Charles H. Calisher

Yellow fever vaccination and pregnancy: a four-year prospective study

During an outbreak of yellow fever (YF) in Nigeria in 1986-1987, women at various stages of pregnancy were vaccinated against YF, either because those pregnancies were not known at the time or because they requested vaccination out of fear of acquiring the disease. This offered an opportunity to assess the safety and efficacy of YF vaccine in pregnant women and the effect of this vaccine on their newborn children. Pre-vaccination and post-vaccination serum samples from the vaccinated pregnant women were tested by enzyme-linked immunosorbent assay and by neutralization tests for antibody to YF virus. The results showed that the antibody responses of these pregnant women were much lower than those of YF-vaccinated, non-pregnant women in a comparable control group. Follow-up of these women and their newborn children for 3-4 years showed no abnormal effect that could be attributed to the YF vaccine, which suggests that vaccination of pregnant women, particularly during a YF epidemic, may not be contraindicated.

Ross River virus (Togaviridae: Alphavirus) infection (epidemic polyarthritis) in American Samoa

An outbreak of Ross River virus infection (epidemic polyarthritis), which occurred in American Samoa between August 1979 and January 1980, is described. On the basis of a serological survey performed near the end of the epidemic, it is estimated that at least 13,500 people were infected. Ross River virus was isolated from the blood of a single polyarthritis patient. Plaque reduction neutralization tests, using this virus strain, were done on 393 human and 143 animal sera collected on Tutuila island. Over-all, 43.8% of the people sampled had evidence of infection. Sera from 100 adult residents of the same island, collected in 1972, had no Ross River antibody, suggesting recent introduction of the virus. In contrast to the human serological data, the prevalence of Ross River antibodies among animals was relatively low. Dogs and pigs had the highest rates with 20% and 15%, respectively. Results of this study suggest that the Ross River virus cycle during the epidemic in American Samoa involved primarily humans and mosquitoes with animals less frequently infected. These observations plus the recent introduction of Ross River virus into new areas of the South Pacific suggest that a major change has occurred in the epidemiology of epidemic polyarthritis.

Sindbis virus isolations from Saudi Arabian mosquitoes

A study in late 1979 to early 1980 was conducted to assess arbovirus activity in the Eastern Province of Saudi Arabia. From 38,245 mosquitoes collected at 3 locations, 16 isolations of Sindbis virus were made: 13 from Culex univittatus and one each from Cx tritaeniorhynchus, Cx pipiens complex, and Culex spp. These isolations represent the first records of a mosquito-borne virus from the Gulf of Arabia and implicate Cx univittatus as the principal vector. A potential risk of human diseases exists due to Sindbis virus in Saudi Arabia.

Isolations of cache valley virus in Texas, 1981

Two strains of the same virus (isolates AR 168 and 7856), were isolated in 1981 from an apparently healthy cow and a sick sheep in TX, U.S.A. These isolates were shown to be members of the Bunyamwera serogroup (family Bunyaviridae, genus Bunyavirus) by complement-fixation tests. Serum dilution-plaque reduction neutralization test results indicated that the isolates are closely related to Cache Valley virus. The virus isolates were characterized by sensitivity to lipid solvent, size (50-100 nm by filtration and 70 nm by electron microscopy), heat (56 degrees C) and pH 3 lability, cytopathic effects or plaques in cultures of Vero, LLC-MK2, embryonic bovine testicle and PS cells, and pathogenicity for suckling and weaned mice by the intracranial but not the intraperitoneal route. Gnotobiotic and conventional sheep and goats were experimentally infected by inoculation with one of the isolates given either intravenously or intraperitoneally. Elevation of body temperature, depression, tremors, muscle spasms, disorientation, feeding anomalies, convulsions, or other signs of central nervous system disturbances were observed.

Togaviridae and Flaviviridae: The Alphavirases and Flaviviruses

Diseases: Yellow fever, dengue, St. Louis encephalitis, Japanese encephalitis, Wes- selsbron, tick-borne encephalitis, louping ill, Kyasanur Forest disease, other tick- borne hemorrhagic fevers, Murray Valley encephalitis, Rocio encephalitis, equine encephalitides (eastern, western, Venezuelan), chikungunya, o’nyong-nyong, Ross River, Mayaro, Sindbis, Ockelbo.

Bivens arm virus: a new rhabdovirus isolated from Culicoides insignis in Florida and related to Tibrogargan virus of Australia.

During field studies in 1981 on the transmission of bluetongue viruses in ruminants in Florida, a virus was isolated from Culicoides insignis collected near water buffalo (Bubalus bubalis) recently imported from Trinidad. Electron microscopy showed that this isolate, for which the name Bivens Arm virus is proposed, has rhabdovirus morphology. Serologic comparisons were made with recognized rhabdoviruses from terrestrial vertebrates and hematophagous arthropods. Indirect fluorescent antibody, complement fixation and neutralization tests indicated antigenic reactivity between Bivens Arm virus and two rhabdoviruses found only in Australia, Tibrogargan and Coastal Plains viruses. The Australian isolates cause subclinical infections in cattle and water buffalo and are believed to be transmitted by Culicoides. Initially, it was thought that Bivens Arm virus may have been introduced to Florida with the water buffalo from Trinidad, but a serologic survey of cattle serum, collected before the importation of the buffalo revealed antibody to the virus in cattle on farms located in diverse areas of Florida.

Dot-ELISA for serodiagnosis of human infections due to Western equine encephalitis virus☆

A standard dot-ELISA (enzyme-linked immunosorbent assay) was modified for use in detecting IgM and IgG class antibodies to Western equine encephalitis (WEE) virus in serum samples from humans infected with this virus. Nitrocellulose membranes were soaked in supernatant fluid from WEE virus-infected cell cultures, air dried, and blocked with bovine protein. Serum samples were pipetted onto sections of the nitrocellulose, incubated, and washed. Addition of antibody to human immunoglobulin conjugated to alkaline phosphatase and enzyme substrate were used to detect the antibodies. Of 13 samples positive for IgM antibody to WEE virus by IgM antibody capture ELISA, 12 were positive by IgM dot-ELISA. IgG antibody to WEE virus was detected by dot-ELISA in 7/8, 10/14 and 7/10 samples with neutralizing, hemagglutination-inhibiting, or complement-fixing antibodies, respectively.

Use of enzyme immunoassay and nucleic acid hybridization for detecting Sindbis virus in infected mosquitoes

Aedes aegypti mosquitoes were inoculated intrathoracically with prototype Sindbis virus, held at 26.7 degrees C for from 0-95 h and placed at -70 degrees C. Individual mosquitoes were tested for virus by plaque assay in Vero cells, for viral RNA by nucleic acid hybridization using a cloned cDNA probe, and for viral protein by enzyme-linked immunosorbent assay. Virus was detected by plaque assay as early as 8 h after infection. Sindbis virus RNA was detected by nucleic acid hybridization 18 h after infection and by enzyme-linked immunosorbent assay 10 h after infection. The results of these comparisons suggest that both nucleic acid hybridization and enzyme-linked immunosorbent assay are applicable to direct detection of Sindbis virus in mosquitoes containing virus at levels usually found during arbovirus epidemics.

Bunyaviridae: The Bunyaviruses

Diseases: Hemorrhagic fever with renal syndrome, Rift Valley fever, Crimean Congo hemorrhagic fever, Nairobi sheep disease, Oropouche, LaCrosse encephalitis, Akabane, sandfly fever, and undifferentiated fevers.

Cell cultures for diagnosis of arbovirus infections in livestock and wildlife

Arboviruses can be isolated in serially propagated cells derived from various vertebrates and invertebrates. Cell cultures can be used for direct detection of antigen by fluorescent antibody and enzyme-linked immunosorbent assays, for nucleic acid hybridization, and for visualization of viruses with electron microscopy. Reagents for enzyme-linked immunosorbent assays for IgM and IgG antibodies, hemagglutination-inhibition, complement fixation, and serum dilution-plaque reduction neutralization tests can be prepared in cell cultures infected with these viruses. Thus, cell cultures can be used as laboratory hosts for essentially all isolation, identification, and serodiagnostic procedures for arboviruses. This paper outlines current methods for diagnosis of arbovirus infections in livestock and wildlife, describes certain of these techniques, and provides references for others.