Mortality in immatures of the floodwater mosquito Ochlerotatus albifasciatus (Diptera: Culicidae) and effects of parasitism by Strelkovimermis spiculatus (Nematoda: Mermithidae) in Buenos Aires Province, Argentina

Life tables were constructed for six cohorts of immature stages of the floodwater mosquito Ochlerotatus albifasciatus (Macquart) in a park in Buenos Aires, highlighting the mortality attributable to the parasitic nematode, Strelkovimermis spiculatus Poinar & Camino. Two cohorts were selected to compare parasite incidence in all mosquito stages when low and high parasitism occurred. Development time of Oc. albifasciatus from first instar to adult was 7.7-10 days in the spring, 6 days in the summer, and 10.9-21.9 days in the fall. Survival was estimated as 0-1.4% in the spring, 2% in the summer and 0.2-4.4% in the fall. The highest "K" value (Killing power) occurred during a fall cohort when prevalence of the parasite was 86.9%, and the lowest in a spring cohort. Parasitism occurred during all seasons, but S. spiculatus persisted to adult only in the summer and fall, when adult mosquitoes developed from parasitized third and fourth instars larvae. The abundance of S. spiculatus differed between old and young larvae only when parasite prevalence was the highest. Although pupae and adults of Oc. albifasciatus were parasitized, no pupal mortality attributable to parasitism was recorded. The proportion of parasitized adults ranged from 14.2% and 5.7% in the two cohorts compared. Pupal wet weight and adult wing lengths did not differ between parasitized and unparasitized individuals.

Two new species of Nomimoscolex (Cestoda: Proteocephalidea, Monticelliidae) from Gymnotus carapo (Pisces: Gymnotiformes) in Argentina

Nomimoscolex guillermoi n. sp. and N. dechambrieri n. sp. are described from the gymnotiform fish Gymnotus carapo from Argentina. The new species are placed into Nomimoscolex based on the cortical position of the vitelline follicles, and medullary position of the testes, ovary, and uterus. Both species were compared to the 13 species considered valid in the genus. The combination of features distinguishing N. guillermoi from N. dechambrieri is (1) the position of the vagina to cirrus pouch (anterior or posterior vs always anterior respectively), (2) the total number of testes (41-85 vs 108-130 respectively), (3) the distribution of the vitelline follicles (arranged in dorso-lateral and ventro-lateral bands vs lateral bands respectively), (4) the length of the uteroduct (ending 58% vs 35% from posterior margin of mature proglottis respectively), and (5) the presence of gland cells in the scolex (unicellular glands in the apical region and the external margin of suckers vs the presence of unicellular glands in the apex and other grouped in a cluster medially to the suckers respectively).

Oviposition activity and seasonal pattern of a population of Aedes (Stegomyia) aegypti (L.) (Diptera: Culicidae) in subtropical Argentina

Monthly oviposition activity and the seasonal density pattern of Aedes aegypti were studied using larvitraps and ovitraps during a research carried out by the Public Health Ministry of Salta Province, in Tartagal, Aguaray and Salvador Mazza cities, in subtropical Argentina. The A. aegypti population was active in both dry and wet seasons with a peak in March, accordant with the heaviest rainfall. From May to November, the immature population level remained low, but increased in December. Ae. aegypti oviposition activity increased during the fall and summer, when the relative humidity was 60% or higher. Eggs were found in large numbers of ovitraps during all seasons but few eggs were observed in each one during winter. The occurrence and the number of eggs laid were variable when both seasons and cities were compared. The reduction of the population during the winter months was related to the low in the relative humidity of the atmosphere. Significant differences were detected between oviposition occurrences in Tartagal and Aguaray and Salvador Mazza cities, but no differences in the number of eggs were observed. Two factors characterize the seasonal distribution pattern of Ae. aegypti in subtropical Argentina, the absence of a break during winter and an oviposition activity concomitant of the high relative humidity of the atmosphere.

Arthropod and filarioid parasites associated with wild rodents in the northeast marshes of Buenos Aires, Argentina

During 1995, 16 species of arthropods and 2 species of filarioids, totaling 1 287 specimens were collected from 64 wild rodents captured in the Hudson Natural Reserve, Buenos Aires, Argentina. Infestation parameters and indexes were analyzed. Host specific richness was S = 6, diversity H = 1.48, and relative density RDI = 40%. High values of parasite species richness and diversity were found on Oligoryzomys delticola (S = 9; H = 1.40), Oxymycterus rufus (S = 9; H = 1.37), and Oligoryzomys flavescens (S = 9; H = 1.28), followed by Scapteromys aquaticus (S = 6; H = 0.17), and Akodon azarae (S = 4; H = 1.20). Deltamys kempi was infested only by Androlaelaps rotundus. O. delticola and O. flavescens showed the highest similarity index (O = 74.19%), followed by O. flavescens with S. aquaticus, as a result of historical processes and shared microhabitats. Considering arthropods-filarioids associations, significant affinity was observed in Litomosoides bonaerensis with Hoplopleura travassosi, Laelaps paulistanensis, and Gigantolaelaps wolffsohni.

Prevalence of infection with hantavirus in rodent populations of central Argentina

We studied hantavirus seroprevalence and virus variability in rodent populations in Diego Gaynor, northwest of Buenos Aires province, Argentina. Rodent samplings were conducted in railroads and cropfield borders in March and July 1999, September and December 2000, and March 2001. Antibody detection was performed by an enzyme link immunosorbent assay (ELISA), using the recombinant nucleoprotein of Andes (AND) virus as antigen. Tissue samples were taken from positive antibody individuals in order to confirm the presence of hantavirus genomic material and to identify virus genotypes. Akodon azarae was the most abundant species, followed by Oligoryzomys flavescens, while Calomys laucha and C. musculinus were rarely caught. We found a rate of seroprevalence of 9.3% for a total sample of 291 A. azarae and 13.5% for 37 O. flavescens. After molecular analyses of hantavirus, we confirmed the presence of hantavirus genomic material in 16 individuals with ELISA (+) results and two individuals with ELISA (-). Four amplimers for each species were sequenced and compared to the corresponding sequences of representative hantaviruses. We identified the AND Cent Lec from three O. flavescens, and the Pergamino virus from four A. azarae and from one O. flavescens. A. azarae males had higher seroprevalence than females, and heavier individuals showed higher seroprevalence than lighter ones. We did not find seroprevalence differences according to sex in O. flavescens, although this result may have been produced by the low sample size. The lowest seroprevalence was found in a period of high rodent density, when juveniles prevailed in the population. We found higher seroprevalences than those detected in previous studies for other localities of central Argentina where cases of hantavirus pulmonary syndrome (HPS) have been reported. The presence of AND Cent Lec virus in rodent populations of the study area, which is responsible of HPS cases in central Argentina, suggests that human populations are at risk of HPS disease, although there were not reported cases of this disease until today.

First report of Lymnaea columella Say, 1817 (Pulmonata: Lymnaeidae) naturally infected with Fasciola hepatica (Linnaeus,1758) (Trematoda: Digenea) in Argentina

We report the first evidence of natural infection of Lymnaea columella with Fasciola hepatica in Argentina. A sample of 601 snails was collected in May 2003 in northeastern Corrientes, a province bounded on the north by Paraguay, on the east by Brazil and on the southeast by Uruguay. Among 500 examined snails, 44 (8.8%) were exclusively infected with F. hepatica. Parasite identification was based on morphological features of cercariae from snails, and of eggs and adult flukes from Wistar rats. We discuss the events suggesting that an enzootic transmission cycle of F. hepatica has been recently established in northeastern Corrientes.

Ecological characteristics of Triatoma patagonica at the Southern limit of its distribution (Chubut, Argentina)

This study aimed at identifying the ecological characteristics of Triatoma patagonica Del Ponte 1929 (Hemiptera: Reduviidae) and evaluating the epidemiological importance of this species at its southernmost distribution limit. We carried out two surveys in the Province of Chubut, in summer and in spring, 1998. In each survey, we interviewed local health care agents for triatomine recognition and reports of the bugs, followed by entomological searches in houses and peridomestic and silvatic biotopes. The presence of T. patagonica was confirmed in two of the five localities indicated by interview. In agreement with previous studies, all these positive localities were east of the 11°C isotherm, within the Monte phytogeographic province. Triatomine abundance and infestation levels (in peridomiciles and peridomestic biotopes) were higher in summer than in spring, possibly reflecting adverse environmental conditions such as flood and cold winter weather. In the silvatic environment, we found three adult bugs under rocks in summer. In peridomestic sites bugs were only found associated with chickens, which were also the only blood meal source identified. Infection by Trypanosoma cruzi was not detected. We conclude that T. patagonica at its southernmost distribution limit does not represent a risk to public health due to its low abundance, lack of association with humans, and absence of T. cruzi infection.

Classification of immature mosquito species according to characteristics of the larval habitat in the subtropical province of Chaco, Argentina

To classify mosquito species based on common features of their habitats, samples were obtained fortnightly between June 2001-October 2003 in the subtropical province of Chaco, Argentina. Data on the type of larval habitat, nature of the habitat (artificial or natural), size, depth, location related to sunlight, distance to the neighbouring houses, type of substrate, organic material, vegetation and algae type and their presence were collected. Data on the permanence, temperature, pH, turbidity, colour, odour and movement of the larval habitat's water were also collected. From the cluster analysis, three groups of species associated by their degree of habitat similarity were obtained and are listed below. Group 1 consisted of Aedes aegypti. Group 2 consisted of Culex imitator, Culex davisi, Wyeomyia muehlensi and Toxorhynchites haemorrhoidalis separatus. Within group 3, two subgroups are distinguished: A (Psorophora ferox, Psorophora cyanescens, Psorophora varinervis, Psorophora confinnis, Psorophora cingulata, Ochlerotatus hastatus-oligopistus, Ochlerotatus serratus, Ochlerotatus scapularis, Culex intrincatus, Culex quinquefasciatus, Culex pilosus, Ochlerotatus albifasciatus, Culex bidens) and B (Culex maxi, Culex eduardoi, Culex chidesteri, Uranotaenia lowii, Uranotaenia pulcherrima, Anopheles neomaculipalpus, Anopheles triannulatus, Anopheles albitarsis, Uranotaenia apicalis, Mansonia humeralis and Aedeomyia squamipennis). Principal component analysis indicates that the size of the larval habitats and the presence of aquatic vegetation are the main characteristics that explain the variation among different species. In contrast, water permanence is second in importance. Water temperature, pH and the type of larval habitat are less important in explaining the clustering of species.

Potential sources of Triatoma infestans reinfesting peridomiciles identified by morphological characterization in Los Llanos, La Rioja, Argentina

The presence of Triatoma infestans in habitats treated with insecticides constitutes a frequent problem in endemic areas. Basing our study on the hypothesis that descendants of a residual population should be more similar to the pre-treatment population than to any other, we compared the indications of two quantitative morphological approaches. This study seeks to find the origin of 247 T. infestans from three populations found in two chicken coops and a goat corral after treatment with insecticides. The results obtained by quantitative morphology suggest that the T. infestans found between three-34 months after the application of insecticides formed mixed populations with insects derived from residual foci and neighbouring habitats. Our analyses also showed the presence of a phenotype which does not resemble neither the pre-treatment phenotype nor the one from neighbouring populations, suggesting the presence of a particular post-treatment phenotype. The heads size showed some variations in males from different populations and remained unchanged in females, which reinforces the hypothesis of an intraspecific competition for food with priority for females. This article presents, for the first time, the combined analysis of geometric morphometry of heads and antennal phenotypes to identify the composition of reinfesting populations.

Performance and hormonal profile in broiler chickens fed with different energy levels during post restriction period

The aim of this work was to investigate the influence of diet energy level on performance and hormonal profiles of broilers during post restriction period. It was a split-plot experiment, and the main treatments were in a 2x2 factorial scheme. Birds were fed restricted to 30% of the ad libitum intake, from 7 to 14 days of age. After the restriction period, birds were fed ad libitum with diets containing low (2,900 kcal ME/kg) or high (3,200 kcal ME/kg) energy until 49 days of age. Broilers fed with high energy ration showed lower feed intake and better feed conversion and decreased carcass protein; however, abdominal fat pad, and total carcass fat were not affected by ration energy levels or feeding program. Neither diet energy level nor feed restriction program changed body weight at 49 days. The profile of insulin-like growth factor-1 (IGF-1) was reduced during the feed restriction period, but increased at refeeding period. Feeding program and ration energy level did not affect T3, T4 and growth hormone serum concentrations. Feed restriction at 30% of ad libitum intake is not enough to promote changes on carcass quality, related to fat deposition, and on metabolic hormone levels, except IGF-1 seric level that has rapid increase after feed restriction.

Exserohilum rostratum patógeno de Caryota mitis en Argentina

Caryota mitis Loureiro (Arecaceae), es cultivada en Argentina como planta ornamental con fines comerciales. En el año 2003, muestras procedentes de la localidad de Castelli, provincia del Chaco, Argentina, presentaban atizonamiento de los ápices de las hojas, deteriorándolas considerablemente. Mediante métodos comunes de laboratorio se aisló un hongo Dematiaceae relacionado con los síntomas observados. Con base en las características culturales, morfométricas, pruebas de patogenicidad con resultados positivos, el agente causal fue identificado como Exserohilum rostratum (Drechsler) Leonard & Suggs. Esta es la primera información de E. rostratum afectando a C. mitis en Argentina.

Main diseases of pejerrey (Odontesthes bonariensis) in central Argentina

Argentina's central region includes an important area covered by shallow pampean lakes and dams. In these environments, fishing of pejerrey Odontesthes bonariensis Valenciennes, 1835 (Pisces, Atherinopsidae), the most important fresh-water fish of the country, is a relevant social activity and also a considerable economic resource. The main diseases found in this species were studied from 1992 to 2003 in the provinces of Córdoba, La Rioja and Santa Fe (30º and 35º S, 61º and 67º W). Most cases were registered in high temperature months. Lernaea sp and Aeromonas hydrophila were the etiological agents most frequently found. The trophic characteristics of the aquatic environments enhanced disease processes and caused massive death of O. bonariensis, due to complex hydrochemical interactions.

Health management practices and disease prevalence in dairy sheep systems in Argentina

A cross-sectional survey of 19 dairy sheep farms in Argentina was carried out with the purpose to know farm management, health practices, and occurrence and mortality of diseases. The survey comprised 40% of all sheep milking farms in Argentina. A questionnaire was conducted by way of personal interviews with sheep owners during farm visits. The proportions of farms reporting routine vaccination for clostridial diseases, contagious ecthyma, pneumonia and mineral and vitamin parenteral administration were 63%, 47.3%, 16.6% and 42.1% respectively. Regular treatment against lice was used in 37.5% of the farms, and 89.5% o the farmers treated against gastrointestinal nematodes (GIN). The mean number of GIN drenches per farm was 2.26±1.78 annually. In 68.4% of the milking flocks the California Mastitis Test was regularly done and 55.6% of the farmer managers had sampled their flocks once a year for Brucella ovis antibodies. During the pre-mating period respectively 68.4% and 50% of farmers clinically examined their rams and ewe for general health and teeth condition. The udders of ewes were frequently inspected at the start of each milking period. The most important parasite problems noticed were GIN (reported by 57.9% of farmers), lice (57.9%) and scabies (10.5%) and the most frequent infectious diseases were ecthyma (73.7%), pneumonia and other respiratory problems (57.9%), clinical mastitis (55.6%), clostridial diseases (36.9%) and foot lameness (35.2%). Photosensitivity (47.4%) and ruminal acidosis (42.1%) were reported as other frequent toxic or metabolic disorders. Owners mentioned that the mean lifespan or milk productive time per ewe was 4.5±1.4 years. Perinatal lamb mortality was 8.5% and the total flock mortality rates, above the first 24 h of life was 6.9%. The high rates of lamb mortality during the pre-weaning (10.3%) and post-weaning (5.9%) periods indicate that this problem, as well as the most prevalent diseases, should be the subject of further studies.

Impact of ivermectin-resistant gastrointestinal nematodes in feedlot cattle in Argentina

The aim was to evaluate for 75 days the impact on production of the remaining burden of ivermectin (IVM)-resistant parasites in naturally infected feedlot calves. The herds came from tick-infested areas of cattle breeding where the systematic use of IVM to control tick increases the gastrointestinal parasites resistant to this drug. This investigation was carried out in two commercial feedlots in Buenos Aires province. In feedlot A, two groups of 35 animal each received IVM 1% and the other received ricobendazole (RBZ) 10% respectively. The same was done in feedlot B. On day 0, two groups of 35 animals were made in feedlots A and B. Fecal samples were taken on days 0, 22, 54 and 75 pos-treatment (PT), and body weight was registered, from each animal. Fecal samples were processed for individual count of eggs per gram (EPG) and pooled fecal culture was carried out for identification of the parasite genus in each sampling. Fecal egg count reduction test (FECR) was calculated on day 22 PT. The study design used was a totally randomized block, with commercial feedlot and sex as block variables. For data analysis, a mixed model of the SAS statistical program was used. The FECR average on day 22 was 28.4% in the IVM group, and 94,2 % in the RBZ group . From this date on, significant differences in EPG were kept until day 54. EPG counts were only equal near the end of the trial, on day 75 (p=0.16). In both commercial feedlots, especially in the IVM group, Cooperia spp. was the most prevalent parasite in the fecal cultures. Significant differences in weight (P<0.01) on post-treatment day 75 was found between the average weight in the RBZ and the IVM group (246 vs. 238 kg respectively), what means a difference of 8.3% in gains. The importance for production in the antiparasite failure treatment in commercial feedlots was demonstrated, and the need of pos-treatment controls to evaluate the efficacy of the antiparasitic administered is emphasized.

Late-acting self-incompatibility in Capparis retusa (Capparaceae), a species of Chaco woodland in NE Argentina

The reproductive biology of Capparis retusa was studied by means of controlled pollination experiments and fluorescence microscopy observations of post-pollination events. Self-pollinated flowers mostly failed to form fruits despite the fact that self-pollen tubes grew to the ovary and penetrated ovules within 24 h. Since embryo development to globular stage was observed in some self-fertilized ovules it was concluded that control of self-fertilization in this species occurs by some kind of post-zygotic mechanism.