Potential for Central American mosquitoes to transmit epizootic and enzootic strains of Venezuelan equine encephalitis virus

Experimental studies were undertaken to compare the vector competence of Culex (Melanoconion) taeniopus Dyar and Knab, Culex (Melanoconion) ocossa Dyar and Knab, and Psorophora confinnis (Lynch Arribalzalga) from Central America for epizootic (IAB) and enzootic (IE) strains of Venezuelan equine encephalitis (VEE) virus. Virus infection and dissemination rates were significantly higher in Cx. taeniopus orally exposed to IE as compared to those orally exposed to IAB virus. In contrast, both infection and dissemination rates were similar in Cx. ocossa exposed to either IAB or IE strains of VEE virus. Thus, susceptibility to epizootic and enzootic strains of VEE virus seems to be species specific within the subgenus Culex (Melanoconion). Both species transmitted each strain of VEE virus after intrathoracic inoculation, indicating that a midgut barrier affected vector competence in these species. Psorophora confinnis was equally susceptible to both IAB and IE viruses, but apparently had a salivary gland barrier, as only 1 of 16 mosquitoes with a disseminated infection transmitted VEE virus by bite.

Vector competence of three Venezuelan mosquitoes (Diptera: Culicidae) for an epizootic IC strain of Venezuelan equine encephalitis virus

Experimental studies were undertaken to evaluate the vector competence of selected mosquito species [Aedes taeniorhynchus (Wiedemann), Culex declarator Dyar and Knab, and Mansonia titillans (Walker)] from northwestern Venezuela for the epizootic (IC) strain of Venezuelan equine encephalitis (VEE) virus that was responsible for the 1995 outbreak of VEE in this area. Ae. taeniorhynchus was highly susceptible to infection (94% of 35), and 89% had a disseminated infection. Virus-exposed Ae. taeniorhynchus that refed on susceptible hamsters readily transmitted virus, confirming that this species was an efficient vector of VEE virus. In contrast, only 1 of 28 (4%) Cx. declarator was infected, and that individual did not develop a disseminated infection. Ma. titillans was moderately susceptible (3 of 8 infected, 38%), and 2 (25%) of these had a disseminated infection. These data indicate that Ae. taeniorhynchus was an important epizootic vector during the 1995 VEE outbreak in Columbia and Venezuela.

Comparative effects of beta-propiolactone on mice, mouse-derived cell cultures, and Venezuelan equine encephalomyelitis virus

Studies were made comparing the toxicity of beta-propiolactone (BPL) for mammalian (mouse) cells in vitro and for mice and for Venezuelan equine encephalomyelitis (VEE) virus which is highly cytopathogenic for each. The mammalian cells grown in tissue culture were found to be adversely affected by BPL in concentrations ranging from 0.001 to 0.1 mg/ml of supernatant fluid. The difference in response was influenced by the menstruum in which the BPL was suspended and the difference in cell types tested. Tenfold less BPL appeared to be required to destroy the cells when it was suspended in a balanced salt solution than when it was suspended in protein-containing solutions such as beef heart infusion broth or medium 199 plus 20% horse serum. Secondary embryonic mouse lung cells seemed slightly more adversely affected by BPL than the established embryonic lung or L cells. BPL given to mice by intranasal instillation and by intracerebral injection was lethal to half of the animals within 2 days at doses of 0.31 and 0.39 mg, respectively. Higher concentrations of BPL were required to rapidly inactivate the virus in vitro than were required to kill mice or to cause a toxic effect on cells in culture. It required 10 mg/ml of BPL to completely inactivate a high-titered VEE virus preparation in 5 min and 1 mg/ml to inactivate most, but not all, of the virus in 15 min. A concentration of 0.1 mg/ml of BPL had only a slight effect on the virus after a period as long as 60 min. Evidence is presented indicating that simultaneous inactivation of all of the properties of the VEE virus particles by BPL aerosols did not occur at the same time but that, after treatment, the virus possessed a limited ability to immunize mice despite a loss in infectivity.

EFFECT OF ADJUVANTS ON ANTIBODY RESPONSE OF RABBITS INOCULATED WITH VENEZUELAN EQUINE ENCEPHALOMYELITIS VIRUS

Shepel, Michael (U.S. Army Biological Laboratories, Fort Detrick, Frederick, Md.) and Maxwell R. Klugerman. Effect of adjuvants on antibody response of rabbits inoculated with Venezuelan equine encephalomyelitis virus. J. Bacteriol. 85:1150-1155. 1963.-Hemagglutination-inhibition, neutralization, and complement-fixation tests were performed on sera of rabbits inoculated with Venezuelan equine encephalomyelitis (VEE) virus in combination with Freund's adjuvants and in Hank's salt solution. This study indicated that the complete adjuvants (i.e., with mycobacteria) considerably increased the antibody response to VEE virus. Mycobacterium butyricum (M. smegmatis) appeared to be more effective than M. tuberculosis H37Ra. In the absence of mycobacteria, the response was much less pronounced. Paper electrophoretic studies of the antisera demonstrated a marked increase in gamma-globulin production, an increase in the beta-globulin, and an increase in total protein as the result of adding VEE virus to the complete adjuvants. A decrease in the albumin fraction appeared to be caused by the complete adjuvants rather than by the VEE virus itself. The incomplete adjuvant (without mycobacteria) plus virus contributed little, if any, stimulation toward the production of gamma-globulin, nor did it appear to affect the serum-albumin levels.

Arbovirus investigations in Argentina, 1977-1980. I. Historical aspects and description of study sites

This is the introductory paper to a series on the ecology of arboviruses in Argentina. Epizootics of equine encephalitis have occurred since at least 1908, principally in the Pampa and Espinal biogeographic zones, with significant economic losses; human cases of encephalitis have been rare or absent. Both western equine and eastern equine encephalitis viruses have been isolated from horses during these epizootics, but the mosquitoes responsible for transmission have not been identified. A number of isolations of Venezuelan equine encephalitis (VEE) virus were reported between 1936 and 1958 in Argentina, but the validity of these findings has been seriously questioned. Nevertheless, serological evidence exists for human infections with a member of the VEE virus complex. Serological surveys conducted in the 1960s indicate a high prevalence of infection of humans and domestic animals with St. Louis encephalitis (SLE), and 2 SLE virus strains have been isolated from rodents. Human disease, however, has rarely been associated with SLE infection. Only 7 isolations of other arboviruses have been described (3 of Maguari, 1 of Aura, 2 of Una, and 1 of an untyped Bunyamwera group virus). In 1977, we began longitudinal field studies in Santa Fe Province, the epicenter of previous equine epizootics, and in 1980 we extended these studies to Chaco and Corrientes provinces. The study sites are described in this paper.

Experimental models of virus-induced demyelination of the central nervous system

One of the arguments in favor of a viral pathogenesis for multiple sclerosis is the existence of several experimental and natural animal models of virus-induced primary demyelination. This review deals comprehensively with such models. Well-known examples of demyelinating viral infections in their natural host are JHM, Theiler, visna, and canine distemper encephalomyelitides. Recent reports of experimental murine infections with pathogens such as vesicular stomatitis, Chandipura, herpes simplex, Venezuelan equine encephalomyelitis, and Semliki Forest viruses are also discussed. The thrust of the review is to include viral models suspected of producing primary demyelination on an immunopathological basis.

[Use of continuous human lymphoblastoid cell lines (T- and B-origin) to produce persistent tick-borne encephalitis virus and Venezuelan equine encephalomyelitis virus infections]

Persistent infection with tick-borne encephalitis virus (TBE) was established in experimentally infected continuous lymphoblastoid human cell lines Raji, L-101 (of B-origin) and 1387 (T-origin) and with Venezuelan equine encephalomyelitis (VEE) virus in Raji and 1387 lines. The persistently infected lines produced infectious virus, the cells showed specific fluorescence in immunofluorescent tests, and electron microscopic examinations revealed TBE and VEE virions in sections.

[Stimulation of interferon formation by natural and synthetic inducers in cultures of human tonsil cells]

Conditions of interferon production stimulation were studied in human tonsillar cell cultures exposed to natural and synthetic inducers : poly(I) . poly(C), phage f2 RNA replicase, phytohemagglutinin and the low-molecular inducer gossypol (beta-aminoethyl sulfoxide Na). It has been shown that being inferior in the productivity per one cell to the continuous lymphoblastoid Raji and Namalva cell liness the tonsillar cell cultures, due to their high density, produce rather high interferon titers reaching hundreds of IU50/ml. The viability of the tonsillar cell cultures and their incubation at 37 degrees C during 24 hours are rather important for adequate interferon production.

Venezuelan encephalitis virus-induced alterations in carbohydrate metabolism in geneticaly diabetic mice

We previously reported in this journal that the TC-83-vaccine strain of Venezuelan encephalitis (VE) virus results in a sustained diminution of glucose-stimulated insulin release in golden Syrian hamsters, persisting as long as 90 days after viral infection. This study was designed to examine the metabolic and pathologic consequences of TC-83 VE virus infection in C57 BL/Ks mice (+/+) and in genetic variants of this strain homozygous (db/db) and heterozygous (db/+) for the diabetic gene, db. Five-week-old mice of each genetic variant were inoculated subcutaneously, in groups of 18, with 100,000 plaque-forming units (PFU) of TC-83 that had not been passaged in chick embryo cells or with diluent (control mice). The clinical course in all three groups of mice following VE inoculation was mild, with a 5 to 10% mortality. By light microscopy, control +/+, TC-83 VE-infected +/+, control db/+, and TC-83 VE-infected db/+ pancreases manifested no appreciable difference in morphology. Uninfected db/db mice showed typical changes, including a definite decrease in the number of aldehyde fuchsin-staining granules in beta cells. TC-83 VE-infected db/db mice exhibited a profound decrease in pancreatic beta cell granulation on aldehyde fuchsin staining. After TC-83 VE inoculation, the most striking alterations in carbohydrate metabolism occurred in db/db mice, which showed further worsening of glucose tolerance 120 min after intraperitoneal glucose as well as significantly decreased basal and glucose-stimulated immunoreactive insulin (IRI) levels. After TC-83 VE infection, pancreatic IRI content was not decreased in +/+ or db/+ mice but was virtually absent in db/db mice. The data support the ability of TC-83 VE to inhibit glucose-stimulated IRI release in three genetic variants of C57 BL/Ks mice. In addition, this model demonstrates the heightened susceptibility of the remaining diabetic beta cells in the db/db mice to subsequent infection with a pancreatropic virus.

[Stimulation of interferon production]

Data on the effect of some factors on interferon production in vitro are presented The kinetics of interferon synthesis in response to superinduction was similar to the respective curve of the effect of UV-radiation on the cell. Possible similarity in the effect of these factors on the mechanisms controlling interferon production is noted. An increase in interferon synthesis under the effect of ascorbic acid in cells of chick embryo fibroblast and L-929 was found. Combined use of the inductors provided an increase in the tests of interferon.

[Enzymatic and ultrastructural changes in isolated liver mitochondria from mice infected with several group A arboviruses]

Inoculation of white mice of varying body mass with pathologic strains of eastern and Venezuelan equine encephalomyelitis viruses and their attenuated variants (DNC-20/6 and No. 2621), promising as vaccine candidates, resulted in an increase of enzymatic activity and ultrastructural changes of isolated mitochondria from livers of the animals. The attenuated strains of the viruses were shown to induce temporary changes in both aspects of the study which became normal by the end of the study. There was a certain correlational dependence between the enzymatic activity and ultrastructural changes in isolated mitochondria associated with the use of energy in virus reproduction.

Venezuelan encephalitis virus infection in neotropical bats. III. Experimental studies on virus excretion and non-arthropod transmission

A total of 80 Neotropical bats of five species was inoculated with one of four strains of Venezuelan encephalitis (VE) virus. Virus was detected in the oropharynges of 56% of bats, and most regularly in Artibeus jamaicensis (75%). Titers of virus in oropharyngeal secretions were occasionally very high (8.5 log10 SMicLD50/ml in one A. jamaicensis). Only 2 of 123 urine samples from 50 bats and 2 of 86 fecal samples from 46 bats yielded VE virus. No contact or aerosol virus transmission from bat to bat was detected. VE virus passed transplacentally from two infected mothers to their fetuses, which were aborted. Virus did not pass from one infected mother to her nursing young.

[Superinduction of interferon and and a study of its messenger RNA]

Combined use of interferon inductor poly-IC and antibiotics (cycloheximide and actinomycin D) provided a significant increase (up to 1000 times) in interferon production by chick, mouse, monkey and human cells. Messenger RNA with matrix activity for interferon (mRNA-IF) was isolated from superinduced cells. On translation of mRNA-IF in homogenous and heterogenous cells the specificity of interferons produced was determined by the type of the cells from which mRNA-IF was isolated. Sedimentation analysis of various mRNA-IF revealed 2 peaks of activity: major (5--15S) and minor (25--30S).

[Reproduction and interferogenic activity of togaviruses]

A comparative study of the correlation between reproduction and the interferon-inducing activity of viruses in chick embryo fibroblast cultures was carried out with members of different groups of togaviruses: alphavirus (Venezuelan equin encephalomyelitis viru, VEE) and flavivirus (Saint Louis encephalitis virus, SLE). The correspondence between cycles of accumulation of intracellular and extracellular viruses and the dynamics of interferon production the synthesis of which began early in the stage of exponential virus growth and correlated with the dynamics of their reproduction, was determined. Reproduction of the viruses was found to be directly dependent upon the multiplicity of infection; optimal infecting doses for the induction of the largest amounts of interferon were established. The calculations of the reproductive activity of VEE and SLE viruses showed their yield per one cell to be approximately 10,000 PFU and 1,000 LD50, respectively. Partial thermal inactivation of the viruses resulted in decreased yields of the infectious virus and interferon production. The regimen of thermal inactivation at which infectivity was lost completely, but the interferon-inducing capacity was retained probably due to residual synthesis of viral RNA was established for VEE virus. From the fact that the pattern of realization of genetic information is similar for both viruses, a similar mechanism of interferon synthesis induction is assumed.

Survival of arboviruses in trypanosome-infected triatomines

The potential of triatomines to maintain arboviruses was demonstrated by the ability of Rhodinius prolixus with experimentally punctured abdomen to harbor Venezuelan equine encephalitis (VEE) virus for at least 4 months and St. Louis encephalitis virus for 1 month. At 30 days after infection VEE virus was found at low titers in Trypanosoma cruzi-infected R. prolixus and at moderate titers in T. rangeli-infected R. neglectus. Transmission of VEE virus by bite of punctured bugs was successful 2 weeks after virus ingestion; attempts at 30 days failed.

Virus-induced pancreatic disease by Venezuelan encephalitis virus. Alterations in glucose tolerance and insulin release

Viral infections have been implicated in the induction of diabetes mellitus in man and laboratory animals. Since virus-specific immunofluorescence (FA) is detectable in hamster pancreas during the acute phase of Venezuelan encephalitis (VE), experiments were designed to correlate pathologic and virologic events with metabolic studies in VE-infected hamsters. Golden Syrian hamsters were inoculated s.c. in groups of four to 12 with 100,000 plaque-forming units (PFU) of the vaccine strain (TC-83) of VE or 1,000 PFU of the virulent Trinidad strain of VE. Ultrastructurally, during Trinidad infection, mature virions were associated with the cell surfaces and within pancreatic beta cells in contrast to absence of virus-related changes in TC-83-infected hamsters. Virus-specific-FA was noted in islet cells and acinar cells of Trinidad-infected hamsters. VE growth curves demonstrated viral replication in pancreas with both strains. Although ultrastructural and FA changes were much more prominent in Trinidad-infected hamsters in contrast to TC-83-infected hamsters during the first few days of illness, the rapid lethality of the Trinidad-infected group necessitated performing all metabolic studies in TC-83-strain-infected hamsters. Accordingly, for the metabolic studies, glucose tolerance tests (GTT) using 2 mg. or 5 gm./kg. glucose i.p. were performed in groups of hamsters acutely infected two days earlier with the TC-83 vaccine strain and in 24-day and 90-day convalescent hamsters after TC-83 vaccine strain. Samples were obtained for glucose and immunoreactive insulin (IRI) determinations. Glucose intolerance occurred in hamsters in each of the infected groups given 5 gm./kg. glucose except for the 90-day convalescent TC-83 group. Severely decreased IRI responses occurred in the 24-day and 90-day convalescent TC-83 hamsters following both 2- and 5-gm./kg. glucose. Pancreatic IRI content in 24-day convalescent TC-83 hamsters was within normal limits, suggesting a defect in IRI release from the beta cells at this stage of convalescence.