Resistencia antihelmíntica en equinos: Observaciones sobre el período de reaparición de huevos luego del tratamiento con ivermectina en potrancas y yeguas madres

En los equinos parasitados por los pequeños estróngilos, un menor período requerido luego del tratamiento con antihelmínticos para la reaparición de huevos (PRH) de los nematodes en la materia fecal, puede ser utilizado como un indicador de la presencia de resistencia o pérdida de eficacia a estas drogas. En el presente trabajo se evaluó la eficacia clínica y el PRH luego de tratamientos con ivermectina (0,2 mgr/kg) en equinos adultos (yeguas madres) y jóvenes (potrancas) naturalmente parasitados por pequeños estróngilos en un establecimiento de la provincia de Tucumán. La eficacia clínica determinada en la segunda semana post-tratamiento y utilizando un test de reducción en el conteo de huevos, osciló entre el 99,8 y el 100% en yeguas y potrancas respectivamente. Por su parte el PRH (considerado como el período post- tratamiento en que se alcanza el 10% del hpg pre-tratamiento o una reducción del mismo < 90%) fue de seis y siete semanas para las potrancas y yeguas madres respectivamente (p=0,001). En la sexta semana post- tratamiento, las potrancas mostraron poseer 11,74 veces más riesgo (IC 95% = 2,58-53,38) de reaparición de huevos que las yeguas madres. Estas diferencias ocasionadas por la edad de los animales deberían considerarse cuando se realizan estudios para establecer el status de susceptibilidad o resistencia a los antihelmínticos basados en el PRH para evitar asunciones incorrectas sobre el mismo.

In horses parasitized by small strongyles, a shortened strongyle egg reappearance period (ERP) after treatment with anthelmintics is considered an early indicator of the presence of resistance or loss of efficacy to these drugs. In the present work, clinical efficacy and ERP were evaluated after treatments with ivermectin in adult horses (broodmares) and juveniles (its fillies) naturally parasitized by small strongyles in an farm of Tucumán province. The clinical efficacy determined in the second week after treatment, and using a test of reduction in the egg count, ranged between 99.8 and 100% in mares and fillies respectively. The ERP (considered as the post- treatment period in which 10% of the pre-treatment epg was reached or a reduction of it < 90%) was six and seven weeks for the fillies and mother mares respectively (p= 0.001). In the sixth week after treatment, the fillies showed 11.74 times more risk (95% CI = 2.58-53.38) of reappearance of eggs than the brood mares. These differences caused by the age of the animals should be considered when conducting studies to establish the status of susceptibility or resistance to anthelmintics based on the ERP to avoid incorrect assumptions.

Influence of hard water on the bioavailability of enrofloxacin in broilers.

To define the impact that use of different levels of hard water has on the bioavailability of the antibacterial, enrofloxacin, in poultry, an oral bioavailability-pharmacokinetic study of the drug was carried out. Two hundred fifty clinically healthy broilers, divided into 5 groups, were individually dosed orally with 10 mg/kg of enrofloxacin diluted to 0.1%. The enrofloxacin was diluted with water of increasing hardness in accordance with an international grading system. After dosing, blood samples were obtained at predetermined times. Serum was recovered and quantified for enrofloxacin by means of an agar diffusion bacteriological method. The composite serum concentrations of enrofloxacin and metabolites vs. time relationships were analyzed using software for compartmental pharmacokinetics. Results show that there were statistically significant differences in the following pharmacokinetic variables: maximal serum concentrations (Csmax), area under the time vs. concentration curves, and half-lives of the elimination phases. The means of these values showed a linear decay of Csmax from one group to the next as water hardness increased. Chemical analysis of water calcium and magnesium ions revealed the formation of coordination groups. Lack of interference with the microbiological activity in vitro of enrofloxacin diluted in hard water indicated that diminished absorption may be partly responsible for reduction in bioavailability. These results stress the need for proper water supply when enrofloxacin is used and point out a factor that must be taken into account when clinical outcomes do not comply with expectations.

Asphalt volcanism and chemosynthetic life in the Campeche Knolls, Gulf of Mexico.

In the Campeche Knolls, in the southern Gulf of Mexico, lava-like flows of solidified asphalt cover more than 1 square kilometer of the rim of a dissected salt dome at a depth of 3000 meters below sea level. Chemosynthetic tubeworms and bivalves colonize the sea floor near the asphalt, which chilled and contracted after discharge. The site also includes oil seeps, gas hydrate deposits, locally anoxic sediments, and slabs of authigenic carbonate. Asphalt volcanism creates a habitat for chemosynthetic life that may be widespread at great depth in the Gulf of Mexico.

Correlation between gestational age, weight, or ponderosity and serum thyroxine concentration at birth.

Thyroxine levels were measured in cord blood sera from 2,1800 healthy infants born of "low-risk" mothers in Los Angeles. Variations of T4 with gestational age, birth weight, ponderosity (size related to weight), sex, and race were studied, as well as the variation of W and P with GA. Over the range of GA 30 to 47 weeks, serum T4 concentrations, W, and P each increase with GA, leveling off to approximately constant values from 42 to 47 weeks; the increases are 12, 66, and 20%, respectively. For a fixed GA, T4 increases with increasing W but is not correlated with P; W, GA, and their product are useful measurements for predicting T4, but P is not. Formulas for predicting cord T4 are given for possible use in improving computer-assisted screening programs for congenital hypothyroidism; mean T4 values (+/- I SD) are tabulated against W and GA.

Thyroid function at birth in infants of 30 to 45 weeks' gestation.

Serum T4 was measured in cord blood of 2,683 infants of gestational ages 30 to 45 weeks and birth weights of 1,460 to 5,250 gm. In addition, serum TBG was measured in 180, and serum TSH in 125 of these infants. Mean serum T4 increased with gestational age from 9.4 microng/dl at 30 weeks to 11.7 at 45 weeks. TBG varied from 3.1 to 11.4 mg/dl but showed no correlation with gestational age. There was a positive correlation between T4 and TBG. Serum TSH levels showed a significant negative correlation with gestational age, decreasing from 15 micronU/ml at 30 weeks to 7 micronU/ml at 45 weeks, while the serum T4/TSH ratio increased from 0.6 to 1.6. The results indicate that cord, T4 varies mainly with TBG, and to a lesser extent with gestational age.