The aetiology, prevalence and morbidity of outbreaks of photosensitisation in livestock: A review

Abstract

Background Photosensitisation is a clinical condition occurring in both humans and animals that causes significant injury to affected individuals. In livestock, outbreaks of photosensitisation caused by ingestion of toxic plants are relatively common and can be associated with significant economic loss. Objectives The agents that are most commonly implicated in outbreaks of photosensitisation have not been formally investigated on a global scale. To address this question, a systematic review of the literature was undertaken to determine the most common causative agents implicated in outbreaks of photosensitisation in livestock in Australia and globally, as well as the prevalence and morbidity of such outbreaks. Methods A systematic database search was conducted to identify peer-reviewed case reports of photosensitisation in livestock published worldwide between 1900 and April 2018. Only case reports with a full abstract in English were included. Non peer-reviewed reports from Australia were also investigated. Case reports were then sorted by plant and animal species, type of photosensitisation by diagnosis, location, morbidity and mortality rate and tabulated for further analysis. Results One hundred and sixty-six reports qualified for inclusion in this study. Outbreaks were reported in 20 countries. Australia (20), Brazil (20) and the United States (11) showed the highest number of peer-reviewed photosensitisation case reports from this analysis. Hepatogenous (Type III) photosensitisation was the most frequently reported diagnosis (68.5%) and resulted in higher morbidity. Panicum spp., Brachiaria spp. and Tribulus terrestris were identified as the most common causes of hepatogenous photosensitisation globally. Conclusions Hepatogenous photosensitisation in livestock represents a significant risk to livestock production, particularly in Australia, Brazil, and the United States. Management of toxic pastures and common pasture weeds may reduce the economic impact of photosensitisation both at a national and global level.

Hepatogenous Photosensitivity Outbreak after Coccidiosis in Grazing Holstein Steers

“…However, photosensitivity was not observed in these calves until 24 May, 17 days after exposure to fresh pasture. Early, clinical signs of photosensitivity are difficult to detect in the field, this likely leads to under-reporting of cases as suggested by Chen et al [ 7 ]. In this study, electric fencing was used to contain cattle; other than a salt-mineral feeder and water tank, calves did not have access to a physical object to scratch off sloughing skin.…”

“…Type 2 is rare and is caused by abnormal heme synthesis, resulting in accumulation of photodynamic metabolites [ 6 ]. Hepatogenous photosensitivity is the most common form [ 7 ], caused by the accumulation of phytoporphyrin (phylloerythrin) in dermal tissues [ 8 ]. Phylloerythrins are the metabolites of chlorophyll produced by microbial fermentation in ruminants [ 9 ] and are absorbed by the rumen, abomasum, and intestine, and are normally excreted in the bile [ 10 ].…”

“…Mortality and morbidity due to outbreaks of photosensitization are highly variable in the literature. Photosensitivity is known to occur in grazing cattle throughout the world, is sporadic, and is believed to be low occurrence, though that could be skewed by low reporting [ 7 ] and, likely, mild cases go unnoticed. Therefore, the purpose of this report is to share observations of an outbreak of photosensitivity that appeared suddenly, but also resolved quickly.…”

GBS Data Identify Pigmentation-Specific Genes of Potential Role in Skin-Photosensitization in Two Tunisian Sheep Breeds

“…Interestingly, as expected, five genomic regions among the seventeen identified in this study harbored key genes related to the pigmentation trait in sheep. This is not unexpected, given that the photosensitization can be the most severe in any portion of the animal exposed to sunlight that lacks a protective fleece, hair, or pigmentation [35][36][37]. The most significant genomic region under selection wasregion1, located on OAR 14, containing the Melanocortin 1 receptor MC1R gene, a key candidate gene for coat color pigmentation.…”

Shapes of pathology

“…In primary photosensitization (type I), the source of photodynamic pigment is plants or drugs (Mauldin & Peters-Kennedy 2016). As a result, herbivores are the most frequently affected species (Chen et al 2019). After absorption from the gastrointestinal tract, these agents travel via the portal circulation, are incompletely removed by the liver, and hematogenously spread to skin capillaries.…”