The diatoms test in veterinary medicine: A pilot study on cetaceans and sea turtles

Experimental water injection into lungs using an animal model: Verification of the diatom concentration test to diagnose drowning

BACKGROUND

In forensic medicine, the diatom test is used to diagnose drowning. Drowning and postmortem immersion can be distinguished by calculating the ratio of diatom concentration in the lungs and drowning water (L/W ratio). However, this claim was based on the unproven hypothesis that diatoms may be concentrated in the lungs due to respiratory movements. This study was conducted to examine whether the L/W ratio increased with experimental water injection.

METHODS

A total of two experiments was performed using 22 non-drowned cat carcasses found on dry land. First, for the experimental postmortem immersion, we soaked seven whole-body cat carcasses in pond water for an hour. Second, the pond water was experimentally injected one or ten times into each harvested lung from seven and eight cats, respectively. In the diatom test, two diatom species (Aulacoseira ambigua and Discostella asterocostata) that were dominantly observed in pond water as well as other diatom species were counted separately. The L/W ratios of each cat were calculated. Univariate linear regression analysis was performed to demonstrate the association among L/W ratios and the three categories of the experiments. The L/W ratios of the two experiments were compared with those of drowning or postmortem immersion cases of humans or cats.

RESULTS

It was revealed that the clear L/W ratio differences between the three groups (experimental postmortem immersion<0.02, 1-injection < 0.2, 10-injection > 0.9 for all diatom counting) were with statistically significant as proven by the univariate regression analyses. In actual cases of cats and humans, L/W ratios were>0.4 for drowning and<0.04 for postmortem immersion.

CONCLUSION

The L/W ratio increased with multiple experimental water injections into the lungs, thereby verifying the validity of the diatom concentration test to diagnose drowning. The diatom test can be used to distinguish between drowning and postmortem immersion in humans and cats by calculating the L/W ratio.

Challenges in the Assessment of Bycatch: Postmortem Findings in Harbor Porpoises (Phocoena phocoena) Retrieved From Gillnets

Bycatch is considered one of the most significant threats affecting cetaceans worldwide. In the North Sea, bottom-set gillnets are a specific risk for harbor porpoises (Phocoena phocoena). Methods to estimate bycatch rates include on-board observers, remote electronic monitoring, and fishermen voluntarily reporting; none of these are systematically conducted. Additionally, necropsies of stranded animals can provide insights into bycatch occurrence and health status of individuals. There are, however, uncertainties when it comes to the assessment of bycatch in stranded animals, mainly due to the lack of diagnostic tools specific for underwater entrapment. We conducted a literature review to establish criteria that aid in the assessment of bycatch in small cetaceans, and we tested which of these criteria applied to harbor porpoises retrieved from gillnets in the Netherlands (n = 12). Twenty-five criteria were gathered from literature. Of these, "superficial incisions," "encircling imprints," and "recent ingestion of prey" were observed in the vast majority of our confirmed bycatch cases. Criteria like "pulmonary edema," "pulmonary emphysema," and "organ congestion" were also frequently observed, although considered unspecific as an indicator of bycatch. Notably, previously mentioned criteria as "favorable health status," "absence of disease," or "good nutritional condition" did not apply to the majority of our bycaught porpoises. This may reflect an overall reduced fitness of harbor porpoises inhabiting the southern North Sea or a higher chance of a debilitated porpoise being bycaught, and could result in an underestimation of bycatch rates when assessing stranded animals.

Development of 18S rRNA gene arrays for forensic detection of diatoms

Diatom test is the most commonly used method to diagnose drowning in forensic laboratories. However, microscopic examination and identification of diatom frustules is time-consuming and requires taxonomic expertise. At present, the identification of drowning is still a challenge in forensic casework. In this study, we developed a novel diatom microarray based on the detection of specific 18S rRNA gene fragments of diatom species. The array covers 169 diatom species which were documented as commonly found in a wide range of fresh waters in China. Diatom arrays were prepared from species specific oligonucleotide probes targeting to variable regions of the 18S rRNA gene. We also developed an auxiliary sample preparation method for isolation of diatom DNA from tissues, which enabled detection of diatom species in real forensic samples as well as environmental waters. We applied the diatom arrays to analyze six drowned cases and eight environmental samples. The diatom arrays showed much better sensitivity and more consistent results than those of the conventional SEM methods. We discovered major discrepancies between results generated by the diatom arrays and the routinely used SEM based diatom tests. We verified the results of our diatom arrays by species specific PCR and Sanger sequencing and found that the currently used SEM diatom test method has a serious deficiency in sensitivity due to high loss rate of frustules in the sample preparation procedure. We anticipate that the application of diatom arrays will transform current forensic practice of diagnosing drowning deaths.

Pathologic findings and causes of death of stranded cetaceans in the Canary Islands (2006-2012)

This study describes the pathologic findings and most probable causes of death (CD) of 224 cetaceans stranded along the coastline of the Canary Islands (Spain) over a 7-year period, 2006-2012. Most probable CD, grouped as pathologic categories (PCs), was identified in 208/224 (92.8%) examined animals. Within natural PCs, those associated with good nutritional status represented 70/208 (33.6%), whereas, those associated with significant loss of nutritional status represented 49/208 (23.5%). Fatal intra- and interspecific traumatic interactions were 37/208 (17.8%). Vessel collisions included 24/208 (11.5%). Neonatal/perinatal pathology involved 13/208 (6.2%). Fatal interaction with fishing activities comprised 10/208 (4.8%). Within anthropogenic PCs, foreign body-associated pathology represented 5/208 (2.4%). A CD could not be determined in 16/208 (7.7%) cases. Natural PCs were dominated by infectious and parasitic disease processes. Herein, our results suggest that between 2006 and 2012, in the Canary Islands, direct human activity appeared responsible for 19% of cetaceans deaths, while natural pathologies accounted for 81%. These results, integrating novel findings and published reports, aid in delineating baseline knowledge on cetacean pathology and may be of value to rehabilitators, caregivers, diagnosticians and future conservation policies.