Phylogenetic analysis of alphaviruses in the Venezuelan equine encephalitis complex and identification of the source of epizootic viruses.

We studied the evolution of alphaviruses in the Venezuelan equine encephalitis (VEE) complex using phylogenetic analysis of RNA nucleotide sequences from limited portions of the nsP4, E1, and 3' untranslated genome regions of representative strains. The VEE complex constituted a monophyletic group of viruses (descended from a common ancestor); some serologic VEE varieties such as subtype III formed monophyletic groups while subtype I did not. Subtype II Everglades and variety ID enzootic viruses formed a monophyletic group which also included all epizootic variety IAB and IC VEE isolates. Everglades virus diverged from this ID lineage (colonized North America) ca. 100-150 years ago, followed by divergence of variety IAB and IC epizootic viruses. Variety IAB viruses probably emerged from the variety ID lineage once during the early part of this century, while variety IC viruses evolved at least two times. These results identify the source of epizootic VEE viruses as the variety ID enzootic virus lineage which occurs in northern South America and Panama. Even if variety IAB and IC viruses are extinct, recent, multiple emergences of epizootic viruses from an enzootic lineage suggests that other epizootic VEE viruses may evolve again in the future. The close genetic relationship of subtype II Everglades virus to the variety ID lineage also implies the potential for emergence of equine-virulent VEE viruses in Florida.     

Genetic targets for the detection and identification of Venezuelan equine encephalitis viruses

Summary.  Rt-PCR probes targeted to different gene sequences of VEE (Venezuelan equine encephalitis) virus strain TC-83 were assessed for their sensitivity, specificity and non-specific cross-reactivity. A generic VEE virus amplimer (VNSP4F2/VNSP4R2), targeted against nsP4 was identified, which was sensitive (detected at least 10 pfu) and robust (worked over a wide range of salt concentrations and annealing temperatures). An E2 amplimer designed against TC-83, (VE2F/VE2R), identified VEE strains TRD (1AB), P676 (1C), 3880 (1D) Everglades (2) vRNA whilst a second E2 primer pair designed against strain 68U201, (68UF/68UR), identified all the remaining VEE viruses in the sero-complex. This would suggest that the VEE virus E2 gene can be sub-divided at the genetic level into two separate groups making it a useful target for differentiation of sero-subtypes 1 and 2 from the other VEE virus subtypes. Using a panel of amplimers targeted to different VEE genes and strains it was possible to distinguish between most of the serotypes, but most importantly, we were able to detect the epizootic strains TRD and P676 as well as other VEE viruses implicated in human disease (sero-subtypes 1D and 1E). Accepted November 13, 1997 Received August 24, 1997     

Equine arteritis virus-infected cells contain six polyadenylated virus-specific RNAs

Fluorescamine-labeled structural proteins of viruses in the Venezuelan equine encephalitis (VEE) serologic complex were purified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Purified [¹⁴C]lysine-labeled capsid protein and El and E2 envelope glycoproteins of TC-83 (serologic subtype-variant I-A) virus were mixed with the corresponding [³H]lysine-labeled structural proteins of TC-83, PTF-39 (I-B), P676 (I-C), 3880 (I-D), Mena II (I-E), Everglades Fe 3–7c (II), Mucambo BeAn 8 (III), and Pixuna BeAr 35645 (IV) viruses and codigested with trypsin. Tryptic peptides were resolved by reverse-phase high-pressure liquid chromatography. The capsid and El proteins of I-A, I-B, I-C, and I-D viruses produced identical or nearly identical tryptic peptide maps, whereas the maps of I-E, II, III, and IV capsid and El proteins were distinct from the maps of the corresponding I-A proteins. The tryptic peptide maps of the type-specific protein, E2, of the various viruses showed the most variation and correlated well with the serologic and genetic homologies determined by oligonucleotide fingerprinting of VEE 42 S RNA. Fluorescamine derivatization of viral proteins was shown to have little or no effect on the specificity of trypsin. Trypsin was shown to cleave these proteins at both lysine and arginine residues.     

Experimental Infection of Horses with an Attenuated Venezuelan Equine Encephalomyelitis Vaccine (Strain TC-83)

Ten horses (Equus caballus) were vaccinated with strain TC-83 Venezuelan equine encephalomyelitis (VEE) virus vaccine. Febrile responses and leukopenia due to a reduction of lymphocytes and neutrophils were observed in all animals. Viremias were demonstrable in eight horses, with a maximum of 10(3.5) median tissue culture infectious dose units per ml of serum in two horses. Clinical illness with depression and anorexia were observed in five horses. Neutralizing (N), hemagglutination-inhibiting, and complement-fixing antibodies to the vaccine virus were demonstrable by 5, 6.5, and 7 days, respectively, after vaccination. Differential titrations of serum to six VEE strains revealed high titers of N antibody to vaccine virus, moderate titers to the epizootic Trinidad donkey no. 1 strain (VEE antigenic subtype I, variant A) from which TC-83 was derived, and low titers to two other epizootic strains (subtype I, variants B and C) in all horses at 1 month after vaccination; some animals responded with low levels of N antibody to the enzootic viruses (subtype I, variants D and E). Fourteen months after vaccination, six animals with detectable N antibody were challenged with MF-8 (subtype I, variant B), an epidemic-epizootic strain isolated in 1969 from a man in Honduras. All horses resisted challenge with the equine pathogenic strain of VEE. Marked increases of N antibody in most horses were demonstrable to some VEE strains when tested 1 month after challenge.     

Vector competence of Mexican and Honduran mosquitoes (Diptera: Culicidae) for enzootic (IE) and epizootic (IC) strains of Venezuelan equine encephalomyelitis virus

Experimental studies evaluated the vector competence of Ochlerotatus taeniorhynchus (Wiedemann), Culex cancer Theobald, Culex pseudes (Dyar and Knab), Culex taeniopus Dyar and Knab, and a Culex (Culex) species, probably Culex quinquefasciatus Say, and Culex nigripalpus Theobald from Chiapas, Mexico, and Tocoa, Honduras, for epizootic (IC) and enzootic (IE) strains of Venezuelan equine encephalomyelitis (VEE) virus. Culex pseudes was highly susceptible to infection with both the IC and IE strains of VEE (infection rates >78%). Patterns of susceptibility to VEE were similar for Oc. taeniorhynchus collected in Mexico and Honduras. Although Oc. taeniorhynchus was highly susceptible to the epizootic IC strains (infection rates > or = 95%, n = 190), this species was less susceptible to the enzootic IE strain (infection rates < or = 35%, n = 233). The Culex (Culex) species were refractory to both subtypes of VEE, and none of 166 contained evidence of a disseminated infection. Virus-exposed Cx. pseudes that refed on susceptible hamsters readily transmitted virus, confirming that this species was an efficient vector of VEE. Although Oc. taeniorhynchus that fed on hamsters infected with the epizootic IC strain transmitted VEE efficiently, only one of six of those with a disseminated infection with the enzootic IE virus that fed on hamsters transmitted virus by bite. These data indicate that Cx. pseudes is an efficient laboratory vector of both epizootic and enzootic strains of VEE and that Oc. taeniorhynchus could be an important vector of epizootic subtypes of VEE.     

Susceptibility of Ochlerotatus taeniorhynchus (Diptera: Culicidae) to infection with epizootic (subtype IC) and enzootic (subtype ID) Venezuelan equine encephalitis viruses: evidence for epizootic strain adaptation

To test the hypothesis that adaptation to epizootic mosquito vectors mediates emergence of Venezuelan equine encephalitis virus (VEEV) from enzootic progenitors, experimental infection studies were conducted to determine the susceptibility of Ochlerotatus taeniorhynchus (Wiedemann) to epizootic and enzootic strains. Artificial blood meals containing epizootic subtype IC strains isolated during the 1962-1964, 1992-1993, and 1995 Venezuelan/Colombian epizootics and closely related Venezuelan enzootic subtype ID strains were used to compare infectivity and transmission potential. Their greater infectivity and replication suggested that adaptation of epizootic strains to Oc. taeniorhynchus may have enhanced epizootic transmission during the 1962-1964 and 1995 IC coastal epizootics. However, strains from the small 1992-1993 Venezuelan outbreak that did not extend to coastal regions do not seem to infect this species better than closely related subtype ID strains. Adaptation of VEEV to epizootic vectors such as Oc. taeniorhynchus mosquitoes may be a determinant of some but not all VEE emergence events and may influence spread into coastal regions.     

Susceptibility of Psorophora confinnis (Diptera: Culicidae) to infection with epizootic (subtype IC) and enzootic (subtype ID) Venezuelan Equine encephalitis viruses

To test the hypothesis that adaptation to epizootic mosquito vectors mediates the emergence of Venezuelan equine encephalitis virus (family Togaviridae, genus Alphavirus, VEEV) from enzootic progenitors, the susceptibility of the epizootic vector Psorophora confinnis (Lynch-Arribalzaga) to epizootic versus enzootic strains was evaluated. Artificial bloodmeals containing subtype IC strains isolated during the 1962-1964, 1992-1993, and 1995 Venezuelan/Colombian epizootics and closely related Venezuelan enzootic subtype ID strains were used to compare mosquito infectivity and transmission potential. Strains from the smaller 1992-1993 epizootic showed lower or equal infectivity and replication compared with enzootic viruses and to strains isolated during the larger 1962-1964 and 1995 epizootics. These experiments failed to provide evidence that Ps. confinnis selects for epizootic VEEV viruses with higher infectivity, as has been shown for Aedes (Ochlerotatus) taeniorhynchus (Wiedemann). Nonetheless, its high susceptibility, abundance in enzootic and epizootic regions, and feeding behavior suggest that Ps. confinnis is an important bridge vector for both enzootic and epizootic VEEV.     

Sequencing of prototype viruses in the Venezuelan equine encephalitis antigenic complex.

The 5' nontranslated region (5'NTR) and nonstructural region nucleotide sequences of nine enzootic Venezuelan equine encephalitis (VEE) virus strains were determined, thus completing the genomic RNA sequences of all prototype strains. The full-length genomes, representing VEE virus antigenic subtypes I-VI, range in size from 11.3 to 11.5 kilobases, with 48-53% overall G+C contents. Size disparities result from subtype-related differences in the number and length of direct repeats in the C-terminal nonstructural protein 3 (nsP3) domain coding sequence and the 3'NTR, while G+C content disparities are attributable to strain-specific variations in base composition at the wobble position of the polyprotein codons. Highly-conserved protein components and one nonconserved protein domain constitute the VEE virus replicase polyproteins. Approximately 80% of deduced nsP1 and nsP4 amino acid residues are invariant, compared to less than 20% of C-terminal nsP3 domain residues. In two enzootic strains, C-terminal nsP3 domain sequences degenerate into little more than repetitive serine-rich blocks. Nonstructural region sequence information drawn from a cross-section of VEE virus subtypes clarifies features of alphavirus conserved sequence elements and proteinase recognition signals. As well, whole-genome comparative analysis supports the reclassification of VEE subtype-variety IF and subtype II viruses.     

Immunochemical and oligonucleotide fingerprint analyses of Venezuelan equine encephalomyelitis complex viruses.

RNA oligonucleotide fingerprint analyses indicate that the genome RNA obtained from Trinidad donkey (TRD) Venezuelan equine encephalomyelitis (VEE) virus serotype I A, its vaccine strain derivative TC-83, and the VEE I B virus isolate PTF-39, have almost identical patterns of characteristic ribonuclease T1 resistant oligonucleotides. The TC-83 strain and the I B isolate can, on the basis of these analyses, be considered as variants of the TRD virus and categorized as I AB serotypes. Comparisons made by single and co-electrophoreses of the ribonuclease T1 digests of the RNA species of TC-83 and a VEE I C isolate P676 indicate that 16 of 37 large oligonucleotides of the TC-83 virus co-migrate with the oligonucleotides obtained from the I C isolate. Similar single and co-electrophoreses of ribonuclease T1 digests of the RNA species of TC-83 and a VEE I D isolate 3880 indicate that 18 of 41 TC-83 large oligonucleotides co-migrate with the oligonucleotides obtained from the I D virus isolate. At least nine of the TC-83 large oligonucleotides appear on the basis of these analyses, to be present in the digests of the genome RNA obtained from these selected I B, I C and I D virus isolates. The ribonucleast T1 digests of three I E virus isolates (Mina II, 63U2 and 71U388) give oligonucleotide fingerprints which, although comparable to each other, are more distinct from the I A and I B RNA fingerprints than are those of the I C and I D RNA species. The ribonuclease T1 resistant oligonucleotide fingerprints of VEE virus isolates belonging to serotypes (VEE subtypes) II, III and IV show little similarity to each other or to those of the serotype I virus isolates we have studied. The results obtained here agree with the reported close antigenic relationships of VEE, I A, I B, I C and I D virus isolates, and our studies suggest that these viruses have conserved nucleotide sequences. The I E virus isolates appear to have more distinct nucleotide sequences than do the other serotype 1 viruses. The results also agree with the serological differentiation of VEE, I, II, III and IV subtypes in that the oligonucleotide fingerprints of subtypes II to IV are different from each other and from those of the different serotype I virus isolates. On the basis of antigenic and genome relationships, VEE isolates can be classified as serotypes I to IV with serotype I viruses differentiated into the categories I AB, I C, I D and I E.     

Comparative infections of epizootic and enzootic strains of Venezuelan equine encephalomyelitis virus in Amblyomma cajennense (Acari: Ixodidae).

To compare the potential for an enzootic or an epizootic strain of Venezuelan equine encephalomyelitis (VEE) virus to infect Amblyomma cajennense (F.), larval ticks were fed on guinea pigs (strain 13) inoculated with an enzootic viral strain of variant I-E (68U201) or on guinea pigs inoculated with an epizootic strain of variant I-A (Trinidad donkey). Peak viremias were 10(5.2) plaque-forming units (PFU)/ml and 10(7.3) PFU/ml in guinea pigs infected with enzootic and epizootic viral strains, respectively. Ticks feeding on enzootic- and epizootic-infected hosts had viral titers of 10(2.5) and 10(3.9) PFU per tick, respectively, at drop-off. Although epizootic virus was recovered from 98% (127 of 130) of larval ticks up to 16 d after drop-off, enzootic virus was recovered from 95% (19 of 20) at drop-off (mean titer, 10(2.5) PFU per tick), with recovery rates declining rapidly to 2 of 10 (mean titer, 10(1.4) PFU per tick) by 16 d after drop-off. Transstadially transmitted epizootic virus was found in 0.4% (12 of 2,950) of unfed nymphs (mean titer, 10(2.8) PFU per tick) 63 d after drop-off, 1% (5 of 521) fed nymphs 69 d after drop-off, and 1% (4 of 400) of unfed adults (mean titer, 10(3.6) PFU per tick) 106 d after drop-off. No enzootic virus was recovered from 4,600 unfed nymphs tested 63 d after drop-off.     

Spatial dispersion of adult mosquitoes (Diptera: Culicidae) in a sylvatic focus of Venezuelan equine encephalitis virus.

We studied the spatial localization of mosquitoes in sylvatic focus of Venezuelan equine encephalitis virus in western Venezuela to identify mosquito species potentially involved in the hypothesized transport of viruses out of enzootic foci. The following criteria were used to identify species with potential for virus export: (1) common in the forest and surrounding area, (2) feeding on a wide range of vertebrates; (3) long dispersal capabilities, and (4) established vectorial competence for enzootic or epizootic VEE viruses. CDC traps baited with light/CO2 were operated for four and 12-h intervals to collect mosquitoes at four stations along two forest/open area transects from September to November 1997. We collected 60,444 mosquitoes belonging to 11 genera and 34 species. The most common species were Aedes serratus (Theobald), Ae. scapularis (Rondani), Ae. fulvus (Wiedmann), Culex nigripalus Theobald, Cx, (Culex) "sp", Cx. mollis Dyar & Knab, Cx. spissipes (Theobald), Cx. pedroi Sirivanakarn and Belkin, Psorophora ferox (Humboldt), Ps. albipes (Theobald), and Ps. cingulata (F.). Very few mosquitoes were captured during the (day in the open area outside the forest, suggesting that any virus export from the forest may occur at night. The following mosquitoes seemed to be mostly restricted to the forest habitat: Ae. serratus, Ps. ferox, Ps. albipes, sabethines, Cx. spissipes, Cx. pedroi, Cx. dunni Dyar, and Ae. fulvus. The main species implicated its potential virus export were Cx. nigripalpus, Ae. scapularis, and Mansonia titillans (Walker).     

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.     

Vector competence of Peruvian mosquitoes (Diptera: Culicidae) for epizootic and enzootic strains of Venezuelan equine encephalomyelitis virus

Mosquitoes collected in the Amazon Basin, near Iquitos, Peru, were evaluated for their susceptibility to epizootic (IAB and IC) and enzootic (ID and IE) strains of Venezuelan equine encephalomyelitis (VEE) virus. After feeding on hamsters with a viremia of approximately 10(8) plaque-forming units of virus per milliliter, Culex (Melanoconion) gnomatus Sallum, Huchings, & Ferreira, Culex (Melanoconion) vomerifer Komp, and Aedes fulvus (Wiedemann) were highly susceptible to infection with all four subtypes of VEE virus (infection rates > or = 87%). Likewise, Psorophora albigenu (Peryassu) and a combination of Mansonia indubitans Dyar & Shannon and Mansonia titillans (Walker) were moderately susceptible to all four strains of VEE virus (infection rates > or = 50%). Although Psorophora cingulata (Fabricius) and Coquillettidia venezuelensis (Theobald) were susceptible to infection with each of the VEE strains, these two species were not efficient transmitters of any of the VEE strains, even after intrathoracic inoculation, indicating the presence of a salivary gland barrier in these species. In contrast to the other species tested, both Culex (Melanoconion) pedroi Sirivanakarn & Belkin and Culex (Culex) coronator Dyar & Knab were nearly refractory to each of the strains of VEE virus tested. Although many of the mosquito species found in this region were competent laboratory vectors of VEE virus, additional studies on biting behavior, mosquito population densities, and vertebrate reservoir hosts of VEE virus are needed to incriminate the principal vector species.     

The full-length nucleotide sequences of the virulent Trinidad donkey strain of Venezuelan equine encephalitis virus and its attenuated vaccine derivative, strain TC-83

Nucleotide sequence analysis of cDNA clones covering the entire genomes of Trinidad donkey (TRD) Venezuelan equine encephalitis (VEE) virus and its vaccine derivative, TC-83, has revealed 11 differences between the genomes of TC-83 virus and its parent. One nucleotide substitution and a single nucleotide deletion occurred in the 5'- and 3'-noncoding regions of the TC-83 genome, respectively. The deduced amino acid sequences of the nonstructural polypeptides of the two viruses differed only in a conservative Ser(TRD) to Thr(TC-83) substitution in nonstructural protein (nsP) three at amino acid position 260. The two silent mutations (one each in E1 and E2), one amino acid substitution in the E1 glycoprotein, and five substitutions in the E2 envelope glycoprotein of TC-83 virus were reported previously (B.J.B. Johnson, R.M. Kinney, C.L. Kost, and D.W. Trent, 1986, J. Gen. Virol. 67, 1951-1960). The genome of TRD virus was 11,444 nucleotides long with a 5'-noncoding region of 44 nucleotides. The carboxyl terminal portion of VEE nsP3 contained two peptide segments (7 and 34 amino acids long) that were repeated with high fidelity. The open reading frame of the nonstructural polyprotein was interrupted by an in-frame opal termination codon between nsP3 and nsP4, as has been reported for Sindbis, Ross River, and Middelburg viruses. The deduced amino acid sequences of the VEE TRD nsP1, nsP2, nsP3, and nsP4 polypeptides showed 60-66%, 57-58%, 35-44%, and 73-71% identity with the aligned sequences of the cognate polypeptides of Sindbis and Semliki Forest viruses, respectively. The lack of homology in the nsP3 of the viruses is due to sequence variation in the carboxyl terminal half of this polypeptide.     

Venezuelan equine encephalomyelitis virus infection in and transmission by the tick Amblyomma cajennense (Arachnida: Ixodidae)

To assess a possible role of ticks as the maintenance host for epizootic strains of Venezuelan equine encephalomyelitis (VEE) virus, laboratory experiments were conducted to determine if ticks could become infected, maintain, and transmit the virus. Larval and nymphal Amblyomma cajennense (F.) and larval Dermacentor nitens Neumann ticks were exposed to epizootic VEE virus (Trinidad donkey strain) by allowing them to feed on viremic guinea pigs (strain 13). In A. cajennense, transstadial transmission was observed from larvae to nymphs and adults. Horizontal viral transmission to a mammalian host was accomplished by nymphs. Infection rates in nymphs and adults were 2% (42/2,750) and 4% (9/244), respectively, afer ingestion of virus as larvae. Virus was detected in A. cajennense adult ticks for up to 171 d after infection in the larval stage. A cajennense, exposed as nymphs, ingested virus but did not become infected (0/164 after 10 d after taking an infective bloodmeal). No virus was detected in D. nitens 7 d after exposure. These findings suggest that A. cajennense potentially could be involved in an interepizootic maintenance cycle of epizootic VEE viral strains.     

Transmission of Venezuelan equine encephalomyelitis virus by strains of Aedes albopictus (Diptera: Culicidae) collected in North and South America

Experimental studies were undertaken to ascertain the vector potential of North American (Houston and Alsace) and South American (Sao Paulo and Santa Teresa) strains of Aedes albopictus (Skuse) for an epizootic (Trinidad donkey) strain of Venezuelan equine encephalomyelitis (VEE) virus. Infection rates were similar in all four strains of Ae. albopictus tested after ingestion of VEE virus from a viremic hamster. Virus disseminated from the midgut to the hemocoel in about 80% of infected mosquitoes, regardless of the dose ingested (10(4.6) to 10(5.7) plaque-forming units per mosquito) or the time of extrinsic incubation (7-35 d). Although all four strains of this mosquito transmitted VEE virus by bite to hamsters, transmission rates were significantly higher for the South American strains (24%, 40 of 170) than for the North American strains (5%, 9 of 165). Although VEE virus has never been isolated from Ae. albopictus, the introduction of this species into the Americas may allow it to serve as an amplification vector in areas where epizootic strains of VEE are found or introduced.     

Experimental transmission of Venezuelan equine encephalomyelitis virus by a strain of Aedes albopictus (Diptera: Culicidae) from New Orleans, Louisiana.

Experimental studies were undertaken to ascertain the vector competence of a strain of Aedes albopictus (Skuse) collected in New Orleans, LA, (Gentilly strain) for an epizootic (Trinidad donkey) strain of Venezuelan equine encephalomyelitis (VEE) virus. This strain of Ae. albopictus was significantly more susceptible to infection with VEE virus than were any of the four strains tested previously, including two from North America and two from South America. Likewise, dissemination (148 of 180) (82%) and transmission (40 of 88) (45%) rates were significantly higher in the Gentilly strain than in any of the strains previously tested. Analysis of the results of the present study along with those of a previous study with a second alphavirus, chikungunya (CHIK) virus, indicated that, although all three strains of Ae. albopictus tested were more susceptible to VEE virus than to CHIK virus, susceptibility to infection and dissemination with one alphavirus appeared to be directly related to susceptibility to infection and dissemination with the other virus and may indicate shared receptor sites for these two alphaviruses in Ae. albopictus.     

Transmission of Venezuelan equine encephalomyelitis virus by Aedes sollicitans and Aedes taeniorhynchus (Diptera: Culicidae).

Experimental studies compared the vector competence of Aedes sollicitans (Skuse) and Ae. taeniorhynchus (Wiedemann) collected on Assateague Island, Va., for an epizootic strain (Trinidad donkey) of Venezuelan equine encephalomyelitis (VEE) virus. Infection rates were significantly higher in Ae. sollicitans (101/107, 94%) than in Ae. taeniorhynchus (103/175, 59%), even though both species fed concurrently on the same infected hamsters. Similarly, dissemination and transmission rates were significantly higher in the Ae. sollicitans population tested. Although both Ae. taeniorhynchus and Ae. sollicitans are natural vectors of VEE virus, the latter species should be considered a more efficient vector of VEE epizootic strains, based on its greater susceptibility to infection and higher transmission rates.     

The differentiation of viruses in the Venezuelan equine encephalomyelitis complex by using monoclonal antibodies and lanthanide immunofluorescence analysis]

Potentialities of differentiation between Venezuelan equine encephalomyelitis (VEE) complex viruses by time-resolved fluoroimmunoassay and enzyme immunoassay were studied. For this, 4 test systems were used based on different combinations of native and labeled polyclonal antibodies to VEE virus, strain Trinidad, and monoclonal (MCA) antibody MAK 14-7 to protein EL of this virus. The maximal sensitivity and specificity was achieved in the test system formed from native MCA MAK 14-7 for sensitization of the solid phase and labeled polyclonal immunoglobulins for demonstration of the test results. This combination of antibodies allowed to differentiate the epidemic variant of VEF/Trinidad (IA) from epizootic variants of Mucambo (III), Pixuna (IV) and attenuated strain No. 230.