Wesselsbron Virus Research Articles

Susceptibility of West African Dwarf Sheep to the Indigenous Wesselsbron Virus

SUMMARY West African Dwarf sheep infected with Wesselsbron virus developed clinical disease characterized by fever anorexia, mild leucopenia and abortion. All inoculated animals developed viraemia lasting three to four days. Haemmagglutination inhibiting and neutralizing antibodies to Wesselsbron and related flaviviruses were detected in all infected animals.

Protein-calorie malnutrition impairs the anti-viral function of macrophages.

SummaryMice which are normally resistant to infection with Wesselsbron (WBV) virus became rapidly susceptible to disease due to this agent after being placed on protein-depletion diet. After ip inoculation large amounts of virus appeared in the circulation followed by fatal encephalitis. In normally fed mice only small amounts of virus could be detected in blood and no disease developed. This suggested that local defense mechanisms which normally restrict the extent of infection was sensitive to the early effects of protein-calorie malnutrition. That this was due at least in part to impaired antiviral function of macrophage under these conditions was confirmed by in vitro macrophage studies. Over the course of 24 hr infectious WBV disappeared after inoculation into cultures of normal macrophages whereas infectivity persisted at high titers in macrophages from protein-depleted mice.This work was supported by a grant from the Rockefeller Foundation.

Role of macrophages in Wesselsbron and Germiston virus infections of mice.

Mice develop age-dependent resistance to intraperitoneal infection with Wesselsbron virus, but not with Germiston virus. This resistance correlates with the capacity of peritoneal macrophages from older mice rapidly inacativated the infectivity of Wesselsbron virus, whereas Germiston virus replicated in these cells. Peritoneal macrophages from older mice protected cell cultures against Wesselsbron virus infection, but macrophages from newborn mice did not. Electron microscopic observations suggested that Wesselsbron virus was actively phagocytosed by macrophages, whereas Germiston virus entered the cells by other means and thus, presumably, circumvented the normal killing mechanisms of these cells. Germiston virus may also have directly impaired these killing functions, however, in that the ability of macrophages to kill phagocytosed Diplococcus pneumonaie was significantly less after macrophages were exposed to the virus.

Factors influencing the vector potential of Aedes aegypti and Culex quinquefasciatus for Wesselsbron virus.

The threshold of infection with Wesselsbron virus was lower for Aedes aegypti than for Culex quinquefasciatus , but after ingesting higher doses of virus, C. quinquefasciatus more frequently became infected. Nevertheless, once infection was initiated in A. aegypti , the virus replicated to a high titer in a greater proportion of mosquitoes. The net result was that A. aegypti , after ingesting small amounts of virus, transmitted virus more efficiently and after a shorter extrinsic incubation period than C. quinquefasciatus ; after the ingestion of high doses, both species transmitted infection with equal efficiency.

Further isolations of the arboviruses from mosquitoes collected in Tongaland, South Africa, 1960-1968.

Over a period of 8.5 years 168,231 mosquitoes, including at least 52 species, were collected in a Game Reserve and tested for infection with arboviruses. Fifty-two isolations, including strains of Sindbis, Middelburg, Ndumu, Wesselsbron, Spondweni, Bunyamwera, Shokwe, Germiston, Pongola, Mossuril, Lebombo, Ingwavuma and Simbu viruses were made from 5 species of mosquito. The most frequently infected species, Aedes (Neomelaniconion) circumluteolus (Theobald), yielded 37 strains which included strains of 11 arboviruses. The appearance of particular viruses was intermittent and it was not possible to incriminate any single species fundamentally in the survival of these viruses. Seven species comprised 96% of the total number of mosquitoes tested and it seemed possible that unidentified vectors may be among species collected in small numbers.

Physical changes of Wesselsbron virus occurring during attenuation in foetal lamb kidney cells.

Two strains of Wesselsbron virus, one having undergone 12, the other 110 (attenuated strain) passages in foetal lamb kidney (FLK) cells were examined by means of a number of physical techniques.

Formation of Wesselsbron virus in BHK-21 cells.

The multiplication of attenuated and virulent strains of Wesselsbron virus in BHK-21 cells have been investigated electron microscopically. In thin sections of cells infected with virulent virus and harvested at different time intervals, mesh-like structures, similar to those reported by previous workers, are observed. However, cells infected with the attenuated form of the virus do not show these structures at all, indicating that these mesh-like bodies are not a prerequisite for virus production. Cytoplasmic inclusions containing dense nucleoids and developing virus particles are reported. Mature virus particles are commonly found in cisternae of the endoplasmic reticulum in both virulent and attenuated forms of the virus. Particle measurements have yielded a diameter of 45 mμ, which is somewhat larger than measurements obtained by previous workers. The similarity between the mesh-like structures reported in this work, the “granular virus-forming areas” reported bySoutham et al. (1964) in HBp2 cells infected with West Nile virus and the structures occurring in cells infected with yellow fever virus (Bekgold andWeibbl, 1962) may indicate a close cytopathic relationship between these group B arboviruses.

Assay of arbovirus neutralizing antibody by micro methods

Efficient, reproducible and specific neutralizing antibody assays are needed, particularly for use in arboviral studies in areas where antigenic cross reactions make serological interpretation difficult. Accordingly, 2 methods were developed for this purpose. A micrometabolic inhibition (MMI) test with BHK-21 cells in disposable “U”-bottomed microtitre plates was used with Japanese encephalitis, Wesselsbron, Sindbis, chikungunya and Batai viruses. The MMI test was highly specific, of efficiency comparable with the haemagglutination-inhibition (HI) test, and was very sparing of reagents and sera. Although equal to or better in sensitivity than conventional cell culture neutralization tests, it was not as sensitive as HI or plaque-reduction neutralization (PRN) tests. The LLC-MK2 cell microculture PRN test was devised for use with the dengue viruses or for use when a combination of precision of antibody measurement and efficiency of testing was required. The microculture and 1 oz. bottle culture PRN tests were of equal specificity. Although not as precise as the bottle PRN test, the microculture PRN test is suitable for routine serology and has the added advantages that it is more efficient and requires less serum and reagents.

Intracytoplasmic inclusions in foetal lamb kidney cells infected with Wesselsbron virus

An electron microscopic study of the intra-cellular development of Wesselsbron virus, a group B Arbovirus, has been undertaken. Secondary cultures of foetal lamb kidney cells infected with Wesselsbron virus were harvested at daily intervals, fixed in 1 ~ osmium tetroxide, dehydrated and embedded in methacrylatc. Ultrathin sections were stained with lead citrate and examined in a Siemens Elmiskop I electron microscope. In control uninfected cultures of foetal lamb kidney cells the intracellular organe]les were clearly identified and regular in appearance. Nuclear chromatin was evenly distributed and the cytoplasm not vacuolated. Infected cells did not show any distinct change until 48 hours after infection, when the nuclei appeared closely packed and displayed a margination of their chromatin. The most striking observation was the appearance of many unusual orderly-patterned inclusions in "crystalline-like" array, in the cytoplasm of the cells. The regularity and the apparent three dimensional nature of these inclusions is illustrated in Fig. 1. They appeared to be closely associated with the endoplasmic reticulum which showed gross vesiculation in the vicinity of the arrays. The varying organization within the inclusions is clearly presented in Fig. 2. Sections through different planes show areas of hexagonal units in "honey-comb" formation (A) and four-sided units in reticulate array (B). This may suggest an arrangement of short hexagonal cy]inders

Survey for antibodies against arthropod-borne viruses in the sera of indigenous residents of the caprivi strip and bechuanaland protectorate

Sera collected in 1959 from 602 residents of 19 localities in the Caprivi Strip and Bechuanaland Protectorate were tested for HI antibodies against 15 viruses—4 from Group A, 7 from Group B, 1 from Group C, 2 from the Bunyamwera Group, and Rift Valley fever virus. Results of these tests were largely negative for the 5 localities in the Kalahari Desert, but indicated a great deal of virus activity in the Caprivi Strip and the Okavango Basin. Sera positive in the HI test were further tested with the respective viruses by the mouse neutralization test. Selected sera were also tested for neutralizing antibodies against 4 other ungrouped viruses. Neutralization test results gave further evidence of activity of a wide spectrum of viruses, but showed that immunity levels were highest with Sindbis, West Nile, Wesselsbron, Bunyamwera and Germiston viruses. The results of yellow fever neutralization tests with sera collected in the Okavango Basin during 2 previous surveys are reviewed. The present survey offers no conclusive evidence that this virus has been active among the population sampled.

Survey for antibodies against arthropod-borne viruses in the sera of indigenous residents of Angola

Sera collected in 1960 from 492 indigenous residents of 14 widely scattered localities in Angola were tested for HI antibodies against 18 viruses: 5 from Group A, 9 from Group B, 1 from Group C, 2 from the Bunyamwera Group, and Rift Valley fever virus. Results of these tests indicated that the prevalence of antibodies was greatest in the 6 localities sampled in the north-western coastal and plateau region. Sera positive in the HI test were further tested with the respective viruses by mouse neutralization test. Analysis of these results according to sera positive for only one virus of Group A, B or Bunyamwera indicated that Sindbis, chikungunya, Semliki Forest, Wesselsbron, Zika, H 336, West Nile, Bunyamwera and Germiston viruses have been active, predominantly in the north-western region, and that Spondweni virus has been present. There was no evidence that Mayaro or Middelburg virus has infected the population sampled, or that Ntaya, dengue 1 or dengue 2 virus has been present. In 3 localities in the north-west interpretation of results with Group B viruses was complicated by the fact that some of the donors had been vaccinated against yellow fever. HI test results with Oriboca virus suggest that this or a closely related member of Group C exists in Angola. In additional neutralization tests, one or more sera from children and adults in each of the 6 north-western localities protected against Lumbo (California complex), Pongola or Bwamba fever virus.

Susceptibility of some African wild rodents to infection with various arthropod-borne viruses

The susceptibility, measured in terms of viraemia and antibody response, of nine species of African wild rodents to one or more of 11 different arthropod-borne viruses was investigated. None of the rodents was susceptible to Spondweni, Pongola and Wesselsbron viruses. Following inoculation with West Nile and Bunyamwera viruses a single rodent species showed low grade viraemia. One or more rodent species responded with viraemia to Simbu, Rift Valley fever, Uganda S, Germiston, chikungunya and Middelburg viruses. Forty-six of 72 convalescent sera from rodents which developed viraemia had antibody. The possibility of these rodents being implicated in transmission cycles of these viruses is discussed.