Left shift and toxic change in heterophils and neutrophils of non-mammalian vertebrates: A comparative review, image atlas, and practical considerations

Immune and endocrine alterations at the early stage of inflammatory assemblage in toads after stimulation with heat-killed bacteria (Aeromonas hydrophila)

The red-leg syndrome in amphibians is a condition commonly associated with the bacteria Aeromonas hydrophila and has led to population declines. However, there is little information concerning the inflammatory assemblage in infected anurans. We evaluated immune and endocrine alterations induced by stimulation with heat-killed A. hydrophila injected in Rhinella diptycha toads. Control animals were not manipulated, while the others were separated into groups that received intraperitoneal injection of 300 μl of saline or heat-killed bacteria: groups A1 (3 × 107 cells), A2 (3 × 108 cells), and A3 (3 × 109 cells). Animals were bled and euthanized six hours post-injection. We evaluated neutrophil: lymphocyte ratio (NLR), plasma bacterial killing ability (BKA), testosterone (T), melatonin (MEL), and corticosterone (CORT) plasma levels. Heat-killed A. hydrophila increased CORT and NLR, and decreased MEL, especially at higher concentrations. There was no effect of treatment on T and BKA. We then selected the saline and A3 groups to conduct mRNA expression of several genes including glucocorticoid receptor (GR), toll-like receptor-4 (TLR-4), interferon-γ (IFN-γ), interleukin (IL)-1β, IL-6, and IL-10. We found higher expression of IL-6, IL-1β, IL-10, and IFN-γ in group A3 compared to the saline group. These results indicate the beginning of an inflammatory assemblage, notably at the two highest concentrations of bacteria, and give a better understanding of how anurans respond to an infection within an integrated perspective, evaluating different physiological aspects. Future studies should investigate later phases of the immune response to elucidate more about the inflammation in amphibians challenged with A. hydrophila.

Environmental temperature influences ophidiomycosis progression and survival in experimentally challenged prairie rattlesnakes (Crotalus viridis)

Ophidiomycosis is a prevalent and intermittently pervasive disease of snakes globally caused by the opportunistic fungal pathogen, Ophidiomyces ophidiicola. Host response has yet to be fully explored, including the role of temperature in disease progression and hematologic changes. This study enrolled twelve adult prairie rattlesnakes (Crotalus viridis) in an experimental challenge with O. ophidiicola at two temperatures, 26°C (n = 6) and 20°C (n = 6). Each temperature cohort included four inoculated and two control snakes. Assessments involving physical exams, lesion swabbing, and hematology were performed weekly. Differences were observed between inoculated and control snakes in survival, behavior, clinical signs, ultraviolet (UV) fluorescence, hematologic response, and histologic lesions. All inoculated snakes held at 20°C were euthanized prior to study end date due to severity of clinical signs while only one inoculated animal in the 26°C trial met this outcome. In both groups, qPCR positive detection preceded clinical signs with regards to days post inoculation (dpi). However, the earliest appearance of gross lesions occurred later in the 20°C snakes (20 dpi) than the 26°C snakes (13 dpi). Relative leukocytosis was observed in all inoculated snakes and driven by heterophilia in the 20°C snakes, and azurophilia in the 26°C group. Histologically, 20°C snakes had more severe lesions, a lack of appropriate inflammatory response, and unencumbered fungal proliferation and invasion. In contrast, 26°C snakes had marked granulomatous inflammation with encapsulation of fungi and less invasion and dissemination. The results of this study identified that O. ophidiicola-infected rattlesnakes exposed to lower temperatures have decreased survival and more robust hematologic change, though minimal and ineffective inflammatory response at site of infection. Ophidiomycosis is a complex disease with host, pathogen, and environmental factors influencing disease presentation, progression, and ultimately, survival. This study highlighted the importance of temperature as an element impacting the host response to O. ophidiicola.

The Impacts of Transdermal Application of Corticosterone on Toad (Rhinella icterica) Immunity

Recent studies have shown that acute physiological increases in endogenous glucocorticoid levels have immunostimulatory effects. Although post-acute stress immunosuppressive effects have also been described, the difference between enhancing and suppressing the immune response seems mediated by the stressor's duration, intensity, and the immune component under analysis. To elicit physiologically relevant corticosterone levels that can be found in Rhinella icterica toads after stressful events (e.g., restraint or captivity) and understand how acute increased glucocorticoid levels of different intensities affect corticosterone and testosterone plasma levels and immune parameters (in vitro plasma bacterial killing ability, neutrophil-to-lymphocyte ratio, and in vivo phagocytosis of peritoneal leukocytes), we submitted toads to the transdermal application of two corticosterone doses (1 and 10 μg). Corticosterone transdermal application increased corticosterone plasma levels with different intensities: 3 times for 1 μg and fourteen times for 10 μg, compared to the vehicle, and the neutrophil-to-lymphocyte ratio increased regardless of the corticosterone dose. However, there was no effect on testosterone levels and bacterial killing ability. Interestingly, both corticosterone doses promoted immunosuppression, decreasing peritoneal leukocytes' phagocytosis activity by 60% for toads receiving the dose of 1µg and 40% for those receiving 10 μg. Our results show the complexity of the relationship between increased corticosterone levels and immunomodulation. The different corticosterone doses promoted increases of distinct magnitudes in corticosterone plasma levels, with the less intense increase in corticosterone levels generating greater cell-mediated immunosuppression. Future studies using different corticosterone doses to achieve and compare physiological vs. pharmacological hormone levels are imperative to understanding these interrelationships between corticosterone and immune response.

Diagnostic Clinical Pathology of Tortoises

Clinicopathologic evaluation of terrestrial tortoises is useful for health assessment and monitoring. There are specific considerations when evaluating data from these species, including sex, age, time of year/season, reproductive status, diet, captive versus wild, geographic location, methodology, and anticoagulant. The authors describe sample collection, hematology, biochemistry, and urinalysis features of terrestrial tortoises and discuss clinical relevance.

Island of misfit tortoises: waif gopher tortoise health assessment following translocation

Translocation, the intentional movement of animals from one location to another, is a common management practice for the gopher tortoise (Gopherus polyphemus). Although the inadvertent spread of pathogens is a concern with any translocation effort, waif tortoises-individuals that have been collected illegally, injured and rehabilitated or have unknown origins-are generally excluded from translocation efforts due to heightened concerns of introducing pathogens and subsequent disease to naïve populations. However, repurposing these long-lived animals for species recovery is desirable when feasible, and introducing waif tortoises may bolster small populations facing extirpation. The objective of this study was to assess the health of waif tortoises experimentally released at an isolated preserve in Aiken County, SC, USA. Our assessments included visual examination, screening for 14 pathogens using conventional or quantitative polymerase chain reaction (qPCR) and haematological evaluation. Of the 143 individuals assessed in 2017 and 2018, most individuals (76%; n = 109 of 143) had no overt clinical evidence of disease and, when observed, clinical findings were mild. In both years, we detected two known tortoise pathogens, Mycoplasma agassizii and Mycoplasma testudineum, at a prevalence of 10.2-13.9% and 0.0-0.8%, respectively. Additionally, we found emydid Mycoplasma, a bacterium commonly found in box turtles (Terrapene spp.), in a single tortoise that showed no clinical evidence of infection. The presence of nasal discharge was an important, but imperfect, predictor of Mycoplasma spp. infection in translocated tortoises. Hemogram data were comparable with wild populations. Our study is the first comprehensive effort to assess pathogen prevalence and hemogram data of waif gopher tortoises following translocation. Although caution is warranted and pathogen screening necessary, waif tortoises may be an important resource for establishing or augmenting isolated populations when potential health risks can be managed.

Electrolyte imbalances and dehydration play a key role in Batrachochytrium salamandrivorans chytridiomycosis

Introduction

One of the most important emerging infectious diseases of amphibians is caused by the fungal pathogen Batrachochytrium salamandrivorans (Bsal). Bsal was recently discovered and is of global concern due to its potential to cause high mortality in amphibians, especially salamander species. To date, little has been reported on the pathophysiological effects of Bsal; however, studies of a similar fungus, B. dendrobatidis (Bd), have shown that electrolyte losses and immunosuppression likely play a key role in morbidity and mortality associated with this disease. The goal of this study was to investigate pathophysiological effects and immune responses associated with Bsal chytridiomycosis using 49 rough-skinned newts (Taricha granulosa) as the model species.

Methods

Taricha granulosa were exposed to a 1 × 107 per 10 mL dose of Bsal zoospores and allowed to reach various stages of disease progression before being humanely euthanized. At the time of euthanasia, blood was collected for biochemical and hematological analyses as well as protein electrophoresis. Ten standardized body sections were histologically examined, and Bsal-induced skin lesions were counted and graded on a scale of 1-5 based on severity.

Results

Results indicated that electrolyte imbalances and dehydration induced by damage to the epidermis likely play a major role in the pathogenesis of Bsal chytridiomycosis in this species. Additionally, Bsal-infected, clinically diseased T. granulosa exhibited a systemic inflammatory response identified through alterations in complete blood counts and protein electrophoretograms.

Discussion

Overall, these results provide foundational information on the pathogenesis of this disease and highlight the differences and similarities between Bsal and Bd chytridiomycosis.