Technical note: A rapid, non-invasive method for measuring live or preserved insect specimens using digital image analysis

Effects of antibiotics ceftriaxone and levofloxacin on the growth of Protophormia terraenovae (Diptera: Calliphoridae)

Protophormia terraenovae is a colonizer of decomposing bodies and is known to cause pre-mortem myiasis as the female flies lay eggs in uncleaned wounds. In this study the effects of different concentrations of antibiotics levofloxacin and ceftriaxone on maggot development, weight, length, and mortality were examined. The maggot length and weight were significantly increased by therapeutical doses of levofloxacin and ceftriaxone. The maggot development time was significantly decreased in every levofloxacin treatment compared to the control. The time to start pupation was significantly increased in the control compared to the antibiotic treatments. Levofloxacin significantly increased the survivability of the maggots. Every levofloxacin treatment significantly improved the rearing conditions for the maggots. Reaching the third instar was delayed by 24 h in the control compared to the Levo 3.57 treatment. The Pupation in the control was delayed by an average of 48 h compared to the Levo 3.57 treatment. The significantly reduced development time of the maggots in the antibiotic treatments might lead to an overestimation of the post-mortem interval and therefore an incorrect time of death determination. The improved rearing conditions may be an indication of the potential of a combined application of antibiotics and maggot therapy.

Identification of tungiasis infection hotspots with a low-cost, high-throughput method for extracting Tunga penetrans (Siphonaptera) off-host stages from soil samples-An observational study

BACKGROUND

The sand flea, Tunga penetrans, is the cause of a severely neglected parasitic skin disease (tungiasis) in the tropics and has received little attention from entomologists to understand its transmission ecology. Like all fleas, T. penetrans has environmental off-host stages presenting a constant source of reinfection. We adapted the Berlese-Tullgren funnel method using heat from light bulbs to extract off-host stages from soil samples to identify the major development sites within rural households in Kenya and Uganda.

METHODS AND FINDINGS

Simple, low-cost units of multiple funnels were designed to allow the extraction of >60 soil samples in parallel. We calibrated the method by investigating the impact of different bulb wattage and extraction time on resulting abundance and quality of off-host stages. A cross-sectional field survey was conducted in 49 tungiasis affected households. A total of 238 soil samples from indoor and outdoor living spaces were collected and extracted. Associations between environmental factors, household member infection status and the presence and abundance of off-host stages in the soil samples were explored using generalized models. The impact of heat (bulb wattage) and time (hours) on the efficiency of extraction was demonstrated and, through a stepwise approach, standard operating conditions defined that consistently resulted in the recovery of 75% (95% CI 63-85%) of all present off-host stages from any given soil sample. To extract off-host stages alive, potentially for consecutive laboratory bioassays, a low wattage (15-25 W) and short extraction time (4 h) will be required. The odds of finding off-host stages in indoor samples were 3.7-fold higher than in outdoor samples (95% CI 1.8-7.7). For every one larva outdoors, four (95% CI 1.3-12.7) larvae were found indoors. We collected 67% of all off-host specimen from indoor sleeping locations and the presence of off-host stages in these locations was strongly associated with an infected person sleeping in the room (OR 10.5 95% CI 3.6-28.4).

CONCLUSION

The indoor sleeping areas are the transmission hotspots for tungiasis in rural homes in Kenya and Uganda and can be targeted for disease control and prevention measures. The soil extraction methods can be used as a simple tool for monitoring direct impact of such interventions.

Effects of antibiotics ceftriaxone and levofloxacin on the growth of Lucilia sericata (Diptera: Calliphoridae)

Lucilia sericata is one of the most studied species in forensic entomology due to its widespread distribution, forensic importance as well as medical use. The growth and development stage of maggots is often used to determine the post-mortem interval in forensic cases. L. sericata can cause myiasis in humans who are not able to maintain personal hygiene due to age or medical condition and can therefore be used to determine the time period of neglect. The influence of the temperature on the maggot development has been examined in various studies. Different examinations on the effects of toxic substances on the maggot development and survival have been conducted in order to test the influence and resulting deviations. In this study, the effects of different therapeutical doses of the antibiotics ceftriaxone and levofloxacin were examined on L. sericata in order to determine and compare deviations in maggot development and survival. The used antibiotics did not significantly influence the maggot weight and length. A significant delay in the time of pupation has been determined in the treatments with high concentrations of levofloxacin. The mortality was significantly increased in all treatments with antibiotics compared to the control, whereby the survivability of all treatments remained over 80%. Because of the high doses needed to produce an effect, we concluded that an overestimation of the post-mortem interval is unlikely but higher antibiotic concentrations or possible interactions with other medications could increase the maggot development time.

Effects of antibiotics ceftriaxone and levofloxacin on the growth of Calliphora vomitoria L. (Diptera: Calliphoridae) and effects on the determination of the post-mortem interval

The determination of the post-mortem interval (PMI) is one of the main tasks of forensic entomology, where growth and stages of development of arthropods are used for PMI determination. It is well acknowledged that maggot development is significantly influenced by temperature. Attention has also been paid to the microbial populations of the cadaver, because toxic substances contained in the substrate can influence the microorganisms and affect arthropods growth and development. However, little is known about the influence of antibiotics taken during lifetime of a person on insect development after that persons death. The aim of this study was to test the hypothesis that the antibiotics ceftriaxone and levofloxacin cause inhibition of growth and delay of pupation of the blow fly Calliphora vomitoria, which would then lead to an incorrect determination of the post-mortem interval in forensic cases. It was found that maggot development was delayed by levofloxacin mixed in minced pork, where a mixture of both antibiotics increased this effect. The maggot growth in the samples with ceftriaxone was not delayed. Pupation was delayed in treatments with a mixture of both antibiotics. The mortality was reduced by separate or combined application of ceftriaxone and levofloxacin, which we attribute to a bactericidal effect of the antibiotics on maggot pathogens. Depending on the concentration of the antibiotics, an underestimation of the post-mortem interval between 24 and 48 h could be suspected. We conclude that antibiotics need to be considered if instar stages are to be used to determine the PMI and that some antibiotics may improve the breeding conditions of maggots.

Metrological framework for selecting morphological characters to identify species and estimate developmental maturity of forensically significant insect specimens

Accurate age estimates of immature necrophagous insects associated with a human or animal body can provide evidence of how long the body has been dead. These estimates are based on species-specific details of the insects’ aging processes, and therefore require accurate species identification and developmental stage estimation. Many professionals who produce or use identified organisms as forensic evidence have little training in taxonomy or metrology, and appreciate the availability of formalized principles and standards for biological identification. Taxonomic identifications are usually most readily and economically made using categorical and qualitative morphological characters, but it may be necessary to use less convenient and potentially more ambiguous characters that are continuous and quantitative if two candidate species are closely related, or if identifying developmental stages within a species. Characters should be selected by criteria such as taxonomic specificity and metrological repeatability and relative error. We propose such a hierarchical framework, critique various measurements of immature insects, and suggest some standard approaches to determine the reliability of organismal identifications and measurements in estimating postmortem intervals. Relevant criteria for good characters include high repeatability (including low scope for ambiguity or parallax effects), pronounced discreteness, and small relative error in measurements. These same principles apply to individuation of unique objects in general.

Key points

Metrological rigour can increase in forensic entomology by selecting measurements based on their metrological qualities.

Selection of high-quality features for morphological identification of organisms should consider these criteria: (1) pronounced discreteness of features (minimising group overlap or maximizing interval); (2) high repeatability of assessment (such as symmetrical width rather than asymmetrical length); (3) small relative error in measurement (selecting the physically largest continuous rigid feature for measurement).

These metrological principles also apply to individuation of unique objects in general.