ANIMAL MODELS FOR THE STUDY OF LEISHMANIASIS IMMUNOLOGY

Leishmaniasis remains a major public health problem worldwide and is classified as Category I by the TDR/WHO, mainly due to the absence of control. Many experimental models like rodents, dogs and monkeys have been developed, each with specific features, in order to characterize the immune response to Leishmania species, but none reproduces the pathology observed in human disease. Conflicting data may arise in part because different parasite strains or species are being examined, different tissue targets (mice footpad, ear, or base of tail) are being infected, and different numbers (“low” 1×102 and “high” 1×106) of metacyclic promastigotes have been inoculated. Recently, new approaches have been proposed to provide more meaningful data regarding the host response and pathogenesis that parallels human disease. The use of sand fly saliva and low numbers of parasites in experimental infections has led to mimic natural transmission and find new molecules and immune mechanisms which should be considered when designing vaccines and control strategies. Moreover, the use of wild rodents as experimental models has been proposed as a good alternative for studying the host-pathogen relationships and for testing candidate vaccines. To date, using natural reservoirs to study Leishmania infection has been challenging because immunologic reagents for use in wild rodents are lacking. This review discusses the principal immunological findings against Leishmania infection in different animal models highlighting the importance of using experimental conditions similar to natural transmission and reservoir species as experimental models to study the immunopathology of the disease

Frecuencia de alimentación e iluminación nocturna y productividad de vaquillas para engorda en verano

The combined effect of increasing feeding frequency and night lighting on feedlot performan- ce and carcass traits during summer was studied in 171 beef heifers. Treatments were: two rations daily (control group) and three rations daily (treated group), during a feedlot period of 84 days. Heifers received the same diets. Treated heifers were 16 kg heavier (p<0.05), had higher daily gain (0.140 kg d -1 ; p<0.05), and better feed conversion (7.69 vs. 8.69 dg d -1 ; p<0.05) than control heifers, although feed intake was similar. Control heifers showed higher (p<0.05) respiration rate than treated (93.5 vs. 83.9 breaths min -1 ), which suggests higher level of heat stress in those animals. Hot carcass weight was higher (p<0.05) in treated heifers than in control (244.3 vs. 233.9 kg); however, there were no differences in the other carcass traits. These results suggest that increasing feeding frequency and photoperiod during summer may improve feedlot performance and adaptation to high temperatures in beef heifers.Se determinó el efecto combinado de aumen- tar la frecuencia de alimentación e iluminación nocturna durante el verano en la respuesta pro- ductiva y características de la canal de 171 vaquillas de razas de carne. Los tratamientos fueron: dos raciones diarias (testigo) y tres raciones diarias más la iluminación del comedero de 12:00 a 02:00 h (tratado), durante 84 días. Las vaquillas recibie- ron las mismas dietas. Las vaquillas tratadas pesaron 16 kg más (p<0,05), tuvieron mayor ganancia diaria (0,140 kg d -1 ; p<0,05), y menor conversión alimenticia (7,69 vs. 8,69 kg; p<0,10) que el grupo testigo, pero el consumo de alimento no fue diferente. Las vaquillas testigo mostraron mayor (p<0,05) frecuencia respiratoria que las tratadas (93,5 vs. 83,9 resp min -1 ), lo que sugiere un mayor grado de estrés calórico en esos anima- les. El peso de la canal caliente fue mayor (p<0,05) en las vaquillas tratadas que en las testigo (244,3 vs. 233,9 kg), pero no hubo diferencias en otras características de la canal. Los resultados sugie- ren que el aumentar la frecuencia de alimentación y el fotoperiodo en verano pueden mejorar las respuestas productivas y la adaptación a tempe- raturas altas en vaquillas engordadas en corral

Viscosidad de la dieta y su efecto sobre la pérdida de aminoácidos endógenos recuperados en íleon terminal de cerdos

La viscosidad de la dieta provocada por algunos compuestos antinutricionales en los cereales puede afectar la pérdida de aminoácidos (AA) endógenos. Por tanto, se realizó un estudio para evaluar el efecto de la viscosidad de la dieta, producida por la adición de goma Guar, en la pérdida de AA endógenos recuperados al final del intestino delgado. Seis cerdos (62.0±2.5 kg peso) con cánulas en íleon terminal se utilizaron en tres periodos experimentales en un diseño en Cuadro Latino 3×3 repetido. Los tratamientos fueron: T1) dieta base semi-purificada con almidón de maíz, celulosa cristalina, sacarosa y aceite de soya; T2) dieta base más 0.5% de goma Guar; T3) dieta base más 1.0% de goma Guar. Una mezcla de vitaminas y minerales se adicionó a cada dieta para cubrir los requerimientos para cerdos en finalización. Además, se adicionó 0.2% de óxido crómico como marcador del flujo del contenido intestinal. La composición de AA de la proteína endógena, excepto por glicina, no se afectó (p>0.05) por la viscosidad de la dieta; el contenido de glicina fue superior (p=0.05) en los cerdos que recibieron la dieta con 1.0% de goma, comparado con los de la dieta base. La pérdida de la mayoría de los AA esenciales endógenos se redujo (p=0.03) por la adición de goma a la dieta, excepto para arginina (p>0.86) y valina (p>0.46). Independientemente del contenido de goma Guar en la dieta, la pérdida de AA no esenciales fue dos a tres veces superior a la de los esenciales. Los resultados indican que la mayor viscosidad del alimento, causada por la adición de goma Guar a dietas, disminuye la secreción endógena de la mayoría de AA esenciales y algunos no esenciales en cerdos

Interferon-gamma is required for the late but not early control of Leishmania amazonensis infection in C57Bl/6 mice

The critical role of interferon-gamma (IFN-g) in the resistance of C57Bl/6 mice to Leishmania major is widely established but its role in the relative resistance of these animals to L. amazonensis infection is still not clear. In this work we use C57Bl/6 mice congenitally deficient in the IFN-g gene (IFN-g KO) to address this issue. We found that IFN-g KO mice were as resistant as their wild-type (WT) counterparts at least during the first two months of infection. Afterwards, whereas WT mice maintained lesion growth under control, IFN-g KO mice developed devastating lesions. At day 97 of infection, their lesions were 9-fold larger than WT controls, concomitant with an increased parasite burden. At this stage, lesion-draining cells from IFN-g KO mice had impaired capacity to produce interleukin-12 (IL-12) and tumour necrosis factor-a in response to parasite antigens whereas IL-4 was slightly increased in comparison to infected WT mice. Together, these results show that IFN-g is not critical for the initial control of L. amazonensis infection in C57Bl/6 mice, but is essencial for the developmente of a protective Th1 type immune response in the later stages

Limnological Control of Brine Shrimp Population Dynamics and Cyst Production in the Great Salt Lake, Utah

In the Great Salt Lake of Utah, the brine shrimp Artemia franciscanaKellogg is an important food resource for birds and they produce dormant cysts that are harvested and used extensively in the aquaculture industry.We analyzed the limnological factors controlling Artemia growth and cyst production over 12 months in 1994 and 1995. Laboratory experiments showed that inter-brood intervals were highly dependent on temperature and slightly on food level. At optimal temperatures and nutritious food, juveniles reached reproductive size within 7 d in the laboratory. In winter when temperatures were less than 3 ◦C, Artemia were absent from the lake, phytoplankton abundance was high (≥13 Chl a μg l−1), and the dominant grazers were ciliated protozoans. In the spring, cysts hatched when phytoplankton was abundant (15–30 μg Chl a l−1), and the Artemia grew and produced large clutches of ovoviviparous eggs. Estimated naupliar production from these eggs was 80 l−1 from April to May. Despite the high production of nauplii, Artemia densities declined to 8 l−1by June and the growing shrimp population grazed down the phytoplankton resource to \u3c1 μg Chl a l−1. With the depleted phytoplankton food resource during the summer, Artemia growth slowed, lipid indices decreased, clutch sizes declined, and females switched primarily to oviparous cyst production. During the summer, there was limited production of ovoviviparous eggs, and limited recruitment of juveniles, probably due to low food. Although oviparous reproduction began in June, more than 90% of the cysts were produced after July when female densities had declined to 1.5 l−1, but nearly all of them were producing cysts. Estimated cyst production was 650 000 m−2, or 4.54 × 10^6 kg dry weight for the entire lake. The reported commercial harvest took 21% of the 1994 cyst production. That harvest had little impact on the subsequent year’s population, as Artemia densities were ultimately controlled by algal production in the lake