Valeria Carolina Colombo

In vitro isolation and infection intensity of Rickettsia parkeri in Amblyomma triste ticks from the Paraná River Delta region, Argentina.

In the present study, we report the first in vitro isolation and infection intensity of Rickettsia parkeri in Amblyomma triste ticks from Argentina. No genetic differences in the molecular targets evaluated were found between R. parkeri isolates from Argentina and those R. parkeri isolates reported in Uruguay and Brazil, both obtained from A. triste. Only a minor difference was observed when compared to R. parkeri isolated from Amblyomma maculatum from United States. Moreover, the prevalence of infection by R. parkeri in ticks collected from the vegetation in the Paraná Delta was high (20.4%). Interestingly, the distribution of R. parkeri infection intensity observed in A. triste ticks was distinctly bimodal, with approximately 60% of the infected ticks presenting high rickettsial loads (3.8×10(5)-4.5×10(7) ompA copies/tick) and the remainder with low rickettsial levels (5.6×10(1)-6.5×10(3) ompA copies/tick). This bimodality in R. parkeri infection intensity in ticks could determine differences in the severity of the disease, but also be important for the infection dynamics of this pathogen. Further research exploring the distribution of rickettsial infection levels in ticks, as well as its determinants and implications, is warranted.

Dynamics of Exposure to Rickettsia parkeri in Cattle in the Paraná River Delta, Argentina

Abstract Several cases of human rickettsiosis caused by Rickettsia parkeri were recently documented in the Paraná River delta of Argentina, where the tick vector is Amblyomma triste Koch. As cattle suffer recurrent A. triste infestations, they are at risk of becoming infected with R. parkeri. Herein we investigated the dynamics of R. parkeri and its A. triste vector in a herd of beef cattle. Cattle were followed for 18mo and samples were analyzed for the presence of antibodies against four Rickettsia species (R. parkeri, Rickettsia bellii, Rickettsia amblyommii, and Rickettsia felis) and also for the presence of rickettsial DNA. Additionally, cattle were examined for attached ticks and questing adult ticks were collected. All ticks were analyzed for the presence of rickettsial DNA. No evidence of rickettsemia was found in any cow, but the high R. parkeri infection rate documented in A. triste both questing in the study area (13.9%) and feeding on cattle (19.8%) and the identification of antibodies against R. parkeri antigen in 90% of cattle are evidence that infection is taking place. Altogether, our data suggest that A. triste ticks are capable of naturally exposing cattle to R. parkeri. However, the progress of R. parkeri infection and its impact on bovine health and production remain to be established.

Seasonality of immature stages of Ixodes loricatus (Acari: Ixodidae) in the Paraná Delta, Argentina.

In this study we analyzed seasonal trends of immature stages of Ixodes loricatus parasitizing Akodon azarae (Sigmodontinae) in a locality of the Paraná Delta, Buenos Aires, Argentina. The data encompassed two consecutive years and the analysis included the control of potential confounders using Generalized Linear Mixed Models (GLMM) with a negative binomial response. Larvae had within-year differences in abundance, but the peak months differed drastically between both sampling years, indicating that there was no consistent seasonal pattern. Regarding nymphs, a seasonal pattern was first apparent, but it vanished completely when potential confounders were considered, strongly suggesting that the association with season was spurious and caused by the confounders. Our results showed that the occurrence of immature I. loricatus in its hosts does not follow a distinct seasonal pattern, and highlight the usefulness of controlling for confounding and statistically assessing consistency between years when establishing tick seasonality.

Factors affecting patterns of Amblyomma triste (Acari: Ixodidae) parasitism in a rodent host.

Here we offer a multivariable analysis that explores associations of different factors (i.e., environmental, host parameters, presence of other ectoparasites) with the interaction of Amblyomma triste immature stages and one of its main hosts in Argentina, the rodent Akodon azarae. Monthly and for two years, we captured and sampled rodents at 16 points located at 4 different sites in the Parana River Delta region. The analyses were conducted with Generalized Linear Mixed Models with a negative binomial response (counts of larvae or nymphs). The independent variables assessed were: (a) environmental: trapping year, season, presence of cattle; type of vegetation (natural grassland or implanted forest); rodent abundance; (b) host parameters: body length; sex; body condition; blood cell counts; natural antibody titres; and (c) co-infestation with other ectoparasites: other stage of A. triste; Ixodes loricatus; lice; mites; and fleas. Two-way interaction terms deemed a priori as relevant were also included in the analysis. Larvae were affected by all environmental variables assessed and by the presence of other ectoparasites (lice, fleas and other tick species). Host factors significantly associated with larval count were sex and levels of natural antibodies. Nymphs were associated with season, presence of cattle, body condition, body length and with burdens of I. loricatus. In most cases, the direction and magnitude of the associations were context-dependent (many interaction terms were significant). The findings of greater significance and implications of our study are two. Firstly, as burdens of A. triste larvae and nymphs were greater where cattle were present, and larval tick burdens were higher in implanted forests, silvopastoral practices developing in the region may affect the population dynamics of A. triste, and consequently the eco-epidemiology of Rickettsia parkeri. Secondly, strong associations and numerous interactions with other ectoparasites suggest that co-infestations may be more important for tick dynamics than has so far been appreciated.

New host species for Leptospira borgpetersenii and Leptospira interrogans serovar Copenhageni

We investigated the presence of infection by Leptospira spp. in an assembly of Sigmodontinae rodents from the Paraná Delta, Argentina. Rodents were captured in places with natural grassland, implanted forest, with and without raising cattle and in sites prone and not prone to flooding. The DNA was amplified from cultured isolates by PCR and Leptospira spp. strains were genotyped using Multiple - Locus Variable Number Tandem Repeat Analysis (MLVA). We isolated Leptospira interrogans serovar Copenhageni from Oligoryzomys nigripes, Leptospira borgpetersenii from Scapteromys aquaticus and Leptospira interrogans serovar Icterohaemorrhagiae from Akodon azarae. The zoonotic Leptospira isolated and genotyped from O. nigripes and S. aquaticus are the first reports from these species. The geographic range of these rodent species include, in addition to Argentina, the countries of Paraguay, Uruguay and Brazil, suggesting that these rodents might be involved in the transmission of spirochetes in other regions. Human and animal health care professionals should be alert to the potential occurrence of leptospirosis in areas where these rodent species are present.

Tick host specificity: An analysis based on host phylogeny and tick ecological features using Amblyomma triste and Amblyomma tigrinum immature stages

Here we have evaluated tick host specificity with two different methodological approaches considering Amblyomma tigrinum and Amblyomma triste immatures as targets. Firstly, the Std* index was applied, which considers host phylogenetic relationships weighted by the prevalence of the parasite; followed by generalized linear models to explore associations between different host species and burdens and prevalence of larvae and nymphs, independently. The Std* index showed that A. tigrinum larvae and nymphs infest host species belonging to different orders and classes, respectively; while A. triste immatures fed on hosts that belong to different tribes, showing that both tick species have low specificity and thus, a generalist behavior. When analyzing prevalence and burdens, we found that both tick species infest some hosts more heavily compared with the rest. Even though immature stages of A. triste and A. tigrinum are generalists, the level of infestation within the range of usual hosts of these two species is uneven. This shows that a generalist behavior may result in dissimilar levels of infestation across a range of usual hosts.

First records of Myotis nigricans (Schinz, 1821) (Chiroptera, Vespertilionidae) and two new localities for three bat species in Santa Fe province, Argentina

We present the first records of Myotis nigricans (Schinz, 1821) for Santa Fe province, Argentina. Four specimens were collected in the following localities: Esperanza (Las Colonias department), Laguna Paiva (La Capital department), and Rosario (Rosario department). These records extend the distribution area of M. nigricans 380 km to the south and increase the number of bat species in Santa Fe to 23. Additionally, Esperanza and Rafaela are added as new localities for Eumops glaucinus (Wagner, 1843), Molossops temminckii (Burmeister, 1854), and Lasiurus blossevillii (Lesson & Garnot, 1826).