Transovarial transmission of Gamboa virus in a tropical mosquito, Aedeomyia squamipennis.

We report transovarial transmission of Gamboa virus (Bunyavirus) in Aedeomyia squamipennis, a tropical mosquito which is active and bloodfeeding throughout the year. Gamboa virus was isolated during each of the 28 months of the study from every mosquito stage, including eggs, demonstrating that vertical transmission is a maintenance mechanism of this virus. The overall minimum infection rate was 5.1/1,000 mosquitoes. Identification of the 567 isolates by neutralization indicated that greater than or equal to 2 serotypes or subtypes of Gamboa virus circulate at the study site.

A human case of encephalitis associated with vesicular stomatitis virus (Indiana serotype) infection.

This paper describes a case of severe encephalitis in a 3-year-old Panamanian boy infected with the Indiana serotype of vesicular stomatitis virus. The virus was recovered from the child's throat on the fifth day of illness and a rise in neutralizing antibody titer was demonstrated in paired serum specimens. This is the second report of childhood encephalitis associated with vesicular stomatitis virus infection. These suggest that infection with vesicular stomatitis viruses may cause severe disease. Human infection with vesicular stomatitis viruses is common throughout the tropical Americas.

Characterization of the Changuinola serogroup viruses (Reoviridae: Orbivirus).

The antigenic, biological, and chemical properties of 24 selected Changuinola serogroup viruses were examined. The viruses tested were chloroform-resistant, and they were lethal to newborn hamsters after intracerebral inoculation. The prototype Changuinola virus strain (BT-436) replicated in mosquito and sandfly cell cultures. In complement-fixation tests, the viruses were broadly cross-reacting and indistinguishable; but by neutralization test at least 12 distinct serotypes were identified, and by PAGE of double-stranded RNA 22 distinct profiles were found. These data suggest that the Changuinola serogroup may be comprised of a large number of genetically different viruses. A brief review of the natural history of Changuinola serogroup viruses is also given.

Viruses isolated from Panamanian sloths.

Seven virus strains were isolated in Vero cells from whole blood samples from 80 wild-caught sloths, Bradypus variegatus and Choloepus hoffmanni, from Central Panamá. Four strains of at least two different serotypes are related to Changuinola virus; two of these were associated with prolonged or recrudescent viremias. One strain is an antigenic subtype of Punta Toro virus, and another, described here as Bradypus-4 virus, is a new, antigenically ungrouped virus. A second new virus from sloths, Utive virus, forms an antigenic complex within the Simbu serogroup with Utinga and Pintupo viruses. Tests on sequential plasma samples from radio-marked free-ranging sloths and from recently captured animals maintained in captivity showed that both species develop neutralizing antibodies following naturally acquired virus infections. Antibodies against the Changuinola and Simbu serogroup viruses are widespread in both sloth species and are especially prevalent in Choloepus, but are virtually absent in all other wild vertebrate species tested.

Experimental St. Louis encephalitis virus infection of sloths and cormorants.

Experimental infection of 11 Bradypus variegatus and Choloepus hoffmanni sloths with St. Louis encephalitis (SLE) virus produced detectable viremias of seven to 27 (median 13) days duration and maximum titers of 2.7 to 6.5 (median 5.1) log10 median suckling mouse intracranial lethal doses (SMicLD50) per ml. Experimental SLE viremia onset was delayed and maximum titer depressed in two sloths concurrently infected with naturally acquired viruses. SLE viremias in four experimentally inoculated cormorants Phalacrocorax olivaceus were shorter, and of equal or lower titer, than in sloths. Colonized Culex pipiens quinquefasciatus mosquitoes were infected by feeding on sloths circulating at least 4.8 log10 SMicLD50 of SLE virus per ml, and subsequently transmitted the infection to mice and chicks. An uninoculated baby Bradypus became infected by contact transmission from its mother. The antibody response of sloths to SLE virus was slow, being undetectable until several weeks post-inoculation. However, both sloth species developed high and long-lasting neutralizing and hemagglutination-inhibition antibody titers. The complement-fixation antibody response in Bradypus was lower and slower to develop than in Choloepus. Sloths with naturally acquired SLE virus antibody did not become detectably viremic after experimental inoculation. Neither sloths nor cormorants become overly ill from SLE virus infection.

Serologic evidence of natural togavirus infections in Panamanian sloths and other vertebrates.

Plasmas of sloths and other Central Panamanian wild vertebrates were tested for plaque-reduction neutralizing (PRN) antibodies against four flaviviruses and one alpha-virus. Forty percent of 97 two-toed sloths, Choloepus hoffmanni, and 8% of 168 three-toed sloths, Bradypus variegatus, were specifically positive against St. Louis encephalitis (SLE) virus. The prevalence of antibody against SLE virus was considerably higher in sloths than in any other group of wild vertebrates tested, including birds, and was found mainly in adult sloths. Specific PRN antibody against yellow fever (YF) virus was found only in monkeys. A high prevalence of PRN antibody against Ilheus and Mayaro viruses was detected in agoutis, Dasyprocta punctata, and against Mayaro virus in howler monkeys, Alouatta villosa. No plasma was specifically positive against Bussuquara virus. The results are interpreted as evidence that sloths are probably not important hosts in jungle YF cycles, but may be significant amplifying hosts in tropical SLE virus cycles.

Ten clinical cases of human infection with venezuelan equine encephalomyelitis virus, subtype I-D.

The clinical and laboratory findings in ten humans infected with Venezuelan equine encephalitis virus, subtype I-D, are described in this report. Clinical and laboratory data indicate that, in contrast to equine infections, human infection with these enzootic virus strains (I-D) is similar to human infection with epizootic strains (I-ABC). In most cases there was an abrupt onset of fever, muscle pain, and vomiting. Virus was recovered from sera obtained during the first 3 days of illness. Lymphopenia occurred in all patients, and neutropenia occurred in three. No sequelae of these infections were apparent.

Isolations in a mosquito (Aedes pseudoscutellaris) cell line (Mos. 61) of yellow fever virus strains from original field material.

A simple, rapid and inexpensive method of isolating yellow fever (YF) virus from naturally infected mosquitoes, human liver and the serum of a sentinel monkey by inoculation of a continuous line of mosquito cells is described. The mosquito cells were more sensitive than suckling mice and marginally better than Vero cells for primary isolation. This is the first time that mosquito cells have been successfully used for primary isolation of YF virus from field material.

Antigenic relationships among phlebotomus fever group arboviruses and their implication for the epidemiology of sandfly fever.

The antigenic relationships of 21 known or presumed Phlebotomus fever group serotypes and of 2 ungrouped, solvent sensitive, sandfly-associated arboviruses (Pacui and Charleville) were studied by complement fixation, plaque neutralization, and hemagglutination-inhibition methods. Results of complement fixation and neutralization tests were specific, allowing clear separation of the various serotypes, while those of the hemagglutination-inhibition test showed broader crossing and lack of specificity. Pacui virus was shown to be a member of the Phlebotomus fever serogroup. Six new Phlebotomus fever group serotypes are also described, increasing the known members of the group to 22. The implications of these and other recent data about the epidemiology of sandfly fever are discussed.