Gastrointestinal nematodes (GIN) of ruminants (cattle, sheep and goats) are ubiquitous and can cause severe injuries to infected animals and significant losses in farming revenues. GIN are able to survive severe environmental and host conditions, but mankind has developed a number of ingenious methods for parasite control. The commerce and use of modern anthelmintic drugs with a broad spectrum of activity has been a solid tool for nearly 40 years, however the continuous use of these drugs, has led to the selection of populations of drug-resistant worms worldwide. At present, the ever-growing agricultural systems in Latin America are facing many challenges and cannot rely on the far-reaching objective of parasitic elimination from the host or the environment. The lack of extensive programs for monitoring drug resistance exacerbates the negative consequences of reduced efficacy, which is evident in some areas with the increase in mortality rate even after treatment. Experts agree that new schemes of parasitic control are needed and should be based on the strategy of targeted selective treatment where affected hosts are identified and treated accordingly. In this article, we will focus our discussion on the challenges for the control of GIN in Latin America by 2020 imposed by reduced drug efficacy. We will evaluate phenotypic and molecular markers, methods for single-animal evaluation, and the implementation of schemes for anthelmintic treatment that address parasites in refugia.

The present study is part of an ongoing investigation into the characteristics of Myxozoan parasites of Brazilian freshwater fish and was carried out using morphology, histopathology and electron microscopy analysis. A new Myxosporea species (Henneguya pseudoplatystoma) is described causing an important reduction in gill function in the farmed pintado (a hybrid fish from a cross between Pseudoplatystoma corruscans and Pseudoplatystoma fasciatum), which is a commercially important South American catfish. From a total of 98 pintado juveniles from fish farms in the states of São Paulo and Mato Grosso do Sul (Brazil), 36 samples (36.7%) exhibited infection of the gill filaments. Infection was intense, with several plasmodia occurring on a same gill filament. The plasmodia were white and measured up to 0.5mm in length; mature spores were ellipsoidal in the frontal view, measuring 33.2+/-1.9 microm in total length, 10.4+/-0.6 microm in body length, 3.4+/-0.4 microm in width and 22.7+/-1.7 microm in the caudal process. The polar capsules were elongated, measuring 3.3+/-0.4 microm in length and 1.0+/-0.1 microm in width and the polar filaments had six to seven turns. Histopathological analysis revealed the parasite in the connective tissue of the gill filaments and lamella. No inflammatory process was observed, but the development of the plasmodia reduced the area of functional epithelium. Ultrastructural analyses revealed a single plasmodial wall, which was in direct contact with the host cells and had numerous projections in direction of the host cells as well as extensive pinocytotic canals. A thick layer (2-6 microm) of fibrous material and numerous mitochondria were found in the ectoplasm. Generative cells and the earliest stage of sporogenesis were seen more internally. Advanced spore developmental stages and mature spores were found in the central portion of the plasmodia.

Leishmaniasis is a "neglected tropical disease" and serious public health issue in Brazil. While dogs are recognized as particularly important reservoirs, recent reports of domestic cats infected with Leishmania sp. in urban areas suggest their participation in the epidemiological chain of the parasite in endemic areas. The aim of this study was to screen domestic cats for Leishmania sp. infection in an area where human and canine visceral leishmaniasis are endemic, followed by the identification of the species circulating in cats. We collected peripheral blood, lymph-node aspirates and bone marrow from 100 adult animals, both male and female, and analyzed the samples using cytological and molecular (PCR) detection techniques. We detected Leishmania in 6% of animals, which were then analyzed by RFLP-PCR to identify the species. Leishmania infantum (synonym: L. chagasi), a species responsible for visceral leishmaniasis in humans and other animals, was identified from all six samples. Amastigotes were observed in the peripheral blood, bone marrow and lymph-node aspirates in 4 of the 6 PCR-positive animals. The presence of infected cats in endemic areas should not be neglected, because it demonstrates the potential role of these animals in the biological cycle of the pathogen.

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The performance of grazing cattle in tropical areas is deeply influenced by parasitism, and the increasing reports of resistance are a threat to effective nematode control. The present study aimed to evaluate the effect of avermectins on the performance of weaned calves naturally infected by ivermectin-resistant gastrointestinal nematodes. The effect of four commercial endectocides (ivermectin 2.25 % + abamectin 1.25 %, ivermectin 3.15 %, doramectin 3.15 %, and doramectin 1 %) on parasitism and performance of a hundred weaned Nellore calves were evaluated during 112 days. The most effective anthelmintic showed efficacy of 84 % and resulted in an increase (P < 0.05) of live weight gain of 11.85 kg, compared to untreated group, 9.05 and 9.41 kg compared to those treated with more ineffective avermectins which showed efficacy of 0 and 48.2 %, respectively. A significant (P < 0.05) and weak negative correlation (r = -0.22) between the eggs per gram (EPG) and body weight was observed, indicating that even the low mean EPG (175 ± 150) observed at day 0 in the control group, with predominance of Haemonchus sp., was responsible for production losses. These results indicate that control of nematode parasites in beef cattle in the weaning phase may not result in increased productivity when carried out without technical criteria.