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: 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 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 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.

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.

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.

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.

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.

Ebola and Marburg viruses: I. Some ultrastructural differences between strains when grown in Vero cells.

A strain of Marburg virus and two strains of Ebola virus grown in Vero cells were compared by electron microscopy. The outer coat of the Marburg virion appeared to be more resistant to erosion by negative staining techniques than that of the Epbola strains. Marburg virus commonly produced "torus" forms and short filaments; the Zaire strain of Ebola produced extensive branched forms and very long filaments; the Sudan strain of Ebola produced shorter, less branched structures but very many aberrant forms. The mechanism for the production of these aberrant forms is described.

Haematological and biochemical monitoring of Ebola infection in rhesus monkeys: implications for patient management.

Patients with severe viral infections such as Lassa or Ebola may be denied adequate laboratory investigations because of justifiable fears among laboratory staff. This study in monkeys was designed to provide comprehensive haematological and biochemical monitoring in a contained environment during all stages of Ebola infection. Marked neutrophilia, depletion of lymphocytes, and early failure of platelet aggregation preceded a consumption coagulopathy with a microangiopathic haemolytic anaemia, thrombocytopenia, and failure of prostacyclin production by vascular endothelium. Liver dysfunction was moderate but in conjunction with the dehydration and hypoalbuminaemia could be expected to precipitate renal failure and shock. It seems reasonable to anticipate successful patient support with a patient management isolator and treatment with platelet transfusions, fresh frozen plasma, and possibly prostacyclin when haemostasis is defective during this otherwise self-limiting illness.

Congo/Crimean haemorrhagic fever virus from Iraq 1979: I. Morphology in BHK21 cells.

Congo-Crimean Haemorrhagic Fever virus, isolated from a patient in Iraq, was grown, after passage in suckling mouse brain, in BHK cells. The particles matured after 8-9 days in these cells by budding, usually singly, into cytoplasmic vacuoles throughout the host cells. The virions had an overall diameter of 115 to 125 nm, including rounded surface spikes 15 nm long and 10 nm wide. The viral cores, surrounded by a lipid unit membrane, contained discrete electron-dense elements. It is suggested that the spikes, dimpled at their outer end and possibly hollow throughout their length, passed out through "pores" in the unit membrane.

Congo/Crimean haemorrhagic fever in Dubai. An outbreak at the Rashid Hospital.

A hospital outbreak of haemorrhagic fever took place in Dubai in November, 1979. The index case died in the casualty department shortly after admission. There were five secondary cases among hospital staff, two of whom died. When, 3 months after this outbreak, a patient with symptoms characteristic of haemorrhagic fever was admitted, immediate barrier nursing prevented further secondary cases.

Ebola and Marburg viruses: II. Thier development within Vero cells and the extra-cellular formation of branched and torus forms.

The development of Marburg virus and the Sudanese and Zaire strains of Ebola virus in Vero cells as visualized by electron microscopy is described. Despite differences in timing, all three strains appear to pass through identical stages of development. Initially there is a large increase in nucleolus material, and viral precursor material arranges itself in spirals and then into tubes. The cells fill with core material, which passes to the plasmalemma, which often proliferates. Each virion passes through the plasmalemma, acquiring a coat of host material. The formation of torus forms is discussed; the branched appearance that is often seen is believed to be an aberrant form. The reasons for this view are put forward.

Arbovirus infections in Sarawak, October 1968--February 1970 Tembusu and Sindbis virus isolations from mosquitoes.

Thirty isolations of Tembusu virus and four of Sindbis virus were obtained from approximately 280 000 mosquitoes collected between October 1968 and February 1970 in Sarawak, particularly from K. Tijirak, a Land Dyak village 19 miles South of Kuching. Twenty-two isolations of Tembusu virus and two of Sindbis virus were from Culex tritaeniorhynchus; two of Tembusu virus and two of Sindbis virus came from Culex gelidus. Tembusu virus was active throughout the year at K. Tijirak, the highest infection rates in C. tritaeniorhynchus being in January-March and May-August, when the C. tritaeniorhynchus population was declining and ageing. These results confirm that C. tritaeniorhynchus is the principal arthopod host of Tembusu virus in Sarawak. Antibody studies suggest that birds, particularly domestic fowl, are probably vertebrate maintenance hosts of Tembusu and Sindbis viruses in Sarawak.

Pathophysiology of shock and hemorrhage in a fulminating viral infection (Ebola).

Eleven rhesus monkeys were monitored intensively during experimental infection with Ebola virus. Prominent neutrophilia with left shift and lymphopenia were the earliest abnormalities and were statistically significant by day 4 (P less than .02 and P less than .01, respectively). By day 4 falls in platelet counts were not statistically significant, whereas in vitro platelet aggregation was markedly depressed, progressing rapidly to complete failure by the time of maximum illness. Intraplatelet protein studies suggested this event was the result of in vivo activation and degranulation. Coagulation cascade defects were mainly in the intrinsic system and were surprisingly mild, with no evidence of selective consumption or production deficit of factor VII or VIII. When the possibility of indirectly mediated damage to endothelium possibly by a nonspecific immune response was examined, weight loss was less severe in drug-treated monkeys, and all had detectable plasma prostacyclin metabolites, but there was no improvement in survival.