine ephemeral fever, and Akabane disease complex. No antibodies could be demonstrated against the viruses of equine influenza, equine infectious anaemia, equine viral arteritis and Rift Valley fever. The negative results substantiate observations that the latter diseases, with the exception of equine viral arteritis, are absent in South Africa. The number of animal species found positive for a specific virus, ranged from 0-16. No antibodies were found in crocodiles and warthogs, whereas antibodies against Wesselsbron and bovid herpes virus-1 were present in 16 species. Antibodies against viruses of horses were found almost exclusively in zebras and, although elephants reacted to African horsesickness, no neutralizing antibodies against it could be demonstrated in their sera. Zebras were also found to be positive for Wesselsbron and Akabane, which are usually regarded as viruses of ruminants. Antibodies against most viruses were encountered in all vegetation zones in South Africa but, as a rule, most viruses were more prevalent in the high-rainfall zone in KwaZulu-Natal.

Epizootology of wildebeest-derived malignant catarrhal fever: possible transmission among cows and their calves in the north-western Transvaal.

The investigation involved 52 cases of wildebeest-derived malignant catarrhal fever in 1986 and 1989 in a herd of cattle kept in camps adjacent to a game farm harbouring a herd of approximately 330 blue wildebeest (Connochaetes taurinus). In the outbreaks, 34 cows and 18 calves died as result of the disease. The exceptionally high incidence of the disease in both cows and their calves, the low incidence in calves of unaffected cows, the relatively short period between the death of cows and their calves as well as the occurrence of the disease in 2 calves born after their mothers had been moved away from wildebeest, are indicative of transmission among cows and calves. The death of at least 6 calves within 6 weeks of birth is ascribed to intra-uterine infection while some calves that survived longer may have acquired the infection from other cattle or from wildebeest.

Acid production by flavivirus-infected VERO and CER cell cultures.

VERO and CER cell cultures infected with flaviviruses produce more acid than non-infected control cultures. Acid production is dependent on the presence of glucose. This phenomenon can be utilized for the titration of flaviviruses.

Circulation of African horsesickness virus in zebra (Equus burchelli) in the Kruger National Park, South Africa, as measured by the prevalence of type specific antibodies.

In the Kruger National Park 75% of zebra foals are born in October-March and they lose their passive immunity against African horsesickness virus (AHSV) when they are 5-6 months old. One month later infection with different serotypes of AHSV amounts to 31% and thereafter infections increase rapidly to almost 100% before the foals are 12 months old. The capability of zebra to maintain AHSV is clearly illustrated by the continuing infections during every month of the year with a peak period in winter. This peak is ascribed to the presence of large numbers of susceptible foals in the presence of active Culicoides species.

The role played by wildlife in the epizootiology of rabies in South Africa and South-West Africa.

The role played by wildlife in the perpetuation of rabies is discussed in the light of information obtained during a routine examination of specimens at the Veterinary Research Institute, Onderstepoort, during the 10-year period, 1967-1976. In the course of the investigation, 9 additional hosts of rabies were confirmed and 4 rabies areas identified. The chief disseminators in 2 of these areas were found to be the dog (Canis familiaris) and the black-backed jackal (C. mesomelas); in the third area, the yellow mongoose (Cynictis penicillata), and in the fourth Genetta and Felis spp., including the domestic cat (Felis catis). It was noted that the domestic cat is of less importance in those areas where dogs and jackals are the chief disseminators.

Attenuation of turkey meningo-encephalitis virus in BHK21 cells.

Turkey meningo-encephalitis virus was adapted to BHK21 cell culture. Cytopathic effects were characterized by rounding and detachment of cells within 48 hours. Attenuation was achieved by 41 successive passages in BHK21 cell cultures. Turkeys and Japanese quail (Coturnix coturnix japonica), kept under laboratory conditions and inoculated with the attenuated virus, did not develop symptoms of turkey meningo-encephalitis but reacted by the production of haemagglutination inhibition antibody. They resisted intracerebral challenge with pathogenic strains of turkey meningo-encephalitis virus.

A study of the pathology of lumpy skin disease in cattle.

Microscopic lesions in cattle infected with the virus of the Neethling form of lumpy skin disease comprised a granulomatous reaction in the dermis and hypodermis which extended to the surrounding tissue. During the early stages of the lesions a vasculitis and lymphangitis with concomitant thrombosis and infarction resulted in necrosis and oedema. A hallmark of the acute to subacute stages of the lesions was the presence of intracytoplasmic eosinophilic inclusions in various cell types. The inclusions consisted of the viroplasm which was identified as aggregates of electron-dense, finely granular to fibrillar deposits in which membrane-enclosed virions and occasional groups of tubular structures were observed. Various cytopathogenic changes were observed in cells exhibiting viral proliferation. The morphogenesis of the virions is discussed in relation to the cytopathogenic changes.

Flaviviruses in South Africa: diagnostic procedures.

Employing rabbit immune serum, 10 flaviviruses known to be present in South Africa could be divided into 5 serological subgroups. The subgroups conform to the general pattern described for the group. Sera from experimentally infected calves and lambs were monospecific in neutralization tests, but cross-reacted in haemagglutination inhibition tests. These results suggest that sheep and cattle sera from the field can best be tested by microneutralization tests. The greater sensitivity of embryonated hen's eggs for some viruses and of one-day-old mice for other viruses necessitates the employment of both systems for the isolation of flaviviruses from field specimens.

Flaviviruses in South Africa: pathogenicity for sheep.

Sheep are susceptible to at least 5 of the 10 flaviviruses known to be present in South Africa. Sheep, 7-9 months of age, injected with Wesselsbron, West Nile, Banzi, Uganda-S and AR 5189 (an unidentified virus related to Banzi and Uganda-S), responded with a moderate febrile reaction, a low grade viraemia of short duration and the production of virus neutralizing antibodies. The most pronounced manifestations of infection were encountered in pregnant ewes. Infection with West Nile, Banzi and AR 5189 resulted in abortion, stillbirth and neonatal death, characterized by congenital abnormalities of the brain.

Serological evidence of equine arteritis virus in donkeys in South Africa.

This paper reports the first serological evidence of exposure of donkeys to equine arteritis virus. Seven hundred and thirty-four serum samples collected between 1989 and 1992 from donkeys in different areas of South Africa were examined for the presence of antibodies against this virus by a microneutralization test. Seventeen percent of serum samples tested positive. The distribution of seropositive animals varied from none in the western Cape Province and the Transvaal Highveld to 30% in the northern Transvaal. The country-wide distribution of serologically positive donkeys suggests a longstanding presence of the virus in South Africa.

Prevalence of antibodies against some equine viruses in zebra (Zebra burchelli) in the Kruger National Park, 1991-1992.

The presence of antibodies against equine encephalosis virus (EEV) and equid herpesvirus 1 and 4 in zebra in the Kruger National Park (KNP) was demonstrated. The ability of zebra to maintain immunity against EEV is illustrated by the appearance of neutralizing antibodies in most zebra foals within months of losing their maternal immunity. This occurs in every month of the year, even in winter. The high proportion of serologically positive foals in winter is ascribed to the presence of large numbers of susceptible foals and sufficient numbers of Culicoides vectors even at that time of the year. The high prevalence of antibodies against both herpesviruses is similar to the situation in horses and suggests that herpesvirus infection is endemic among zebra in the KNP.

A simple technique for the rapid diagnosis of rabies in formalin-preserved brain.

A simple technique is described for the rapid diagnosis of rabies in formalin-preserved brain. Brain tissue was emulsified, washed with phosphate-buffered saline and digested with trypsin. The digested material was stained according to conventional immunofluorescent procedures. Digestion with trypsin markedly enhanced the staining of rabies inclusions and eliminated non-specific staining of formalin-preserved brain. The method seems to be more accurate than histological examination.

Bluetongue virus as a cause of hydranencephaly in cattle.

Hydranencephaly was produced in a foetus and a calf by intra-uterine infection with an attenuated Type 10 bluetongue virus. Laparotomy was performed on the respective dams and the foetuses, respectively 126 days and 138 days old, were inoculated intramuscularly through the uterine wall with 1 ml of a virus suspension containing 5 x 103 tissue culture infective doese. The younger feotus was aborted on Day 262, while the other one was born alive on Day 273. Both foetuses showed marked hydranencephaly.

Hydrops amnii in sheep associated with hydranencephaly and arthrogryposis with wesselsbron disease and rift valley fever viruses as aetiological agents.

During the 1974/75 lambing season numerous reports were received from various parts of the Republic of South Africa and South West Africa of severe abdominal distension in ewes after vaccination with the attenuated Rift Valley fever and/or attenuated Wesselsbron disease vaccine. The ewes were vaccinated at different stages of gestation in spite of recommendations to the contrary, the syndrome being especially obvious in ewes immunized with one or both of these vaccines during the first trimester of pregnancy. In some of the flocks hydrops amnii was recorded in as many as 15% of the ewes. Many of the ewes so affected showed a prolonged gestation of up to 6-7 months and, towards the end of gestation, were unable to rise or walk. They eventually died of ketosis, hypostatic pneumonia and complications due to dystocia. The foetuses examined were malformed and larger than normal with a mass of 3,6-6,7 kg. They usually showed arthrogryposis, brachygnathy inferior, hydranencephaly, hypoplasia or segmental aplasia of the spinal cord and neurogenic muscular atrophy. The amnion contained 8,0-18,0 1 of amniotic fluid, the endometrium was oedematous, and cystic tube-like dilatations, 1-10 mm in diameter, filled with a clear fluid, were scattered in the endometrium. No definite conclusions as to the aetiology of the syndrome could be drawn from serological tests performed on the ewes, lambs or foetuses. Preliminary experimental work confirmed previous observations that the attenuated Wesselsbron disease vaccine virus is responsible for this syndrome and that the wild-type virus is also implicated. In addition, the attenuated Rift Valley fever vaccine virus was found to the responsible for arthrogryposis and hydranencephaly without hydrops amnii and for micrencephaly and arthrogryposis associated with hydrops amnii in the ewe.

Wildebeest-derived malignant catarrhal fever: unusual epidemiology in South Africa.

The epidemiology of wildebeest-derived malignant catarrhal fever in South Africa differs from the worldwide accepted pattern. Here the occurrence of the disease is often not related to close contact between cattle and wildebeest, and most cases are observed during late winter and spring, when wildebeest calves are 8-10 months old. This is in contrast to the situation in Kenya and Tanzania, where most cases are encountered during autumn, when wildebeest calves are 3-4 months old.

Some epidemiological and economic aspects of a bluetongue-like disease in cattle in South Africa--1995/96 and 1997.

In December 1995 to March 1996 and the early summer of 1997 South Africa experienced above average rainfall which favoured the occurrence of Culicoides transmitted diseases. During this period several outbreaks of an uncommon disease of cattle occurred over a large part of the country. The clinical signs were similar to those of infection with the viruses of bluetongue (BT) and epizootic haemorrhagic disease of deer (EHD). Virus isolation from cattle and Culicoides yielded both viruses. Dual infections occurred on several farms. Typing of BT isolates yielded types 2, 3, 6 and 8. On at least two farms more than one BT virus serotype was involved. On one farm only EHD virus could be isolated from cattle and Culicoides. Serological tests confirmed that on this farm the disease was caused by EHD. In 1932/33, when a similar disease was reported conditions were vastly different. Rainfall figures show that the 1932/33 season was exceptionally dry. Techniques available at that time could not identify EHD and the cause was reported to be BT. The occurrence of BT in a dry season and over a much wider area than the distribution in South Africa of Culicoides imicola, the only proven vector for BT, is a clear indication that other species less dependent on high rainfall are involved. The present isolation of BT virus from three of five pools of parous C. bolitinos is evidence that this species, which breeds in cattle dung, may be an additional vector for BT.