The extent of infectious SARS-CoV-2 shedding in an Argentinean cohort.

BACKGROUND: To analyze the infectious extent of severe acute respiratory syndrome coronavirus 2 (SARS-COV-2) in different settings where prevention strategies are critical to limit infection spread, we evaluated SARS-COV-2 viability to guide public health policies regarding isolation criteria and infection control. METHODS: We attempted viral isolation in 82 nasopharyngeal swabs from 72 patients with confirmed SARS-COV-2 infection. Study population was divided into four groups: (i) Patients during the first week of symptoms; (ii) Patients with prolonged positive PCR; (iii) Healthcare workers from a hospital participating of an outbreak investigation, with SARS-COV-2 infection confirmed by reverse transcriptase polymerase chain reaction (RT-PCR) and (iv) Recipients of convalescent immune plasma (CIP).Vero Cl76 cell-line (ATCC CRL-587) was used in assays for virus isolation. Plasma samples of CIP recipients were also tested with plaque-reduction neutralization test. RESULTS: We obtained infectious SARS-COV-2 isolates from 15/84 nasopharyngeal swabs. The virus could not be isolated from upper respiratory tract samples collected 10-day after onset of symptoms (AOS) in patients with mild-moderate disease. CONCLUSION: The knowledge of the extent of SARS-CoV-2 infectivity AOS is relevant for effective prevention measures. This allows to discuss criteria for end isolation despite persistence of positive PCR and improve timing for hospital discharge with consequent availability of critical beds.

First Detection of Madariaga virus in Mosquitoes Collected in a Wild Environment of Northeastern Argentina.

Madariaga virus (MADV), previously known as South American eastern equine encephalitis virus (SA EEEV; family Togaviridae, genus Alphavirus), is a mosquito-borne virus associated mainly with equine disease. In 2010, the first human outbreak by MADV was reported in Central America, but the mosquito vectors and vertebrate hosts involved in the outbreak were not identified. In Argentina, the first epizootic of MADV was in 1930, and since then, several epizootics by MADV have been reported. However, the potential vectors and hosts involved in the transmission cycle remain unknown. In the present study, MADV was detected in Culex (Culex) spp. mosquitoes and the phylogenetic analysis showed that the MADV fragment amplified grouped with the lineage/subtype III of the SA EEEV complex. Our results provide information about the natural infection with MADV in mosquitoes collected in a wild environment of Argentina and its genetic relatedness.

Genomic Characterization and Seroprevalence Studies on Alphaviruses in Uruguay.

Alphaviruses (Togaviridae) are arboviruses frequently associated with emerging infectious diseases. In this study, we aimed to investigate the presence of alphaviruses in Uruguay by detecting the viral genome in mosquitoes and neutralizing antibodies in equines. A total of 3,575 mosquitoes were analyzed for alphavirus genome detection. Serologic studies were performed on 425 horse sera by plaque reduction neutralization test (PRNT80) against Venezuelan equine encephalitis virus (VEEV) subtype IAB, Pixuna virus (PIXV), Rio Negro virus (RNV), western equine encephalitis virus (WEEV), and Madariaga virus (MADV). Mosquitoes belonging to six genera were captured and 82.9% were identified as Culex pipiens. Two Cx. pipiens pools collected in Fray Bentos and Las Toscas localities were alphavirus positive, and phylogenetic analyses showed that the sequences grouped into two different clusters: the lineage I of eastern equine encephalitis virus and RNV (VEEV complex), respectively. Plaque reduction neutralization test assays showed antibodies against strains of the VEEV complex, MADV, and WEEV. Rio Negro virus was the most geographically widespread virus, showing higher seroprevalences (up to 20%). Seroprevalences against VEEV IAB ranged between 4.6% and 13%; antibodies against PIXV, WEEV, and MADV were less frequent (3-4%). In conclusion, RNV exhibited the highest seroprevalence in horses, a wide geographical distribution, and viral genome was detected in Cx. pipiens mosquitoes. Madariaga virus had a low seroprevalence in equines, but an epizootic lineage typical of North America was detected in Cx. pipiens mosquitoes. Taken together, our results show that alphaviruses are present in Uruguay with variable occurrence and geographical distribution being a potential threat for human and equine health.

Tissue tropism of Saint Louis encephalitis virus: Histopathology triggered by epidemic and non-epidemic strains isolated in Argentina.

Saint Louis encephalitis virus (SLEV) reemerged in South America, and caused encephalitis outbreaks at the beginning of the 21st century. To enhance our knowledge about SLEV virulence, we performed comparative pathogenesis studies in Swiss albino mice inoculated with two different variants, the epidemic strain CbaAr-4005 and the non-epidemic strain CorAn-9275. Only the infection of mice with SLEV strain CbaAr-4005 resulted in high viremia, invasion of peripheral tissues including the lungs, kidney, and spleen, and viral neuroinvasion. This was associated with inflammatory pathology in the lungs, spleen, and brain as well as morbidity and mortality. In contrast, neither signs of desease nor viral replication were observed in mice infected with strain CorAn-9275. Interestingly, important loss of B cells and development of altered germinal centers (GC) were detected in the spleen of mice infected with strain CbaAr-4005, whereas mice infected with SLEV CorAn-9275 developed prominent GC with conserved follicular architecture, and neutralizing antibodies.

Activity Patterns of St. Louis Encephalitis and West Nile Viruses in Free Ranging Birds during a Human Encephalitis Outbreak in Argentina.

St. Louis encephalitis virus (SLEV) (Flavivirus) is a reemerging arbovirus in the southern cone of South America. In 2005, an outbreak of SLEV in central Argentina resulted in 47 human cases with 9 deaths. In Argentina, the ecology of SLEV is poorly understood. Because certain birds are the primary amplifiers in North America, we hypothesized that birds amplify SLEV in Argentina as well. We compared avian SLEV seroprevalence in a variety of ecosystems in and around Córdoba city from 2004 (before the epidemic) and 2005 (during the epidemic). We also explored spatial patterns to better understand the local ecology of SLEV transmission. Because West Nile virus (WNV) was also detected in Argentina in 2005, all analyses were also conducted for WNV. A total of 980 birds were sampled for detection of SLEV and WNV neutralizing antibodies. SLEV seroprevalence in birds increased 11-fold from 2004 to 2005. Our study demonstrated that a high proportion (99.3%) of local birds were susceptible to SLEV infection immediately prior to the 2005 outbreak, indicating that the vertebrate host population was primed to amplify SLEV. SLEV was found distributed in a variety of environments throughout the city of Córdoba. However, the force of viral transmission varied among sites. Fine scale differences in populations of vectors and vertebrate hosts would explain this variation. In summary, we showed that in 2005, both SLEV and to a lesser extent WNV circulated in the avian population. Eared Dove, Picui Ground-Dove and Great Kiskadee are strong candidates to amplify SLEV because of their exposure to the pathogen at the population level, and their widespread abundance. For the same reasons, Rufous Hornero may be an important maintenance host for WNV in central Argentina. Competence studies and vector feeding studies are needed to confirm these relationships.

Transmission of endemic St Louis encephalitis virus strains by local Culex quinquefasciatus populations in Cordoba, Argentina.

BACKGROUND: St Louis encephalitis virus (SLEV) is a re-emerging human pathogen widely distributed in the American continent. Although it is not fully understood, the SLEV transmission network may involve Culex quinquefasciatus mosquitoes as vectors and Columbidae species as hosts. METHODS: To calculate infection rates, we inoculated Cx. quinquefasciatus mosquitoes from Córdoba, Argentina by feeding them on viremic chicks. RESULTS: We observed differences in infection rate among the viral strains, the highest rate (78/87 mosquitoes, 90.8%) being seen in strain 78V-6507. After re-feeding on susceptible chicks, mosquitoes were able to transmit the virus. CONCLUSION: Our findings suggest that Cx. quinquefasciatus populations are susceptible to and able to transmit different SLEV strains.

Seroprevalence of St. Louis encephalitis virus and West Nile virus (Flavivirus, Flaviviridae) in horses, Uruguay.

St. Louis encephalitis virus (SLEV) and West Nile virus (WNV) belong to the Japanese encephalitis antigenic complex (Flavivirus genus, Flaviviridae family). They show antigenic close relationships and share many similarities in their ecology. Both are responsible for serious human diseases. The aim of this study was to investigate the presence of neutralizing antibodies to these viruses in horses from Uruguay. To do this, 425 horse sera were collected in 2007 and analyzed by plaque reduction neutralization tests. As a result, 205 sera (48.2%) were found positive for SLEV, with titers ranging between 10 and 80. Two sera remained inconclusive, since they showed low titers to WNV and SLEV (10 and 20), not allowing us to demonstrate activity of WNV in our territory. This is the first report of circulation of SLEV in horses in Uruguay.

Serological detection of St. Louis encephalitis virus and West Nile virus in equines from Santa Fe, Argentina.

St. Louis encephalitis virus (SLEV) and West Nile virus (WNV) present ecological and antigenic similarities and are responsible for serious human diseases. In addition, WNV is a significant pathogen in terms of equine health. The purpose of our study was to analyse the seroprevalence of SLEV and WNV in equine sera collected in Santa Fe Province, Argentina. The seroprevalence determined using the plaque reduction neutralisation test was 12.2% for SLEV, 16.2% for WNV and 48.6% for a combination of both viruses. These results provide evidence of the co-circulation of SLEV and WNV in equines in Santa Fe.

Serological detection of St. Louis encephalitis virus and West Nile virus in equines from Santa Fe, Argentina

St. Louis encephalitis virus (SLEV) and West Nile virus (WNV) present ecological and antigenic similarities and are responsible for serious human diseases. In addition, WNV is a significant pathogen in terms of equine health. The purpose of our study was to analyse the seroprevalence of SLEV and WNV in equine sera collected in Santa Fe Province, Argentina. The seroprevalence determined using the plaque reduction neutralisation test was 12.2% for SLEV, 16.2% for WNV and 48.6% for a combination of both viruses. These results provide evidence of the co-circulation of SLEV and WNV in equines in Santa Fe.

Silent circulation of St. Louis encephalitis virus prior to an encephalitis outbreak in Cordoba, Argentina (2005).

St. Louis encephalitis virus is a complex zoonoses. In 2005, 47 laboratory-confirmed and probable clinical cases of SLEV infection were reported in Córdoba, Argentina. Although the causes of 2005 outbreak remain unknown, they might be related not only to virological factors, but also to ecological and environmental conditions. We hypothesized that one of the factors for SLE reemergence in Córdoba, Argentina, was the introduction of a new SLEV genotype (SLEV genotype III), with no previous activity in the area. In order to evaluate this hypothesis we carried out a molecular characterization of SLEV detections from mosquitoes collected between 2001 and 2004 in Córdoba city. A total of 315 mosquito pools (11,002 individuals) including 12 mosquitoes species were analyzed. Overall, 20 pools (8 mosquitoes species) were positive for SLEV. During this study, genotypes II, V and VII were detected. No mosquito pool infected with genotype III was detected before the 2005 outbreak. Genotype V was found every year and in the 8 sampled sites. Genotypes II and VII showed limited temporal and spatial activities. We cannot dismiss the association of genotype II and V as etiological agents during the outbreak. However, the silent circulation of other SLEV strains in Córdoba city before the 2005 outbreak suggests that the introduction of genotype III was an important factor associated to this event. Not mutually exclusive, other factors such as changes in avian hosts and mosquitoes vectors communities, driven by climatic and environmental modifications, should also be taken into consideration in further studies.

First detection of Rio Negro virus (Venezuelan equine encephalitis complex subtype VI) in Córdoba, Argentina.

Rio Negro virus (RNV) (Venezuelan equine encephalitis subtype VI) circulates only in Argentina; in northern provinces, isolates have been obtained from mosquitoes and rodents since 1980 and have been associated with acute febrile illness in humans. However, no studies of RNV have been performed in the central area of the country. We carried out molecular and serological detection of RNV in Córdoba, a province of the central part of the country, in mosquitoes and humans, respectively. One mosquito pool tested positive for alphavirus RNA by reverse transcriptase-nested polymerase chain reaction (RT-nested PCR). Subsequent sequencing determined that this alphavirus grouped with RNV. Serological studies detected antibodies to RNV in one human serum sample, which was obtained during the same period that RNV was detected using the aforementioned molecular methods. This is the first report of RNV circulation in the central area of Argentina, indicating an expansion of its original distribution. These results highlight the importance of strengthening surveillance procedures in endemic areas, as well as in new regions where RNV may emerge.

First detection of Rio Negro virus (Venezuelan equine encephalitis complex subtype VI) in Córdoba, Argentina

Rio Negro virus (RNV) (Venezuelan equine encephalitis subtype VI) circulates only in Argentina; in northern provinces, isolates have been obtained from mosquitoes and rodents since 1980 and have been associated with acute febrile illness in humans. However, no studies of RNV have been performed in the central area of the country. We carried out molecular and serological detection of RNV in Córdoba, a province of the central part of the country, in mosquitoes and humans, respectively. One mosquito pool tested positive for alphavirus RNA by reverse transcriptase-nested polymerase chain reaction (RT-nested PCR). Subsequent sequencing determined that this alphavirus grouped with RNV. Serological studies detected antibodies to RNV in one human serum sample, which was obtained during the same period that RNV was detected using the aforementioned molecular methods. This is the first report of RNV circulation in the central area of Argentina, indicating an expansion of its original distribution. These results highlight the importance of strengthening surveillance procedures in endemic areas, as well as in new regions where RNV may emerge.

Comparison of argentinean saint louis encephalitis virus non-epidemic and epidemic strain infections in an avian model.

St. Louis encephalitis virus (SLEV, Flavivirus, Flaviviridae) is an emerging mosquito-borne pathogen in South America, with human SLEV encephalitis cases reported in Argentina and Brazil. Genotype III strains of SLEV were isolated from Culex quinquefasciatus mosquitoes in Cordoba, Argentina in 2005, during the largest SLEV outbreak ever reported in South America. The present study tested the hypothesis that the recent, epidemic SLEV strain exhibits greater virulence in birds as compared with a non-epidemic genotype III strain isolated from mosquitoes in Santa Fe Province 27 years earlier. The observed differences in infection parameters between adult House sparrows (Passer domesticus) that were needle-inoculated with either the epidemic or historic SLEV strain were not statistically significant. However, only the House sparrows that were infected with the epidemic strain achieved infectious-level viremia titers sufficient to infect Cx. spp. mosquitoes vectors. Furthermore, the vertebrate reservoir competence index values indicated an approximately 3-fold increase in amplification potential of House sparrows infected with the epidemic strain when pre-existing flavivirus-reactive antibodies were present, suggesting the possibility that antibody-dependent enhancement may increase the risk of avian-amplified transmission of SLEV in South America.

Vertical transmission of St. Louis encephalitis virus in Culex quinquefasciatus (Diptera: Culicidae) in Córdoba, Argentina.

Arbovirus vector transmission is interrupted when vector abundance decreases or disappears in temperate regions during the winter season. Although the primary overwintering mechanism for many arboviruses in nature remains unknown, vertical transmission is one potential mechanism. Vertical transmission functions as an overwintering mechanism for St. Louis encephalitis virus (SLEV) in temperate areas of Argentina, where SLEV is endemic. The aim of this project was to detect vertical transmission of SLEV in Culex quinquefasciatus mosquitoes. Under laboratory conditions, SLEV vertical transmission (3.4 minimum infection rates) was detected in larvae (1:256) and adults F1 (1:406). There were no positive larvae for SLEV among over 2011 analyzed individuals collected in nature. This is the first study to confirm experimental vertical transmission of SLEV in Cx. quinquefasciatus populations from Argentina, though additional overwintering mechanisms (e.g., nontraditional vectors such as ticks and nondiapausing female mosquitoes) should be considered.

Enzootic activity of pixuna and Rio Negro viruses (Venezuelan equine encephalitis complex) in a neotropical region of Argentina.

Venezuelan Equine Encephalitis complex viruses cause epidemics and epizootics periodically in some regions of the Americas. In Argentina, only enzootic Rio Negro virus (AG80-663) (RNV) has been isolated. To survey and identify activity of viruses that belong to Venezuelan Equine Encephalitis complex in a template region of the country, a generic Alphavirus RT-Nested PCR was performed in 99 mosquito pools collected in Chaco province. Five pools were positive, and amplicons were sequenced: four of them clustered with RNV(AG80-663) and one with Pixuna virus. This is the first report of the circulation of Pixuna virus in Argentina, and it confirms enzootic and endemic activity of RNV(AG80-663) in neotropical regions of this country.

Infection by Bunyamwera virus (Orthobunyavirus) in free ranging birds of Cordoba city (Argentina).

Infection by Bunyamwera virus (BUNV) species (Family Bunyaviridae, Genus Orthobunyavirus) has been detected in ewes, goats, cows, horses and humans all the way through America. However, there are no evidences of such infection in birds. To detect BUNV (CbaAr-426) infection in free ranging birds, a serological survey was carried out in Córdoba city between 2004 and 2005. Birds of 13 families presented neutralizing antibodies against BUNV (CbaAr-426), showing an increase in the seroprevalence from 6.6% to 13.8% between 2004 and 2005, respectively. Seroconversion for BUNV (CbaAr-426) was detected in Rufus hornero (Furnarius rufus) in January-February of 2005. This is the first evidence of natural infection by BUNV (CbaAr-426) in free ranging birds. The seroconversion level demonstrated active circulation of BUNV (CbaAr 426) in Córdoba city.

Infection by UNA virus (Alphavirus; Togaviridae) and risk factor analysis in black howler monkeys (Alouatta caraya) from Paraguay and Argentina.

A neutralizing antibody (NTAb) survey on UNA and Mayaro viruses in black howler monkeys (Aloutta caraya) from subtropical regions of Argentina and Paraguay was carried out. Risk factors for infection in monkeys were analyzed. No positive sera for Mayaro virus were detected. A prevalence of 73% (61/84) of NTAb against UNAV was detected with titers ranging from 20 to 1280. According to the statistical analysis performed, the monkey's age was a significant risk factor, but not the origin or sex. This is the first report of Alouatta caraya infection by UNAV and the first record of its activity in Paraguay.

Genotype III Saint Louis encephalitis virus outbreak, Argentina, 2005.

Twenty-six years after it was last detected, Saint Louis encephalitis virus (SLEV) genotype III reemerged in 2005 in C6rdoba, Argentina, where it caused an outbreak. Two genotype III SLEV strains were isolated from Culex quinquefasciatus. A 71.43% prevalence for neutralizing antibodies was found in domestic fowl in the homestead of a patient with encephalitis.

UNA virus: first report of human infection in Argentina.

Una virus (UNAV), Togaviridae family, is widely distributed in South America, where infections have been detected in mosquitoes and vertebrate hosts (humans, birds and horses). We analyzed human sera from Córdoba inhabitants aged 44 to 89 years and using a neutralization test, we found a prevalence of UNAV antibodies of 3.8% (3/79). The low titers detected suggest past infections probably acquired in rural areas of the Province of Córdoba (central Argentina). None sera were found positive for MAYV neutralizing antibodies. This is the first report of human infections by UNAV in Argentina.

UNA virus: first report of human infection in Argentina

Una virus (UNAV), Togaviridae family, is widely distributed in South America, where infections have been detected in mosquitoes and vertebrate hosts (humans, birds and horses). We analyzed human sera from Córdoba inhabitants aged 44 to 89 years and using a neutralization test, we found a prevalence of UNAV antibodies of 3.8 percent (3/79). The low titers detected suggest past infections probably acquired in rural areas of the Province of Córdoba (central Argentina). None sera were found positive for MAYV neutralizing antibodies. This is the first report of human infections by UNAV in Argentina