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Summary 1. Studies on Sindbis virus, a newly recognized member of the arthropod-transmitted viruses, are described; these include data on its immunological characteristics, distribution in the Nile Valley, vertebrate host range, and transmissibility by arthropods. 2. The virus has been isolated from mosquitoes during three successive summers, and once from a juvenile hooded crow (Corvus corone sardonius). 3. It has been placed by Casals and Brown (1954) in Group A of the arthropod-transmitted viruses, but is distinguishable from other members of this group by the neutralization test. 4. Its particle size, estimated by gradacol membrane filtration, is between 40 and 48 mu. 5. On initial passages by brain-to-brain transfer it is fatal to infant mice but not to adult mice. 6. It is highly fatal to embryonated hens' eggs and is markedly cytopathogenic to outgrowths of fibroblastic cells in chick embryo tissue cultures. 7. Experimentally it is easily transmitted by Culex mosquitoes (Culex pipiens L. and Culex univittatus Theobald), and Ornithodoros savignyi (Audouin) ticks are infectible by parenteral puncture and will subsequently transmit the infection by feeding upon infant mice. 8. Antibody surveys imply a) a wide vertebrate host range including man, domestic quadrupeds, birds, and domestic fowl, and b) frequent human infection (27 per cent), particularly in the age group of 15 years and over (34 per cent), in the Nile Delta, and less frequent human infection (12 per cent) in the Southern Sudan. 9. No information is available on the symptomatology of natural infections.

Summary St. Louis encephalitis virus was isolated on 23 occasions from mosquitoes collected between September 7 and October 25 at widely separated localities of the four-county Tampa Bay area during the St. Louis encephalitis epidemic of 1962. Twenty-two of these isolations were obtained from 485 pools of Culex nigripalpus; the 23rd was from 91 pools of Melanoconion, a subgenus of Culex. The mosquitoes were collected alive in battery-powered light traps and traps baited with ducklings or chicks. These isolations indicate that infected vectors were prevalent over a vast area exposing the human population to infection throughout the region.

Summary Isolations are reported of three arboviruses designated as Quaranfil, Chenuda, and Nyamanini in the Nile Delta of Egypt. Quaranfil virus was isolated from Argas Persicargas arboreus, Argas (Argas) reflexus hermanni, nestling cattle egrets (Bubulcus ibis ibis), and a pigeon squab, and from the blood of two children during a febrile illness. The ecological characteristics of this virus deduced from virus isolation from naturally infected vertebrates and arthropods, limited surveys for antibodies, and experimental infection and transmission, suggest that it is essentially a bird virus, transmitted by Argas ticks. The two species of birds, the cattle egret and the pigeon, that were definitely incriminated, nested in colonies that were heavily parasitized by Argas ticks—the former by A. arboreus and the latter by A. r. hermanni. Apparently, infection is acquired mainly by the young birds from the infected ticks, and the birds in turn infect additional larval and nymphal ticks. Though the virus survived through moltings of the ticks, transovarian passage was not demonstrated. Evidence is presented for the occasional tangential infection of associated human populations. Chenuda virus was isolated from A. r. hermanni collected in two large pigeon houses, and presumably the pigeon is the vertebrate host. The low pathogenicity of this virus curtailed supporting experimental evidence on infection and transmission. Two strains of Nyamanini virus were isolated from A. arboreus and one strain from a nestling egret collected at a large rookery where Quaranfil virus was also isolated.

Summary and Conclusions The results are recorded of an investigation of the geographical distribution of West Nile virus in Egypt and the southern Sudan, the epidemiology of human infection, and the general ecology of the virus in the Nile Delta, as revealed by virus isolations, surveys for specific antibodies and study of the biological environment. According to serological surveys the virus is widely disseminated along the Egyptian Nile and in the southern Sudan; 61 per cent of 1168 human bloods collected in Egypt and 40 per cent of 350 collected in the Sudan neutralized WN virus. In an endemic area in the Nile Delta where the intensive studies were conducted, West Nile infection is essentially a childhood disease with yearly peaks of transmission during mid-summer. No reliable information on the symptomatology of the infection in children was obtained, but the impression was gained that it is a self-limited, non-fatal febrile disease rarely associated with definite manifestations of encephalitis. The virus was repeatedly isolated from the blood of febrile children (23) and from mosquitoes, Culex univittatus (12) and Culex antennatus (5), twice from pigeons (Columba livia) and once from the hooded crow (Corvus corone sardonius). The fact that C. univittatus was more frequently found to be infected than any other species of mosquito may be due to its relative predilection for avian blood. None of 530 pools of other arthropods, including ticks, lice, fleas, mites and flies, yielded virus. On both experimental and ecological grounds it is concluded that the main cycle of the virus is probably through mosquitoes and birds in which man may become involved. Serological evidence points to infections of domestic quadrupeds, but these are probably only tangential or dead-end infections. It is likely that non-migratory birds are responsible for the local dissemination of the virus but, as it appears to be endemic in parts of the Nile Delta, its transport over long distances by migratory birds was not investigated. There is evidence for believing that the virus over-winters through a process of retarded transmission by the mosquitoes that remain active throughout the colder months, although the possible role of ticks as a reservoir of the virus should be further investigated. Non-endemicity in the northern rim of the Delta may be accounted for by the less dense human and bird population there and the scarcity of what appears to be the most important vector, C. univittatus.

An epidemic of St. Louis encephalitis occurred during the summer and fall of 1964 in McLeansboro, a rural village of Hamilton County in southern Illinois. Attending physicians clinically diagnosed 22 cases, including 2 deaths, as encephalitis. Serologic evidence of SLE infection was obtained in more than half of the cases. In a survey to determine the prevalence of inapparent infection among residents, 32 of 615 donors had both HI and CF St. Louis virus antibodies in their sera. Over half of the mosquito pools, each containing approximately 25 Culex pipiens complex mosquitoes, yielded SLE virus. Altogether, there were 40 such positive pools. Tests to determine the identity of riiosquito bloodmeals indicated that the majority had fed on birds. Tissues from 3 house sparrows, a chimney swift and a catbird yielded strains of SLE virus. Surveillance for arbovirus activity in McLeansboro has continued since the 1964 outbreak.

A serological survey of the Seminole Indians in south Florida for evidence of exposure to arbovirus infection indicated not only past infection with the recognized North American encephalitis viruses-a high incidence for St. Louis encephalitis-but exposure to a Bunyamwera group agent and to Venezuelan equine encephalitis virus, activity of which had not been previously recognized north of Panama.

Venezuelan equine encephalitis virus was isolated three times from the Culex (Melanoconion) species of mosquitoes collected in south Florida in June, July, and October, 1963. Specific antibody was present in 16 of 28 Peromyscus gossypinus (cotton mice) and 3 of 16 Sigmodon hispidus (cotton rats) sampled from one of the infected sites in January 1964.

The terms kwashiorkor, marasmus, defective cellular immunity, and famine are exotic terms to most Americans, but they have foreboding implications for both present and future American medi...

SummaryThe adaptation of 2 strains of West Nile virus, of Tamil Nad virus and of Japanese B encephalitis virus to chick embryo cell and monkey kidney cell cultures is described. After a variable nu...

Summary1. Strains of West Nile virus were isolated from the blood of two pigeons, Columba livia, and one hooded crow, Corvus corone sardonius, in an endemic area of the Nile Delta of Egypt in July and August 1953. The virus was also obtained from the brain and spleen of one of the pigeons. 2. The relation of these isolations to the environment is briefly discussed.