Ultrastructure of Ebola virus particles in human liver.

Electron microscopy of tissues from two necropsies carried out in the Sudan on patients with Ebola virus infection identified virus particles in lung and spleen, but the main concentrations of Ebola particles were seen in liver sections. Viral precursor proteins and cores were found in functional liver cells, often aligned in membrane-bound aggregations. Complete virions, usually found only extracellularly, were mainly seen as long tubular forms, some without cores. Many tubular forms had 'enlarged heads' or 'spores' and some branched and torus forms were identified. The size and structure of the Ebola virus forms appear to be virtually indistinguishable from those of Marburg virus.

Yellow fever in the Gambia, 1978--1979: epidemiologic aspects with observations on the occurrence of orungo virus infections.

An epidemic of yellow fever (YF) occurred in the Gambia between May 1978 and January 1979. Retrospective case-finding methods and active surveillance led to the identification of 271 clinically suspected cases. A confirmatory or presumptive laboratory diagnosis was established in 94 cases. The earliest serologically documented case occurred in June 1978, at the extreme east of the Gambia. Small numbers of cases occurred in August and September. The epidemic peaked in October, and cases continued to occur at a diminishing rate through January, when a mass vaccination campaign was completed. The outbreak was largely confined to the eastern half of the country (MacCarthy Island and Upper River Divisions). In nine survey villages in this area (total population 1,531) the attack rate was 2.6--4.4%, with a mortality rate of 0.8%, and a case fatality rate of 19.4%. If these villages are representative of the total affected region, there may have been as many as 8,400 cases and 1,600 deaths during the outbreak. The disease incidence was highest in the 0- to 9-year age group (6.7%) and decreased with advancing age to 1.7% in persons over 40 years. Overall, 32.6% of survey village inhabitants had YF complement-fixing (CF) antibodies. The prevalence of antibody patterns indicating primary YF infection decreased with age, in concert with disease incidence. The overall inapparent:apparent infection ratio was 12:1. In persons with serological responses indicating flaviviral superinfection, the inapparent:apparent infection ratio was 10 times higher than in persons with primary YF infection. Sylvatic vectors of YF virus, principally Aedes furcifer-taylori and Ae. luteocephalus are believed to have been responsible for transmission, at least at the beginning of the outbreak. Eighty-four percent of wild monkeys shot in January 1979 had YF neutralizing antibodies, and 32% had CF antibodies. Domestic Aedes aegypti were absent or present at very low indices in many severely affected villages (see companion paper). In January, however, aegypti-borne YF 2.5 months into the dry season was documented by isolation of YF virus from a sick man and from this vector species in the absence of sylvatic vectors. Thus, in villages where the classical urban vector was abundant, interhuman transmission by Ae. aegypti occurred and continued into the dry season. A mass vaccination campaign, begun in December, was completed on 25 January, with over 95% coverage of the Gambian population. A seroconversion rate of 93% was determined in a group of vaccinees. This outbreak emphasizes the continuing public health importance of YF in West Africa and points out the need for inclusion of 17D YF vaccination in future programs of multiple immunication.

A method for increasing the surface details of resin embedded viruses using Congo/Crimean haemorrhagic fever virus as a model.

The surface details of resin embedded viruses can be greatly enhanced by the use of uranyl acetate block staining. The virions are embedded in agar immediately after fixation and block stained with 3% uranyl acetate in methanol during dehydration. This technique allows those particles outside their host cells to show clearly the spikes normally seen only by the separate use of negative staining.

The susceptibility of Culicoides variipennis Coq. (Diptera: Ceratopogonidae) to laboratory infection with Rift Valley fever virus.

The vector potential of Culicoides variipennis for Rift Valley fever virus (RVFV) was investigated. Insects from a colony maintained at the Animal Virus Research Institute, Pirbright, were fed through a membrane on a mixture of mouse blood and RVFV (virus concentration of blood meal 7 X 95 log10 MLD50ml). Engorged insects were maintained at 25 degrees C +/- 1 degrees C. Samples of insects were tested at daily intervals to determine their virus content. Four of the five females tested immediately after feeding contained virus. The mean virus concentration of these infected flies was 2 X 7 log10MLD50. The virus concentration per fly decreased to 0 by day 2 post infection. On day 3, a virus concentration of 2 X 4 log10 MLD50 per fly was recorded from a pool of 17 flies but between day 4 and day 12 when the experiment terminated no virus was detected in any of the 135 females tested. Because of the pathogenic nature of RVFV, this work was carried out under the stringent security regulations at the PHLS Centre for Applied Microbiology and Research, Porton Down. The problems arising from experiments requiring the handling and infection of insects under such conditions are described.

Ebola haemorrhagic fever: experimental infection of monkeys.

Experimental infection of rhesus and vervet monkeys with Ebola virus produced a uniformly fatal illness. The course of the disease resembled that found in man with weight loss, anorexia, fever, haemorrhages and skin rash being frequently seen. Viraemia was obvious within two days of infection and persisted until death which occurred between days five and eight. Virus was found in high concentrations in several organs but particularly in the liver, spleen, and lungs.

Arbovirus infections in Sarawak, October 1968-February 1970: GETAH virus isolations from mosquitoes.

14 strains of Getah virus were isolated from a variety of mosquito species collected in Sarawak between October 1968 and February 1970. Ten strains were isolated from C. tritaeniorhynchus 7 of them at K. Tijirak. Single strains were isolated from C. gelidus, C. pseudovishnui, M. bonneae/dives and Aanopheles species. 6 of the isolates were obtained in October 1968 when Japanese encephalitis, Tembusu and Sindbis viruses were also very active. The available evidence suggest that Getah virus in Sarawak is maintained in a cycle similar to that of Japanese encephalitis virus and involves C. tritaeniorhynchus, C. gelidus and domestic pigs.

Arbovirus infections in Sarawak, October 1968-February 1970: human serological studies in a land Dyak village.

449 human sera collected in a Land Dyak village were tested for antibodies to 11 arboviruses. Japanese encephalitis and dengue virus antibodies were particularly prevalent. The rates of infection with these viruses were estimated to be 5-2% per annum for Japanese encephalitis, 8-8% for dengue 1 and 4-3% for dengue 2. Chikungunya virus antibodies were quite common with an annual infection rate of the order of 5% per annum. Infections with other Group A and B and Bunyamwera group viruses were generally at a low level.

Arbovirus isolations from, and serological studies on, wild and domestic vertebrates from Kano Plain, Kenya.

Arbovirus infection and presence of haemagglutination-inhibiting antibodies in small mammals, birds and livestock were examined over a period of five years on the Kano Plain in western Kenya. Eleven isolations were made from mammals and birds. The viruses were identified as Arumowot and Germiston while three different agents could not be shown to be related to 188 African arboviruses. Prevalence of antibodies against arboviruses suspected of occurring in the area was generally low.

Arbovirus infections in Sarawak: the role of the domestic pig.

The possible role of pigs as arbovirus maintenance hosts and their importance as amplifier hosts was studied. Blood samples from 464 pigs of all ages collected in 1962 and 1964 were tested against 10 arboviruses. Antibodies to Japanese encephalitis and Getah viruses were particularly prevalent and their calculated monthly infection rates were 19-5% and 13-3% respectively. In 1969, 447 pigs were bled monthly throughout the year and the infection rates for Japanese encephalitis virus were calculated in pigs during the first year of life. Infection rates were not uniform throughout the year; the rate increases as the pig grew older and there was a marked seasonal increase in the infection rate in the period from November to January. This coincided with the seasonal major population peak of Culex tritaeniorhynchus following intense breeding of this mosquito prior to rice planting. It is suggested that, in Sarawak, the pig acts as a maintenance host of Japanese encephalitis in a cycle involving C. gelidus mosquitoes and also acts as an important amplifier host towards the end of the year in a cycle involving C. tritaeniorhynchus. It is further suggested that Getah virus is maintained in a similar cycle between C. tritaeniorhynchus and pigs.

Arbovirus isolations from mosquitoes: Kano Plain, Kenya.

Arbovirus isolation attempts on 324,486 mosquitoes captured over a four-year period on the Kano Plain, Kenya, yielded 15 isolates including Pongola (six strains), Ilesha (three strains), Germiston (two strains), Sindbis (one strain), Barur (one strain) and two viruses which could not be characterized. Mansonia uniformis, Anopheles gambiae and Culex antennatus constituted 70% of the total collection and accounted for all of the isolates except one, which came from Anopheles funestus.

Comparative studies of some African arboviruses in cell culture and in mice.

Twenty African arboviruses, five alphaviruses, nine flaviviruses, three Bunyamwera Group viruses, two Bwamba Group viruses and one ungrouped virus were titrated in parallel in 11 cell systems in suckling mice and adult mice. The relative sensitivities of the in vitro and in vivo systems have been compared. The highest infectivities were obtained in suckling mice. Vero and LLC-MK2 cells produced plaques with the greatest number of viruses and Semliki Forest virus grew most readily. Ntaya virus and Dengue 1 virus were difficult to culture in vitro and Zika virus yielded better in cell culture than in adult or suckling mice. In vitro and in vivo neutralization tests were made on human sera in groups of 50. Each group of sera was tested against one of five viruses, representative of three of the arbovirus groups titrated. Good agreement was obtained between the two test systems with West Nile, O'nyong-nyong and Wesselsbron viruses but there were significant differences in results obtained with Germiston and Pongola viruses.

Enhanced resistance of mice to infection with Langat (TP21) virus following pre-treatment with Sindbis or Semliki forest virus.

Significant protection to heterologous i.c. challenge with the flavovirus Langat occurred after a single i.c. injection of avirulent strains of the alpha viruses Semliki Forest or Sindbis given 1 day to 5 weeks before challenge. Some protection also occurred after an i.p. infection with these viruses. We consider that the protection afforded by the alpha viruses is due to interference with the multiplication of Langat virus and is related to the maximum level of brain infectivity reached in the alpha virus infection.

Viral infections in travellers from tropical Africa.

Examination of sera from 86 travellers to Britain from tropical Africa disclosed evidence of past infection with 10 identifiable viruses, of which the most important were O'nyong-nyong, dengue, chikungunya, and Ntaya. The findings indicate that infection with O'nyong-nyong may be acquired sporadically in Nigeria, Ghana, and Sierra Leone, where it has not previously been identified. Chikungunya infection had not been recorded in West Africa other than Nigeria and Senegal. Patients from Sierra Leone and contiguous Liberia had antibodies to this infection. An outbread of dengue fever in the Seychelles in early 1977 was confirmed. Ntaya virus, though known in Uganda, Cameroon, and Zaire, appears also to be transmitted in Kenya, Nigeria, and Zambia. Clinical studies indicated that chikungunya infection may present with alimentary features, possibly with jaundice. The clinical features of Ntaya infection may include kizarre neurological manifestations in addition to fever. The absence of Lassa antibodies among these travellers suggested that this infection is not a common hazard among such persons.

A case of Ebola virus infection.

In November 1976 an investigator at the Microbiological Research Establishment accidentally inoculated himself while processing material from patients in Africa who had been suffering from a haemorrhagic fever of unknown cause. He developed an illness closely resembling Marburg disease, and a virus was isolated from his blood that resembled Marburg virus but was distinct serologically. The course of the illness was mild and may have been modified by treatment with human interferon and convalescent serum. Convalescence was protracted; there was evidence of bone-marrow depression and virus was excreted in low titre for some weeks. Recovery was complete. Infection was contained by barrier-nursing techniques using a negative-pressure plastic isolator and infection did not spread to attendant staff or to the community.

A comparative study of strains of Ebola virus isolated from southern Sudan and northern Zaire in 1976.

During the 1976 Ebola virus outbreak in Sudan, the investigations team gained the impression that fewer haemorrhagic manifestations and few fatalities occurred during the later stages of the epidemic after the virus had undergone several generations in man. This impression was also noted in guinea pigs experimentally infected with Sudanese and Zairean strains of Ebola virus. The virulence of the Sudanese isolates was less intense than isolates emanating from Zaire. Similar findings were seen in monkeys; a Zairean isolated produced fatal infections, whereas monkeys inoculated with a Sudan strain generally recovered. Two monkeys, which had recovered from Sudanese strain infections and had developed high levels of antibody detectable by immunofluorescence, were challenged with the Zairean strain. Both developed viraemias and died. The mechanisms of this "failed protection" are discussed.

Ebola virus: a comparison, at ultrastructural level, of the behaviour of the Sudan and Zaire strains in monkeys.

Histopathological and electron microscopical examination of human liver specimens collected during the Ebola haemorrhagic fever outbreaks in Zaire and Sudan indicated that Zairean strains of the virus produced more extensive lesions. Experimental infection of rhesus monkeys wiht Zairean and Sudanese strains of Ebola virus produced similar changes to those found in man. In Zairean strain infections large numbers of virus particles were found in the liver, lung and spleen accompanied by extensive necrosis in the spleen. In Sudan strain infections particles were found only in the liver and in greatly reduced numbers. The main distinction lay in the high proportion of aberrant particles found with the Sudanese strain. The possibility of these being defective particles is discussed.

The pathology of experimental Ebola virus infection in monkeys.

Six rhesus and two vervet monkeys were infected intraperitoneally with Ebola virus. They developed an acute haemorrhagic fever with skin rash 4 days later and died 6--12 days after infection. Histopathological lesions of acute necrosis were present in the liver, spleen, lymph nodes, lungs and testes. The presence of fibrin thrombi in several organs was suggestive of the occurrence of disseminated intravascular coagulation during the infection.