Silvina Fernández - Academia.edu (original) (raw)

Books by Silvina Fernández

The ability of two isolates of the nematode-trapping fungus Duddingtonia flagrans to reduce the n... more The ability of two isolates of the nematode-trapping fungus Duddingtonia flagrans to reduce the numbers of gastrointestinal nematode larvae on herbage was tested in three plot studies. Artificially prepared cow pats containing Ostertagia ostertagi eggs, with and without fungal spores, were deposited on pasture plots two or three times during the grazing season in 1995, 1996 and 1997. The herbage around each pat was sampled fortnightly over a period of 2 months and the number of infective larvae was recorded. At the end of the sampling period, the remainder of the faecal pats was collected to determine the wet weight, dry weight, and content of organic matter. The infective larvae remaining in the pats were extracted. Faecal cultures showed that both fungal isolates significantly reduced the number of infective larvae. Significantly fewer larvae were recovered from herbage surrounding fungus-treated pats compared with control pats in all three experiments, reflecting the ability of the fungus to destroy free-living larval stages in the faecal pat environment. After 8 weeks on pasture there were no differences between control and fungus-treated pats with respect to wet weight, dry weight, and organic matter content. This indicates that the degradation of faeces was not negatively affected by the presence of the fungus.

The capacity of microfungi known as ‘nematophagous fungi’ to reduce the numbers of parasitic nema... more The capacity of microfungi known as ‘nematophagous fungi’ to reduce the numbers of parasitic nematodes is anything but a new subject. However, the research into the actual development of these fungi for biological control purposes and their practical application in veterinary medicine has made inroads only during the last two decades.
This chapter intends to shed light on those inroads, focusing on the application of biological control of parasites of veterinary importance. Examples of parasite-destroying fungi other than nematophagous ones are also mentioned in the chapter.
The four functional categories of nematophagous fungi are nematode-trapping, endoparasitic, egg- and cyst-parasitic fungi, and toxin-producing fungi. Although species of all categories have shown capabilities to act as biological control agents at different levels, the first group has been more extensively studied for that purpose to this date. However, the field for using the second and third groups remains wide open. While the last category is briefly mentioned and exemplified, this chapter focuses on the first three categories, including their description, biology, and behaviour in the environment.
The research into using nematophagous fungi to control parasitic nematodes of veterinary importance has not only elucidated issues such as which fungal species are the most promising candidates and their individual nematode suppressive effect under controlled conditions, but has also raised problematic questions ranging from the use of the fungi in different geographical and climate regions to the formulation, commercialisation and regulatory aspects of their use. All these and the future perspectives of this exciting field of knowledge will be covered in this chapter.

Papers by Silvina Fernández

Pathogens

The purpose of using nematophagous fungi as biological control agents of gastrointestinal nematod... more The purpose of using nematophagous fungi as biological control agents of gastrointestinal nematodes of livestock is to reduce the build-up of infective larvae on pasture and thus avoid clinical and subclinical disease. As the interaction of fungus-larval stages takes place in the environment, it is crucial to know how useful the fungal agents are throughout the seasons in areas where livestock graze all year-round. This study was designed to determine the predatory ability of the nematophagous fungus Duddingtonia flagrans against gastrointestinal nematodes of cattle during four experiments set up in different seasons. In each experiment, faeces containing eggs of gastrointestinal nematodes were mixed with 11,000 chlamydospores/g and deposited on pasture plots. A comparison between fungal-added faeces and control faeces without fungus were made with regard to pasture infectivity, larval presence in faecal pats, faecal cultures, faecal pat weight, and temperature inside the faecal mas...

Experimental Parasitology

The nematophagous fungus Duddingtonia flagrans, used for the biological control of gastrointestin... more The nematophagous fungus Duddingtonia flagrans, used for the biological control of gastrointestinal nematodes in livestock, is fed to infected animals so its chlamydospores and the parasite eggs are voided together with faeces where the fungus preys on nematode larvae, thus reducing pasture infectivity. The number of chlamydospores needed for the fungus to be efficient in the presence of a wide range in numbers of parasitic eggs is largely unknown and a matter of discussion. The aim of this study was to determine the fungal efficacy of four different chlamydospore concentrations against three different levels of cattle faecal egg counts. Fungal concentrations of 11000, 6250, 3000 and 1000 chlamydospores/gram of faeces (cpg) were added to cultures containing 840, 480 or 100 eggs/gram of faeces (epg). After 14 days of incubation, the efficacy of D. flagrans, in decreasing order of chlamydospore concentrations, ranged from 100% (P < 0.0001) to 77% (P > 0.0999) in the 100 epg groups; 100% (P < 0.0001) to 92% (P = 0.4625) in the 480 epg groups and 100% (P < 0.0001) to 96% (P = 0.7081) in the 840 epg groups. The results indicate that the numbers of eggs in cattle faeces were not a determining factor on the fungal efficacy against gastrointestinal nematodes.

Parasitology Research

The aim of this experiment was to determine the yield of Haemonchus contortus third-stage larvae ... more The aim of this experiment was to determine the yield of Haemonchus contortus third-stage larvae (L3) in faecal cultures in different conditions, including incubation time (7 or 14 days), the addition of inert additives (polystyrene pellets, vermiculite or no additive) and physical condition of the incubated faeces (ground or whole pellets). Twelve groups of 10 cultures each were arranged and incubated at 24 °C to evaluate the interaction of the above-mentioned conditions. Significantly, more L3 (p=0.0019 to p=0.0200) were recovered from cultures incubated for 7 days than for 14 days, except for the groups containing whole pellets with no additives (p=0.53) or with vermiculite (p=0.41). Larval yields from 7-day incubated cultures did not differ between groups (p=0.47), but for the whole pellets with vermiculite group, which yielded significantly less L3 (p<0.0001) than the rest of the cultures. Incubation for 14 days showed that cultures containing whole pellets with no additives yielded significantly more L3 (p<0.05) than the rest. Culturing faeces with H. contortus seems not to require inert additives or extra manipulation to obtain good L3 yields.

Biocontrol Science and Technology

ABSTRACT The oral application of chlamydospores of the nematophagous fungus Duddingtonia flagrans... more ABSTRACT The oral application of chlamydospores of the nematophagous fungus Duddingtonia flagrans allows reducing the number of infective larvae (L3) in faeces and decreases the infectivity of the pastures of gastrointestinal nematodes. There are differences in the literature about the quantity of chlamydospores required for the reduction of L3 and there is little data about the importance of the concentration of parasite eggs in faeces in relation to the predatory effect of fungus. This study evaluated the reduction of L3 in faeces taking into account four concentrations of chlamydospores of D. flagrans with four concentrations of faecal eggs per gram (epg). Two hundred coprocultures were performed with 10 g each one, using faeces from four parasitised sheep with natural infections. The coprocultures were distributed in treated groups (GT) containing 180, 620, 1460 and 3600 epg along with 1000, 6250, 3000 and 11,000 chlamydospores per gram of faeces. Four control groups without chlamydospores were performed for each GT. The coprocultures were incubated for 16 days at room temperature of 27°C. The reduction percentages for the group of 11,000 chlamydospores and epg 180, 620, 1460 and 3600 were 6.51%; 1.35%; 52% and 85%, respectively. In the group of 6250 chlamydospores the reduction percentages for epg 180, 620, 1460 and 3600 were 16%; 20%; 66% and 67%, respectively. These results would indicate that the predatory capacity of D. flagrans can be dependent on the stimulus generated by the presence of larvae as well as the concentration of chlamydospores present in the faeces.

Veterinary Parasitology

The recovery of fenbendazole efficacy against Haemonchus contortus was attempted in a sheep inten... more The recovery of fenbendazole efficacy against Haemonchus contortus was attempted in a sheep intensive production system, using a strategy of population replacement in which the initial absolute efficacy of fenbendazole was 0%. The strategy was based on managing the parasite populations in refugia. Firstly, the resistant parasite population was reduced by means of anthelmintic treatments with efficacious drugs (Phase I), then a new, susceptible population was introduced in summer by way of artificially infected lambs at weaning, which were left to graze on the experimental pasture for eleven months (Phase II). Lastly, the impact of the replacement strategy, in terms of benzimidazole efficacy, was measured (Phase III). Faecal egg counts from permanent lambs and worm burdens as a measure of pasture infectivity from tracer lambs were determined throughout the study. During Phase I, faecal egg counts diminished from a peak of 2968 (300-7740) epg to 0 epg at the end, while adult worm burdens of H. contortus were reduced from 2625 (800-5100) to 0, which showed that the treatment strategy used in Phase I was effective in reducing the resistant population. These parameters also showed that good levels of pasture contamination and infectivity were achieved in Phase II, as faecal egg counts of up to 7275 (3240-13080) epg and adult worm burdens of 500 (200-800) H. contortus were reached. The absolute benzimidazole efficacy on H. contortus estimated at 16 months post-population replacement (Phase III) was 97.58%. The results lead to the conclusion that the recovery of anthelmintic efficacy of fenbendazole against a resistant population of H. contortus may be achieved by means of a strategy based on management of refugia and a subsequent introduction of a susceptible population. This strategy might be translatable to other resistant nematode genera.

Molecular and biochemical parasitology, Jan 25, 2018

The use of Triclabendazole for controlling fasciolosis is compromised by increased drug resistanc... more The use of Triclabendazole for controlling fasciolosis is compromised by increased drug resistance affecting livestock and humans. Although the mode of action of TCBZ is still unknown, putative candidates and markers of resistance have been advanced. A single nucleotide polymorphism (T687 G) in F. hepatica PGP was proposed as marker of resistance in a small scale study of European susceptible and resistant flukes, but the association was not found in Australian samples. The T687 G SNP was absent in more than 40 samples from 2 TCBZ-resistant and 3 susceptible isolates across Latin America here analyzed. While the American samples showed more variable SNPs than the previous ones, none of the SNPs detected showed a marked association with resistance. Analyzing the 42 kb of the FhPGP gene based on RNAseq data highlights that the variation has been underestimated, suggesting that more detailed efforts are needed in order to identify markers of resistance.

Veterinary Parasitology

The maintenance of anthelmintic-susceptible parasite refugia to delay the onset of anthelmintic r... more The maintenance of anthelmintic-susceptible parasite refugia to delay the onset of anthelmintic resistance is an almost impossible effort in many grazing livestock production countries given that current refugia consist of already resistant parasites. Rather, efforts could be focused on replacing the resistant parasite refugia by susceptible parasite ones and implementing sustainable parasite control measures from then on. To this purpose, a trial was conducted to attempt to establish a new population of ivermectin-susceptible Cooperia sp. on a beef cattle farm with proven problems of ivermectin-resistant Cooperia. During two consecutive years, 82 (Year 1) and 100 (Year 2) recently weaned and parasite-free heifers were inoculated with 40,000 or 30,000 susceptible Cooperia L3, respectively, at a time when levels of resistant parasite refugia were normally low. The animals were subsequently allowed to graze on the problem pastures during autumn until the end of spring. Levels of parasitism in the animals and on pasture were monitored monthly and animals were treated with levamisole when needed. The combination of parasitological monitoring and local epidemiological knowledge was essential to determine when treatments were to be administered. No clinical signs of gastrointestinal parasitosis in the herd were observed throughout the study and unnecessary treatments were avoided. Faecal egg counts reduction tests (FECRT) and controlled efficacy tests (CET) employing worm counts were carried out at different times throughout the study to determine the clinical efficacy (FECRT) and the absolute efficacy (CET) of ivermectin, respectively. The clinical efficacy of ivermectin increased from an initial 73% to 99.4%, while the absolute efficacy increased from 54.1% to 87.5% after just two animal production cycles. The switch from a resistant parasite population to a susceptible one requires knowledge of parasitological epidemiology, especially in relation to seasonal variations of parasite populations in both the host and in refugia.

Veterinary Parasitology: Regional Studies and Reports, 2017

This business plan seeks to demonstrate the feasibility and profitability of the creation and imp... more This business plan seeks to demonstrate the feasibility and profitability of the creation and implementation of a company dedicated to the production and marketing of 100% organic corn tortillas, in the city of Quito, over a 5-year financial period. The brand known as "Doña Benny" is located within the industry of other milling products with ISIC: C1071.09. The corn tortillas are designed for the north sectors of Quito, Cumbaya and Valle de los Chillos, which are interested in consuming corn tortillas at home, as well as better food and variety in their diet. For the production of corn tortillas, the Nixtamal process is implemented, achieving a better flavor and an increase in nutritional characteristics. During the entire production process, from the raw material to the delivery, the product will maintain its organic integrity, which is its main differentiator. In this way, this thesis seeks to generate a correct operation system for the company and also to reflect the value of the product, for which the clients are paying. Finally, the results show how with an initial investment of US $ 30,472.53, a positive NPV of US $ 1,800.73 and an IRR of 12.98 percentage points is obtained. This reflects the feasibility and profitability of the project.

Journal of Helminthology, 2015

The possible environmental effects of the massive use of Duddingtonia flagrans for controlling sh... more The possible environmental effects of the massive use of Duddingtonia flagrans for controlling sheep nematodes were evaluated in two regions. Non-supplemented faeces and faeces from sheep supplemented with D. flagrans were deposited three times on pasture plots and samples were collected 7 and 14 days post-deposition. Samples were cultured in agar-water (2%) with Panagrellus spp. to recover D. flagrans and other nematophagous fungi, and soil nematodes were extracted using Baermann funnels and counted. No significant differences in the populations of soil nematodes and fungi colonizing sheep faeces (P > 0.05) were observed between supplemented and non-supplemented groups, except in one sample. The topsoil in contact with the faeces was sampled 1–4 months post-deposition, revealing that, with one exception, D. flagrans did not persist in soil beyond 2 months post-deposition. Duddingtonia flagrans does not affect faecal colonization by other fungi and soil nematodes and, once deploy...

Veterinary parasitology, Jan 15, 2014

A study was conducted in sheep on Canadian farms to describe the relationship between packed cell... more A study was conducted in sheep on Canadian farms to describe the relationship between packed cell volume (PCV) or fecal egg counts (FEC) and subjective clinical parameters that may indicate the severity of parasitic gastroenteritis. Twenty-one farms in Ontario (ON) and 8 farms in Quebec (QC) were purposively selected and visited during April-May (spring) and August (summer) 2007. At each farm visit, blood and fecal samples were collected from 10 ewes and 10 female lambs; body condition score (BCS), dag score (DS), fecal consistency score (FCS) and FAMACHA score were recorded for all sampled sheep. Packed cell volume was determined for all blood samples, and FEC were performed for all fecal samples. Summary statistics and simple correlations were performed for the parameters recorded. Two mixed models with random effects at the farm level were developed; one using PCV as the response variable and another using the natural log of eggs per gram of feces (lnEPG). Finally, the residuals ...

Revista Iberoamericana de Micología, 2015

Biological control of gastrointestinal nematodes of ruminants by use of nematophagous fungi would... more Biological control of gastrointestinal nematodes of ruminants by use of nematophagous fungi would become part of any livestock parasite integral control system. Identifying autochthonous species that could then be selected for mass production is an important phase in the practical use of biological control. To search for nematophagous fungi with potential use as biological control agents against gastrointestinal nematodes in Argentina. Decomposing cattle faeces sampled in different locations were incubated in water agar 2% with Panagrellus sp. The developed nematophagous fungi were transferred to new water agar 2% plates and then to corn meal agar plates in order to carry out their identification. Fungal diversity and richness were also assessed. Seventeen species from nine genera of nematophagous fungi were found. Twelve species were nematode-trapping fungi and three species plus two fungi identified to genus level corresponded to endoparasitic fungi. Arthrobotrys conoides, Arthrobotrys oligospora, Duddingtonia flagrans, Monacrosporium doedycoides, Arthrobotrys robusta and Drechmeria coniospora were the most frequently isolated species overall in the whole study (6.6%, 5.7%, 5.7%, 5.7%, 4.7% and 4.7%, respectively) although other species were more frequently recorded at local levels such as Arthrobotrys pyriformis (18.8%). Only A. conoides has been previously isolated from ruminant faecal samples in Argentina. Five nematode-trapping fungal species are mentioned for the first time in the Americas CONCLUSIONS: D. flagrans and A. conoides, both identified in the present study, are among the most promising ones as biological control agents against gastrointestinal nematodes of ruminants.

Journal of Helminthology, 1999

Veterinary parasitology, Jan 30, 2018

Sheep production in tropical and temperate regions is hampered by the presence of Haemonchus cont... more Sheep production in tropical and temperate regions is hampered by the presence of Haemonchus contortus, the blood-sucking nematode that is the major cause of economic losses in small ruminant enterprises. The most limiting factor in the control of this parasitic disease is the steady progress of anthelmintic resistance worldwide. The search for control strategies that minimise the use of anthelmintics is therefore central to various efforts worldwide. One strategy is the introduction of susceptible parasites in refugia when these refugia are at low levels. This strategy could lead to a renewed possibility anthelmintics being effective. At farm level, this management practice could recover the use of anthelmintics in flocks with high levels of resistance. This review explores the possibility of replacing resistant H. contortus populations with susceptible ones through refugia management and. highlights the experiences of on-farm research attempts carried out in different geographical...

Veterinary Parasitology, 2019

The recovery of fenbendazole efficacy against Haemonchus contortus was attempted in a sheep inten... more The recovery of fenbendazole efficacy against Haemonchus contortus was attempted in a sheep intensive production system, using a strategy of population replacement in which the initial absolute efficacy of fenbendazole was 0%. The strategy was based on managing the parasite populations in refugia. Firstly, the resistant parasite
population was reduced by means of anthelmintic treatments with efficacious drugs (Phase I), then a new, susceptible population was introduced in summer by way of artificially infected lambs at weaning, which were left to graze on the experimental pasture for eleven months (Phase II). Lastly, the impact of the replacement strategy, in terms of benzimidazole efficacy, was measured (Phase III). Faecal egg counts from permanent lambs and worm burdens as a measure of pasture infectivity from tracer lambs were determined throughout the study.
During Phase I, faecal egg counts diminished from a peak of 2968 (300–7740) epg to 0 epg at the end, while adult worm burdens of H. contortus were reduced from 2625 (800–5100) to 0, which showed that the treatment strategy used in Phase I was effective in reducing the resistant population. These parameters also showed that good levels of pasture contamination and infectivity were achieved in Phase II, as faecal egg counts of up to 7275 (3240–13080) epg and adult worm burdens of 500 (200–800) H. contortus were reached. The absolute benzimidazole efficacy on H. contortus estimated at 16 months post-population replacement (Phase III) was 97.58%. The results lead to the conclusion that the recovery of anthelmintic efficacy of fenbendazole against a resistant population of H. contortus may be achieved by means of a strategy based on management of refugia and a subsequent introduction of a susceptible population. This strategy might be translatable to other resistant nematode genera.

Veterinary Parasitology, 2018

Pathogens

Experimental Parasitology

Parasitology Research

Biocontrol Science and Technology

Veterinary Parasitology

Molecular and biochemical parasitology, Jan 25, 2018

Veterinary Parasitology

Veterinary Parasitology: Regional Studies and Reports, 2017

Journal of Helminthology, 2015

Veterinary parasitology, Jan 15, 2014

Revista Iberoamericana de Micología, 2015

Journal of Helminthology, 1999

Veterinary parasitology, Jan 30, 2018

Veterinary Parasitology, 2019

The recovery of fenbendazole efficacy against Haemonchus contortus was attempted in a sheep inten... more The recovery of fenbendazole efficacy against Haemonchus contortus was attempted in a sheep intensive production system, using a strategy of population replacement in which the initial absolute efficacy of fenbendazole was 0%. The strategy was based on managing the parasite populations in refugia. Firstly, the resistant parasite
population was reduced by means of anthelmintic treatments with efficacious drugs (Phase I), then a new, susceptible population was introduced in summer by way of artificially infected lambs at weaning, which were left to graze on the experimental pasture for eleven months (Phase II). Lastly, the impact of the replacement strategy, in terms of benzimidazole efficacy, was measured (Phase III). Faecal egg counts from permanent lambs and worm burdens as a measure of pasture infectivity from tracer lambs were determined throughout the study.
During Phase I, faecal egg counts diminished from a peak of 2968 (300–7740) epg to 0 epg at the end, while adult worm burdens of H. contortus were reduced from 2625 (800–5100) to 0, which showed that the treatment strategy used in Phase I was effective in reducing the resistant population. These parameters also showed that good levels of pasture contamination and infectivity were achieved in Phase II, as faecal egg counts of up to 7275 (3240–13080) epg and adult worm burdens of 500 (200–800) H. contortus were reached. The absolute benzimidazole efficacy on H. contortus estimated at 16 months post-population replacement (Phase III) was 97.58%. The results lead to the conclusion that the recovery of anthelmintic efficacy of fenbendazole against a resistant population of H. contortus may be achieved by means of a strategy based on management of refugia and a subsequent introduction of a susceptible population. This strategy might be translatable to other resistant nematode genera.

Veterinary Parasitology, 2018

Veterinary Parasitology: Regional Studies and Reports, 2017

A B S T R A C T The presence of anthelmintic resistance in Argentina has experienced a marked inc... more A B S T R A C T The presence of anthelmintic resistance in Argentina has experienced a marked increase in cattle, with numerous reports showing levels of resistance of different parasite genera to different chemical groups. The aim of this study is to update comprehensively the situation of anthelmintic resistance to the different chemical groups in the most important areas of cattle production in Argentina. The study involved the determination of anthelmintic resistance in 62 cattle farms in 7 provinces using the faecal egg count reductions test. The results showed a marked increase of anthelmintic resistance compared to previous reports; the main resistant genera were Cooperia and Haemonchus to ivermectin, Ostertagia and Cooperia to ricobendazole, and Haemonchus to fenbendazole. There was also a distinct difference in clinical efficacies between subcutaneous ricobendazole and oral fenbendazole in favour of the latter, probably attributed to the administration route. Levamisole has showed high efficacy and broad antiparasitic spectrum. Anthelmintic resistance is widely and firmly established in grazing cattle production systems in the country; the diagnosis of resistance must be done in every particular farm in order to design a sustainable parasite control based on anthelmintics use.

A B S T R A C T The maintenance of anthelmintic-susceptible parasite refugia to delay the onset o... more A B S T R A C T The maintenance of anthelmintic-susceptible parasite refugia to delay the onset of anthelmintic resistance is an almost impossible effort in many grazing livestock production countries given that current refugia consist of already resistant parasites. Rather, efforts could be focused on replacing the resistant parasite refugia by susceptible parasite ones and implementing sustainable parasite control measures from then on. To this purpose, a trial was conducted to attempt to establish a new population of ivermectin-susceptible Cooperia sp. on a beef cattle farm with proven problems of ivermectin-resistant Cooperia. During two consecutive years, 82 (Year 1) and 100 (Year 2) recently weaned and parasite-free heifers were inoculated with 40,000 or 30,000 susceptible Cooperia L3, respectively, at a time when levels of resistant parasite refugia were normally low. The animals were subsequently allowed to graze on the problem pastures during autumn until the end of spring. Levels of para-sitism in the animals and on pasture were monitored monthly and animals were treated with levamisole when needed. The combination of parasitological monitoring and local epidemiological knowledge was essential to determine when treatments were to be administered. No clinical signs of gastrointestinal parasitosis in the herd were observed throughout the study and unnecessary treatments were avoided. Faecal egg counts reduction tests (FECRT) and controlled efficacy tests (CET) employing worm counts were carried out at different times throughout the study to determine the clinical efficacy (FECRT) and the absolute efficacy (CET) of ivermectin, respectively. The clinical efficacy of ivermectin increased from an initial 73% to 99.4%, while the absolute efficacy increased from 54.1% to 87.5% after just two animal production cycles. The switch from a resistant parasite population to a susceptible one requires knowledge of parasitological epidemiology, especially in relation to seasonal variations of parasite populations in both the host and in refugia.

The possible environmental effects of the massive use of Duddingtonia flagrans for controlling sh... more The possible environmental effects of the massive use of Duddingtonia flagrans for controlling sheep nematodes were evaluated in two regions. Non-supplemented faeces and faeces from sheep supplemented with D. flagrans were deposited three times on pasture plots and samples were collected 7 and 14 days post-deposition. Samples were cultured in agar-water (2%) with Panagrellus spp. to recover D. flagrans and other nematophagous fungi, and soil nematodes were extracted using Baermann funnels and counted. No significant differences in the populations of soil nematodes and fungi colonizing sheep faeces (P. 0.05) were observed between supplemented and non-supplemented groups, except in one sample. The topsoil in contact with the faeces was sampled 1 –4 months post-deposition, revealing that, with one exception, D. flagrans did not persist in soil beyond 2 months post-deposition. Duddingtonia flagrans does not affect faecal colonization by other fungi and soil nematodes and, once deployed on pasture, does not survive for long periods in the environment.

Desarrollo de una forma de administración de Duddingtonia flagrans mediante bioencapsulación para... more Desarrollo de una forma de administración de Duddingtonia flagrans mediante bioencapsulación para su potencial uso en control biológico de parásitos gastrointestinales de rumiantes

El control biológico mediante el uso de hongos nematófagos es una herramienta para el control de ... more El control biológico mediante el uso de hongos nematófagos es una herramienta para el control de los nematodos gastrointestinales (NGI) de bovinos. Mientras que los antihelmínticos (ATH) actúan principalmente sobre los estadíos parasitarios dentro del animal, los hongos actúan en la materia fecal, afectando a las larvas de NGI desarrolladas a partir de los huevos eliminados con la misma. El objetivo del presente trabajo fue determinar in vitro el efecto de los 5 ATH más usados en la producción bovina argentina sobre el hongo nematófago Duddingtonia flagrans en placas de agar maíz (CMA) y en coprocultivos. El efecto de los ATH sobre el crecimiento del hongo se determinó en placas de Petri con CMA 2% incubadas por separado en presencia de IVM, 2 ppm; LVM, ABZ, FBZ y RBZ, 1 ppm, a las cuales se les agregó 1 cm2 de CMA con D. flagrans. Las placas se incubaron a 27ºC durante 9 días. Diariamente, se midió el crecimiento micelial radial. El efecto de cada ATH sobre la capacidad predadora de D. flagrans se determinópor medio de coprocultivos con huevos de NGI, ATH y el hongo, incubados durante 14 días a temperatura ambiente. Luego se recuperaron, contaron e identificaron las larvas 3 (L3) desarrolladas. Ambos ensayos contaron con los correspondientes controles para el hongo, los ATH y el diluyente (metanol). En cuanto al crecimiento del hongo, las placas con metanol, RBZ y LVM mostraron un crecimiento promedio similar al grupo control (5 mm/día). Las placas con IVM mostraron un ritmo de crecimiento menor al control, especialmente entre los días 3 y 6 de medición (P<0.05 – P<0.01), sin embargo el micelio se expandió hasta el borde de la placa al día 9. El crecimiento en las placas con ABZ y FBZ fue de 0.6 y 0.3 mm/día, respectivamente, resultando ambos significativamente menores (P< 0.001) que el control. Con respecto a la capacidad predadora del hongo sobre los NGI, D. flagrans presentó una eficacia de 91.8, 90.1 y 89.1% en los grupos control, LVM y metanol, respectivamente; mientras que el número de L3 en los grupos ABZ, FBZ, RBZ e IVM fue escaso o nulo, tanto en los grupos con el hongo como sus controles. Estos resultados preliminares muestran que el metanol y LVM no afectarían el crecimiento ni la capacidad predadora de D. flagrans, mientras que la acción de ABZ, FBZ, RBZ e IVM sobre la fase de vida libre de los NGI en los coprocultivos habría interferido sobre la capacidad del hongo de predar eficazmente.
Financiamiento: CONICET (PIP #112-201301-00546)

Methodology Glycerol and dialdehyde starch were used as plasticizer and cross-linking agent, resp... more Methodology Glycerol and dialdehyde starch were used as plasticizer and cross-linking agent, respectively. Films were obtained by casting and molded by compression. The films of group A (GA) and group B (GB) were obtained by casting. In GA 696.300 chlamydospores were placed on the material surface, in the GB the same number of chlamydospores was sprinkled on an adhesive liquid made of soy protein. A third group (GC) comprised of films molded by compression with chlamydospores incorporated the same way as GB. Three rolled up films from each group were immersed in distilled water at 27º C and constant agitation. Samples were taken every two hours during the first eight hours and then every 24 hours and the number of chlamydospores in each aliquot was determined until h 264 when the test ended.

Biological control by nematophagous fungi against gastrointestinal parasitic disease of ruminants... more Biological control by nematophagous fungi against gastrointestinal parasitic disease of ruminants is a ecologic method to reduce the use of anthelmintic synthetics in farm animal production. In this study, films made from soy protein (SP) were evaluated to ascertain the biodegradability and release of chlamydospores (CL) of Duddingtonia flagrans. The films of group A (GA) and group B (GB) were obtained by casting. In GA 696.300 CL were placed on the material surface, in the GB the same number of CL was sprinkled on an adhesive liquid made of SP. Third group (GC) comprised of films molded by compression with CL incorporated the same way as GB. Three rolled up films from each group were immersed in distilled water at 27º C and constant agitation. Samples were taken every two hours during the first eight hours and then every 24 hours and the number of CL in each aliquot was determined until h 264 when ended the test. The degradation began 48 h postinitiation of the experiment; GC disintegrated by h 144, while GA and GB degraded more slowly and maintained their rolled form until the end of the test. The release of CL depended on processing method and way of incorporating CL; GA started releasing CL by h 144 (6%) and reached 35% by h 264; GB started releasing CL by h 96 (15%) reaching 43% after 264 h. For GC the release was very fast, 96 h, which was associated with premature degradation of the support matrix. This preliminary study showed SPI films GA, as controlledrelease device and sustained CL D. flagrans and its potential application to the biological control by nematophagous fungi.

A recuperação da eficácia do fenbendazole em Haemonchus contortus através da gestão do refúgio e ... more A recuperação da eficácia do fenbendazole em Haemonchus contortus através da gestão do refúgio e substituição da população de parasitas Objective: To recover the high efficacy of fenbendazole (FBZ) on Haemonchus contortus resistant populations by means of worm refugia management and the introduction of artificially infected lambs with benzimidazole-susceptible nematodes. Methodology: The study was carried out in an experimental farm located in the southeast of Buenos Aires province, Argentina, where clinical efficacy of FBZ on total parasite population and absolute efficacy of FBZ on H. contortus were 82.2% and 0%, respectively. In Year 1, 40 Corriedale and Texel lambs and a pasture naturally infected with BDZ-resistant H. contortus were used. An anthelmintic treatment programme based on biweekly faecal egg counts was carried out with the sole purpose of diminishing the larval population on pasture (figure 1). In Year 2, 42 new weaned lambs were orally inoculated with 3000 infective larvae of H. contortus fully susceptible to BDZ and placed onto the pasture used the previous year, which allowed the BDZ-susceptible strain to be established as refugia. An accompanying nematode control programme carried out using faecal eggs counts and FAMACHA scores determined whether any individual treatment was needed, in which case the selected animals were treated with levamisole and taken out of the calculations. A faecal egg count reduction test (FECRT) and a controlled efficacy test (CET) were performed 16 months after inoculating the lambs with the susceptible strain in order to evaluate both, the clinical and absolute efficacy of FBZ. Results and Conclusions: The establishment of a FBZ-susceptible population of H. contortus can be appreciated through faecal egg counts from inoculated lambs in Figure 2. After a 16 month-period from the introduction of the susceptible H. contortus strain, the FECRT showed a clinical efficacy of 50.6% for the whole nematode population, while the CET showed an absolute efficacy for H. contortus of 97.8% after treating the lambs orally with FBZ (7.5 mg/kbw). The intestinal worms Nematodirus spathiger and Trichostrongylus colubriformis remained resistant to FBZ at the end of the study (table 1). The present work shows that it might be possible to mitigate the phenomenon of anthelmintic resistance through refugia management and the replacement of resistant worm population by susceptible ones.