Pollen beetle (Astylus atromaculatus)-associated gastroenteric disease in cattle: report of 6 natural outbreaks.

Astylus atromaculatus is a pollen beetle native to South America, commonly found in crop flowers. Experimental intoxication of sheep and guinea pigs by this beetle resulting in fibrinonecrotizing enteritis has been reported. We describe here 6 natural outbreaks of intoxication in cattle associated with consumption of alfalfa (5 of 6) and mixed native (1 of 6) pastures heavily contaminated with A. atromaculatus. The outbreaks occurred during the summer (January-February) of 2023 in Argentina (n = 4) and Uruguay (n = 2), in beef cattle under extensive or semi-extensive rearing systems, with overall cumulative incidence and mortality of 22.3% and 17.8%, respectively. The main clinical signs included acute onset of anorexia, lethargy, hyperthermia, hindlimb weakness, reluctance to move, and diarrhea, for up to 15 d. In 2 outbreaks, sudden death was observed. Eight Hereford, Angus, and/or crossbreed heifers, cows, steers, and/or calves were autopsied. Gross and microscopic findings included multifocal necrosis with fibrinous pseudomembranes in the forestomachs and/or small and large intestines. Fragments or whole specimens of A. atromaculatus were identified in the ruminal content of all animals. Testing for multiple gastroenteric pathogens was negative as was testing of A. atromaculatus for cantharidin and batrachotoxin. GC-MS and LC-MS/MS performed on the beetles did not identify any known toxic compounds. Based on the exposure to A. atromaculatus-contaminated pasture, gross and microscopic lesions, and negative results of all testing for multiple gastroenteric pathogens, a diagnosis of intoxication by A. atromaculatus is proposed. Disease caused by A. atromaculatus consumption has not been reported previously in cattle, to our knowledge.

Hypomagnesemia in beef cattle / Hipomagnesemia em bovinos de corte

Hypomagnesemia is a major cause of death in grazing beef cows in countries of the Southern Hemisphere such as Argentina, Australia and New Zealand. Here we review the literature on hypomagnesemia in beef cattle and describe an outbreak in Uruguay. The disease occurred in late autumn, affecting 6 to 11-year-old Aberdeen Angus and Hereford x Aberdeen Angus lactating multiparous cows in good body condition, grazing on natural grasslands that had been improved by fertilization and sowing of seeds of ryegrass and oat. Approximately 40 out of 225 cows were affected and 24 (10.7%) died. A presumptive diagnosis of hypomagnesemia was established based on sudden death, acute neuromuscular clinical signs, epidemiological data, and the response to Mg administration. The diagnosis was confirmed by detecting low Mg concentrations in serum (0.47-0.57mmol/L), vitreous humor (0.47-0.80mmol/L), aqueous humor (0.66mmol/L) and cerebrospinal fluid (0.59mmol/L). The largest component of the diet corresponding to fast-growing and exuberant forages of ryegrass and oat had high concentrations of K (3.48%), N (4.38%) and P (0.94%), suggesting secondary hypomagnesemia. In addition, the K/(Ca+Mg) ratio was 2.38 in forages of ryegrass and oat (reference value: 2.2), and 0.15 in the soil (reference value: 0.09), which represent risk factors for hypomagnesemia. In conclusion, hypomagnesemia is an important cause of mortality in beef cattle grazing improved natural grasslands in Uruguay and it can be easily prevented by correct seasonal Mg supplementation.(AU)

A hipomagnesemia é uma das principais causas de morte em vacas de corte em pastagem em países do Hemisfério Sul, como Argentina, Austrália e Nova Zelândia. Aqui, revisamos a literatura sobre hipomagnesemia em bovinos de corte e descrevemos um surto no Uruguai. A doença ocorreu no final do outono, afetando vacas Aberdeen Angus e Aberdeen Angus x Hereford de 6-11 anos de idade em boas condições corporais, lactantes, multíparas e pastando em campos naturais que foram melhorados com fertilização e plantio de azevém e aveia. Aproximadamente 40 de 225 vacas foram afetadas e 24 (10,7%) morreram. O diagnóstico presuntivo de hipomagnesemia foi estabelecido com base na morte súbita, sinais clínicos neuromusculares agudos, dados epidemiológicos e a resposta à administração de Mg. O diagnóstico foi confirmado pela detecção de baixos níveis de Mg no soro (0,47-0,57mmol/L), humor vítreo (0,47-0,80mmol/L), humor aquoso (0,66mmol/L) e líquido cefalorraquidiano (0,59mmol/L). O componente mais importante da dieta correspondia a pastagens de azevém e aveia de rápido crescimento, as quais apresentaram altas concentrações de K (3,48%), N (4,38%) e P (0,94%), que sugerem hipomagnesemia secundária. Além disso, a relação K/(Ca+Mg) foi de 2,38 em forragens de azevém e aveia (valor de referência: 2,2) e 0,15 no solo (valor de referência: 0,09), que representam fatores de risco para hipomagnesemia. Em conclusão, a hipomagnesemia é uma causa importante de mortalidade em gado de corte em pastagens naturais melhoradas no Uruguai e pode ser facilmente prevenida pela correta suplementação sazonal de Mg.(AU)

A novel pathogenic mechanism for cerebellar lesions produced by Solanum bonariense in cattle.

Intoxication with Solanum bonariense in cattle causes cerebellar cortical degeneration with perikaryal vacuolation, axonal swelling, and death primarily of Purkinje cells, with accumulation of electron-dense residual storage bodies in membrane-bound vesicles. The pathogenesis of this disease is not fully understood. Previously, we proposed that inhibition of protein synthesis in Purkinje cells among other altered metabolic pathways could lead to cytoskeletal alterations, subsequently altering cell-specific axonal transport. In the present study, immunohistochemical and histochemical methods were used to identify neuronal cytoskeletal alterations and axonal loss, demyelination, and astrogliosis in the cerebellum of intoxicated bovines. Samples of cerebellum from 3 natural and 4 experimental cases and 2 control bovines were studied. Immunoreactivity against neurofilament (NF)-200KDa confirmed marked loss of Purkinje neurons, and phospho-NF protein, ß-tubulin, and affinity reaction against phalloidin revealed an altered perikaryal distribution of neuronal cytoskeletal proteins in the remaining Purkinje cells in intoxicated cattle. Reactive astrogliosis in every layer of the cerebellar cortex was also observed with anti-glial fibrillary acidic protein immunohistochemistry. In affected cattle, demyelination and axonal loss in the cerebellar white matter, as well as basket cell loss were demonstrated with Klüver-Barrera and Bielschowsky stains, respectively. Based on these results, we propose that neuronal cytoskeletal alterations with subsequent interference of the axonal transport in Purkinje cells may play a relevant role in the pathogenesis of this neurodegenerative disorder, and also that demyelination and axonal loss in the cerebellar white matter, as well as astrogliosis in the gray matter, likely occur secondarily to Purkinje cell degeneration and death.