Rodent Pediatrics

This article reviews the development, hand-rearing, feeding, housing, and social behavior of common pet rodent species (rats, mice, hamsters, gerbils, guinea pigs, chinchillas, and degus). In addition, common gastrointestinal, respiratory, cardiovascular, dermatologic, musculoskeletal, neurologic, and ophthalmic disorders in pediatric pet rodents are reviewed. Preventative care and indications for spaying and neutering are discussed.

Nutritional Physiology and Feeding of Companion Rodents

Rodents represent a diverse group that shares commonalities in approaches to dietary management. Nutritional management of companion rodents must diverge from laboratory animal management, and must also consider the importance of a healthy gastrointestinal microbiome. Published requirements must be applied appropriately to species, life stage, and body condition management. Common nutritional health concerns include digestive-tract dysbiosis, gastrointestinal stasis, dental malocclusion, obesity, and hypervitaminosis D. Health issues may be avoided or alleviated through proactive management of appropriate feedstuffs in correct proportion, avoidance of most feeds made specifically for laboratory rodents, and emphasis on promoting healthy activity through environmental enrichment.

High Prevalence of Hymenolepis (Rodentolepis) nana in Amateur Breeding Facilities of Chinchillas (Chinchilla lanigera) and Sugar Gliders (Petaurus breviceps) from Italy

PURPOSE

Hymenolepis (Rodentolepis) nana is an enteric tapeworm globally widespread in wild and captive rodents. The survey was carried out in three chinchilla breeding facilities and in one sugar glider breeding facility in Central and Southern Italy.

METHODS

One hundred and four chinchilla fecal pools and 40 sugar glider fecal pools were collected from cages housing breeding pairs or females with their offspring. Fecal samples were examined with a qualitative and quantitative copromicroscopical approach. Hymenolepis eggs were identified based on morphological and morphometrical features, and the average number of eggs per gram (EPG) of feces was estimated.

RESULTS

Hymenolepis nana eggs were detected in 39.42% of chinchilla samples with an average of 16.33 EPG; whereas, all of the sugar glider samples tested positive with an average of 454.18 EPG. Neither helminth eggs nor protozoan cysts/oocysts were detected in any of the breeding facilities.

CONCLUSION

The results clearly show a diffuse parasitism in both chinchillas and sugar gliders, and should be taken into consideration given the rising popularity of these two pet species combined with the zoonotic complications presented by H. nana.

A comparison of commercially available feeds for rabbits, guinea pigs, chinchillas and degus with evidence of their diet and feeding behaviour in natural habitats

INTRODUCTION

A large variety of pet feeds is commercially available for pet herbivores; these feeds may differ in nutrient composition from the natural diet, and may trigger different feeding behaviours than observed in natural habitats. Here, we surveyed literature on the natural diet and activity budget of rabbits (Oryctolagus cuniculus), guinea pigs (Cavia porcellus), chinchilla (Chinchilla lanigera) and degus (Octodon degus), as well as 260 compound feeds commercially available for these species between 1982 and 2020. The species are classified as herbivores, with available data on natural diets suggesting a crude fibre (CF) level of approximately 250 g/kg dry matter (DM), natural feeding activity at a magnitude of 4-7 h per day, with distinctively shorter feeding when fed on compound pet feeds. Only for a minority of feeds did the first 5 listed ingredients not include a starchy ingredient, or only ingredients not considered suitable for human consumption. The percentage of feeds whose CF level was less than 150 g/kg DM was 22 % for production rabbits, 18 % for pet rabbits, 26 % for guinea pigs, 18 % for chinchillas and 14 % for degus; in other words, a majority of currently marketed products have CF levels in accord with published recommendations, even if that means a discrepancy to natural diets. Screening the producers' feeding instructions suggests they should generally not be followed uncritically. No temporal trends in the CF levels of these diets was evident. There is no consensus whether only products resembling natural diet items should be included in pet feeds, or whether vegetable byproducts not edible by humans should also be included. The observed practice of pet feed composition largely did not follow either concept, questioning the general rationale of pet feed composition. Whole forage like hay is recommended as the main diet component for these species, and 76 % of pet feed products noted that hay should be fed in the feeding instructions.

Phacoemulsification in a chinchilla (Chinchilla lanigera)

Background

A cataract is one of the underlying causes of blindness in animals. Phacoemulsification is the standard procedure in cataract surgery for humans and animals. This procedure has been used to restore vision in cataracts in a variety of animals. However, this technique is difficult in very small animals, such as rodents, due to their small eyes.

Case Description

A 4-year-old male domestic chinchilla was presented with cloudiness in the lenses for 1 month. The ophthalmic examination revealed cataracts (oculus uterque: both eyes). Positive dazzle reflex oculus sinister; left eye (OS) and negative reflex oculus dexter; right eye (OD) were noted. The electroretinography was low amplitude OS whereas a flat waveform presented OD. In this case, cataract surgery was performed using phacoemulsification without intraocular lens implantation OS. Postoperative, the chinchilla was alert and could jump on and jump off the ledge in a house. When the veterinarian approached closely to OS, the chinchilla displayed an erect body posture and open eyes, whereas the chinchilla was ignored when the veterinarian doing the same OD. The chinchilla was alert and had improved vision observe by this chinchilla can jump on and jump off the ledge in his house throughout the follow-up period 18 months later.

Conclusion

In this chinchilla, phacoemulsification was successfully performed and resulted in better overall vision. The chinchilla was alert and could jump on and jump off the ledge in a house after cataract surgery throughout the follow-up period of 18 months.

Rodent Dermatology

This article reviews the most common dermatologic conditions of the pet rodent population, including the prevalence, clinical signs, diagnosis, and treatment recommendations.

Hearing protection and damage mitigation in Chinchillas exposed to repeated low-intensity blasts

Repeated exposures to blast overpressure (BOP) introduce hearing complaints in military service members even with the use of hearing protection devices (HPDs). Although epidemiology and animal studies have been performed to investigate the damage formation mechanism of blast-induced hearing damage, there is still a lack of understanding and therapeutic solutions, especially for HPD-protected ears. Recent studies revealed the potential therapeutic function of liraglutide, a glucagon-like peptide-1 receptor agonist, to facilitate post-blast hearing restoration in chinchillas. This study is a continuation and summary of the previous studies performed by Jiang et al. (2021, 2022) to investigate the damage mitigation function of liraglutide treatment in chinchillas with open and protected ears after repeated low-intensity blast exposures within 28 days of observation. Chinchillas were divided into six experimental groups: pre-blast treatment, post-blast treatment, and blast control with ears open or protected by earplug (EP). All animals were exposed to six consecutive blasts at the level of 3-5 psi (21-35 kPa) on Day 1. Hearing function tests including auditory brainstem response (ABR), distortion product otoacoustic emission (DPOAE), and middle latency response (MLR) were performed on Day 1 (pre- and post-blast) and Days 4, 7, 14, and 28 after blast exposure. Results indicated that the damage mitigation function of the liraglutide treatment in the open-ear chinchillas was reflected by the significantly lower ABR threshold shifts in the drug treatment groups than in the blast controls. In EP groups, the higher ABR wave I/V ratio and lower MLR amplitude observed in the drug-treated chinchillas suggested that the post-blast hyperactivities in the auditory system might be potentially ameliorated by the liraglutide treatment. The 28-day-long experiment showed the effect of liraglutide treatment increased with time in both open and EP groups. This study demonstrated that the use of HPDs prevented the blast-induced complications in the middle ear and reduced the damage caused in the central auditory system. The liraglutide treatment showed an effect increasing with time and different outcomes in open and EP chinchillas. This innovation in the animal model of chinchilla provides insights to investigate subtle changes in the higher-level structures of the auditory system.

Cochlear tuning and the peripheral representation of harmonic sounds in mammals

Albert Feng was a prominent comparative neurophysiologist whose research provided numerous contributions towards understanding how the spectral and temporal characteristics of vocalizations underlie sound communication in frogs and bats. The present study is dedicated to Al's memory and compares the spectral and temporal representations of stochastic, complex sounds which underlie the perception of pitch strength in humans and chinchillas. Specifically, the pitch strengths of these stochastic sounds differ between humans and chinchillas, suggesting that humans and chinchillas may be using different cues. Outputs of auditory filterbank models based on human and chinchilla cochlear tuning were examined. Excitation patterns of harmonics are enhanced in humans as compared with chinchillas. In contrast, summary correlograms are degraded in humans as compared with chinchillas. Comparing summary correlograms and excitation patterns with corresponding behavioral data on pitch strength suggests that the dominant cue for pitch strength in humans is spectral (i.e., harmonic) structure, whereas the dominant cue for chinchillas is temporal (i.e., envelope) structure. The results support arguments that the broader cochlear tuning in non-human mammals emphasizes temporal cues for pitch perception, whereas the sharper cochlear tuning in humans emphasizes spectral cues.

No Reduction in the 226-Hz Probe Tone Acoustic Reflex Amplitude Following Severe Inner Hair Cell Loss in Chinchillas

The relationship between the middle ear acoustic reflex (AR) and inner hair cell (IHC) loss is currently unknown. Given that IHC are believed to convey nearly all acoustic information to the central auditory nervous system, it has been assumed that loss of IHC would significantly impact the AR. To evaluate this relationship, we assessed the presence and amplitude of the AR in chinchillas before and after treatment with carboplatin, an anticancer drug that reliably and selectively destroys IHC in this species. Baseline measures of hearing sensitivity, including auditory brainstem response (ABR) thresholds and distortion product otoacoustic emissions (DPOAE), were assessed and then re-evaluated following carboplatin treatment. Post-carboplatin ABR thresholds and DPOAE were found to be unchanged or slightly elevated; results were consistent with published reports. Our main hypothesis was that loss of IHC would abolish the reflex or significantly reduce its amplitude. Contrary to our hypothesis, the ipsilateral 226-Hz AR continued to be reliably elicited following carboplatin treatment. Post-mortem histological analysis confirmed significant IHC loss (65-85 %), but no measurable loss of outer hair cells (OHCs). Given that loss of IHC alone does not significantly reduce the 226-Hz AR, our results suggest that few IHC are needed to maintain the 226-Hz AR response. These results suggest additional studies are needed to better understand the role of IHC in the reflex arc, present opportunities to further study the reflex pathway, and could change how we use the clinical AR as a potential diagnostic tool for IHC dysfunction, including those related to IHC synaptopathy.

Cardiology in Rodents, Rabbits, and Small Exotic Mammals-Diagnostic Workup

The incidence of cardiac diseases in pet rabbits and rodents increased over the past decade as these species live longer and diagnostics methods are more precise to diagnose heart diseases even in small-sized animals. The article summarizes diagnostics of cardiac diseases in selected exotic companion mammals, particularly in rabbits, guinea pigs, chinchillas, and rats. The emphasis of the paper is given on clinical examination, thoracic radiography, electrocardiography, and echocardiography.

Current topics in hearing research: Deafferentation and threshold independent hearing loss

Hearing research findings in recent years have begun to change how we think about hearing loss and how we consider the risk of auditory damage from noise exposure. These findings include evidence of noise-induced cochlear damage in the absence of corresponding permanent threshold elevation or evidence of hair cell loss. Animal studies in several species have shown that noise exposures that produce robust but only temporary threshold shifts can permanently damage inner hair cell synaptic ribbons. This type of synaptic degeneration has also been shown to occur as a result of aging in animals and humans. The emergence of these data has motivated a number of clinical studies aimed at identifying the perceptual correlates associated with synaptopathy. The deficits believed to arise from synaptopathy include poorer hearing in background noise, tinnitus and hyperacusis (loudness intolerance). However, the findings from human studies have been mixed. Key questions remain as to whether synaptopathy reliably produces suprathreshold perceptual deficits or whether it serves as an early indicator of auditory damage with suprathreshold deficits emerging later as a function of further cochlear damage. Here, we provide an overview of both human and animal studies that explore the relationship among inner hair cell damage, including loss of afferent synapses, auditory thresholds, and suprathreshold measures of hearing.

Concomitant Congenital Diaphagmatic Hernia (CDH) and bilateral bacterial glomerulonephritis in a pet chinchilla (Chinchilla lanigera)

Background

The domestic chinchilla has been descended from Chinchilla lanigera (long-tailed Chinchilla) or Chinchilla chinchilla (short-tailed Chinchilla). Both species of chinchilla are currently listed as endangered by the IUCN Red List of Threatened Species. Over the past 20 years, they have spread as pets and overall knowledge about their care is improving. The present case report describes a congenital diaphragmatic hernia in a Chinchilla lanigera.

Case presentation

A 1-year-old, 420 g female chinchilla (Chinchilla lanigera) was presented for clinical examination due to 2 days haematuria episodes and anorexia. A complete haematological analysis was performed, showing a moderate neutrophilia and severe renal involvement. X-rays showed severe intestinal meteorism affecting mostly the cecum, and a soft tissue density mass with translucent areas located in the caudal thorax, making it hard to distinguish the cardiac silhouette. A barium swallow (barium sulfate) was performed and after 20 min, radiograms were performed again, showing part of the stomach dislocated in thorax. Ultrasound was also carried out, confirming the partial stomach herniation into the thoracic cavity and a severe nephropathy. The patient was euthanized according to the owner’s wish and a complete necropsy was performed. The diagnosis was congenital diaphragmatic hernia concomitant to a severe bilateral bacterial glomerulonephritis.

Discussion and conclusions

Diaphragmatic hernias can be either congenital or acquired. About CDHs in pet chinchillas, literature is still lacking. In this patient there was no history of previous traumas. No scar tissue or thickening involved margins of the pathological diaphragm window at the necropsy, supporting the hypothesis of a congenital defect. Glomerulonephritis most often results from immune-mediated mechanisms, generally after the deposition of soluble immune complexes within the glomeruli. This mechanism is favoured by a prolonged antigenemia that could occur during specific viral infections, chronic bacterial infections, chronic parasitism, autoimmune diseases and neoplasia. Few cases of nephritis are described in chinchillas (Chinchilla lanigera), mostly related to bacterial sepsis or less commonly involving fungi. The evidence of bacterial aggregates in kidneys at the histopathology, confirmed the infective aetiology. No relationship between the diaphragmatic hernia and glomerulonephritis was found in this report.

Respiratory Diseases in Guinea Pigs, Chinchillas and Degus

The diagnosis and treatment of respiratory disease in pet guinea pigs, chinchillas, and degus still face profoundly serious challenges owing to their relatively small size, conspicuous clinical signs, difficulty for sampling, and insufficient scientific evidence to correlate signs and particular pathologies. This article is intended to summarize the available information on the relevant anatomy, physiology, and respiratory pathology in these species.

Abnormal Repetitive Behaviors and Self-Mutilations in Small Mammals

Self-mutilation and abnormal repetitive behaviors in small mammals are challenging conditions for veterinary practitioners. The etiology may be difficult to identify, and the treatment is often unrewarding unless the specific underlying cause can be found. Reinforcement of the abnormal behavior may also complicate the treatment. However, medical causes, including painful conditions, should be investigated thoroughly. Owing to the small blood volume of many small exotic mammals and the associated risk of hypovolemia in case of hemorrhage, an hospitalization with potent multimodal analgesia and physical barriers to prevent self-mutilation is often warranted. Psychogenic drugs may be useful in some cases.

Senescent cells in rabbit, nutria and chinchilla testes-Results from histochemical and immunohistochemical studies

Rabbit, nutria and chinchilla testes were evaluated to compare testicular cellular senescence. There were no major species-specific differences in structure of either seminiferous tubules or interstitial tissue. There, however, were occasional abnormalities in seminiferous tubule structure with there being multinucleated and exfoliated cells present in rabbit testes. Furthermore, there were seminiferous tubules without a lumen that were filled with premeiotic/meiotic cells in nutria; and tubules with vacuolization with there being no post-meiotic cells in chinchillas. There were no differences in distribution or content of acids, total proteins and polysaccharides in the testis of any of the three species. Results using comparative immunohistochemistry procedures indicated the testes contained a few senescent cells in seminiferous tubules with typical morphology and there was a large number of senescent cells in seminiferous tubules of nutrias and chinchillas that had an abnormal structure (P <0.001). Compared to rabbit testes, in which there was the least number of senescent cells in seminiferous tubules, there was a greater abundance of senescence markers in both nutria and chinchilla testes (P < 0.05; P < 0.001, respectively). Furthermore, there were small abundances of caspase 3 and LC3 in the testes of all species. In chinchilla testes, there was a lesser concentration of cholesterol (P < 0.001) and testosterone compared with the other species. Cellular senescence in testes, therefore, can be assessed by detection of morpho-functional disorders of the testis of the three species evaluated in the present study.

Mass spectrometry imaging of blast overpressure induced modulation of GABA/glutamate levels in the central auditory neuraxis of Chinchilla

Acoustic trauma damages inner ear neural structures including cochlear hair cells which result in hearing loss and neurotransmitter imbalances within the synapses of the central auditory pathway. Disruption of GABA/glutamate levels underlies, tinnitus, a phantom perception of sound that persists post-exposure to blast noise which may manifest in tandem with acute/chronic loss of hearing. Many putative theories explain tinnitus physiology based on indirect and direct assays in animal models and humans, although there is no comprehensive evidence to explain the phenomenon. Here, GABA/glutamate levels were imaged and quantified in a blast overpressure model of chinchillas using Fourier transform ion cyclotron resonance mass spectrometry imaging. The direct measurement from whole-brain sections identified the relative levels of GABA/glutamate in the central auditory neuraxis centers including the cochlear nucleus, inferior colliculus, and auditory cortex. These preliminary results provide insight on the homeostasis of GABA/glutamate within whole-brain sections of chinchilla for investigation of the pathomechanism of blast-induced tinnitus.

[Inner hair cells loss by carboplatin and the changes of cochlear compound action potential in chinchillas]

Objective: To measure the cochlear compound action potential (CAP) and the densities of hair cells (HCs) along the whole length of the basilar membrane (BM) in adult chinchillas. And to investigate the relationship between the severity of inner hair cells (IHCs) loss and the changes of CAP by using carboplatin-cochlear lesion model. Methods: Totally 18 chinchillas were recruited after ontological evaluation. They were randomly divided into three groups (with 6 subjects in each), A: control, B and C: legion groups treated with one or two shot(s) of carboplatin respectively (76 mg/kg in one shot, i.p., one-week interval between the two shots). Endpoint tests were performed 30 days after the carboplatin treatment in groups B and C, and matched time in group A. A sliver-ball electrode was placed into round window niche via hypotympanic approach in anesthetized chinchilla. CAP was measured in response to clicks and tone burst of 0.5, 1, 2, 4, 8, 16 kHz respectively under anesthesia. CAP amplitudes and thresholds were measured and compared across the groups. After the recording, the whole cochlea surface preparation was made and the HCs were stained in histochemistry against substrate of succinate dehydrogenase (SDH). Images were taken with high-resolution digital camera under light microscope and across the whole cochlea. The length of the basilar membrane (BM) and the number of both IHCs and OHCs were counted. The HC density was calculated as the number of HCs per 10% BM length. Results: The CAP thresholds were (7.1±2.6), (25.4±5.0), (24.6±5.4), (10.4±5.0), (0.4±1.4), (4.2±6.3) and (17.1±14.1) dB SPL (from 6 subjects in group A, n=12 ears) corresponding to stimuli of Click and 0.5, 1, 2, 4, 8, 16 kHz tone bursts respectively. The total number of cochlear HCs were measured as (8 936±643) (x±s) and the average length of the BMs was (17.73±1.012) mm from the six subjects in the group A (n=12 ears). The HC density was found to be varied slightly across the BM. There was no significant CAP threshold difference between the control (group A) and the group B, which received one shot of carboplatin. However, the maximal CAP amplitude was reduced by 40% in the group B and compared with group A. Correspondingly, approximately 40% loss of IHCs were seen. In contrast, a significant CAP threshold shift was seen in subjects receiving two shots of carboplatin (group C), which was accompanied by a loss of 90% IHCs. Conclusions: The CAP thresholds of adult chinchillas show typical open-V shape with the lowest values at 2, 4, and 8 kHz. IHC loss by carboplatin in certain degree is well correlated with CAP amplitude reduction, but does not change the threshold when inner hair cell loss reaches 40%, however, if inner hair cell loss exceeds 80%, the threshold shift of CAP will be inevitable.

Geriatric Care of Rabbits, Guinea Pigs, and Chinchillas

Specialized veterinary care needed for geriatric rabbits, guinea pigs, and chinchillas is described along with medical conditions common in this age group. Clinical signs of pain, safe analgesics, therapeutics, and alternative modalities are outlined along with guidelines for end-of-life care and decision-making. A handout containing advice for small mammal herbivore clients with geriatric pets is included.

Companion animals as a potential source of Giardia intestinalis infection in humans in the Czech Republic - A pilot study

Giardia intestinalis is a common enteric single-celled parasite infecting both humans and animals. Its eight morphologically identical but genetically distinct groups called assemblages differ from each other in host range. While assemblages A and B infect a wide range of hosts, including humans, the other assemblages (C to H) limit their host preferences to particular animal groups only. In companion animals as Giardia hosts, genotyping data have previously shown various results depending on pet species, location, environmental or breeding conditions, and the study design. To strengthen available epidemiological data from developed countries and to evaluate the role of pets in Giardia zoonotic transmission, we investigated Giardia-positive stool samples of three pet species (54 dogs, 18 cats, and 18 chinchillas) by a sequence-based analysis of three Giardia genes (β-giardin, glutamate dehydrogenase and triose phosphate isomerase). In dog samples, we confirmed assemblage C (21/54), assemblage D (32/54), and one case of a mixed infection C + D (1/54). In cats, we found assemblage F (16/18) and assemblage A, specifically sub-assemblage AI (2/18). All Giardia samples from chinchillas were characterised as assemblage B, specifically sub-assemblage BIV (18/18). These results indicate that in the Czech Republic, pet dogs may not represent a source of Giardia infection for humans because of the presence of only canid-specific genotypes C and D. In contrast, other pets, namely, chinchillas and, to a lesser extent, cats, may pose a potential risk of Giardia transmission to owners or breeders because they can host zoonotic Giardia genotypes.

Oviduct morphology and estrogen receptors ERα and ERβ expression in captive Chinchilla lanigera (Hystricomorpha: Chinchillidae)

Chinchilla lanigera is a hystricomorph rodent from South America whose reproductive biology presents particular characteristics that distinguishes it from other Rodentia species, such as low reproductive rate, seasonal breeding pattern, and long estrous cycle. Nevertheless, reproductive features in female chinchillas are still poorly investigated, with a scarce knowledge concerning the estrous cycle and the histology of reproductive organs. In this study, we investigate the morphology, histomorphometry, secretory activity, and immunolocalization of estrogen receptors ERα and ERβ in oviducts of nulliparous chinchillas, euthanized at fall season in Brazil. Follicular phase of estrous cycle of all studied animals was characterized by ovary and uterine morphology inspection, as well as vaginal cytology. Similar to other mammals, the oviduct wall of infundibulum, ampulla and isthmus was composed of mucosa, muscle, and serosa layers. Morphometric data of oviduct layers were used for identifying each oviduct segment. In the follicular phase, the oviduct was characterized by intense secretory activity, mainly in the ampulla, and expression of ERα and ERβ throughout the oviduct epithelium. Both ERα and ERβ were also detected in the connective tissue and smooth muscle cells. Our findings point out to the important role of estrogen in this female organ. Similar wide distribution of both ER proteins has been described for human Fallopian tube. Taken together, our data add to the understanding of the reproductive biology of female chinchillas, and may assist in the intensive breeding of this species and any eventual endeavor for conservation of chinchillas in the wild.

Mandible strength and geometry in relation to bite force: a study in three caviomorph rodents

The monophyletic group Caviomorpha constitutes the most diverse rodent clade in terms of locomotion, ecology and diet. Caviomorph species show considerable variation in cranio-mandibular morphology that has been linked to the differences in toughness of dietary items and other behaviors, such as chisel-tooth digging. This work assesses the structural strength of the mandible of three caviomorph species that show remarkable differences in ecology, behavior and bite force: Chinchilla lanigera (a surface-dwelling species), Octodon degus (a semi-fossorial species) and Ctenomys talarum (a subterranean species). Finite element (FE) models of the mandibles are used to predict the stresses they withstand during incisor biting; the results are related to in vivo bite forces and interspecific variations in the mandibular geometries. The study concludes that the mandible of C. talarum is better able to withstand strong incisor bites. Its powerful adducting musculature is consistent with the notorious lateral expansion of the angular process and the masseteric crest, and the enhanced cortical bone thickness. Although it has a relatively low bite force, the mandible of O. degus also shows a good performance for mid-to-strong incisor biting, in contrast to that of C. lanigera, which exhibits, from a mechanical point of view, the worst performance. The mandibles of C. talarum and O. degus appear to be better suited to withstand stronger reaction forces from incisor biting, which is consistent with their closer phylogenetic affinity and shared digging behaviors. The contrast between the low in vivo bite force of C. lanigera and the relatively high estimations that result from the models suggests that its adductor musculature could play significant roles in functions other than incisor biting.

Comparison of the characteristics of chinchilla epidydimal semen after collection, storage at 5°C and cryopreservation

The aim of the study was to compare the characteristics of chinchilla epididymal sperm: fresh, stored at liquid state and cryopreserved. Epididymal spermatozoa obtained from 11 males were assessed for subjective motility, concentration, motility parameters measured by CASA, viability, morphology, membrane integrity, acrosome integrity, mitochondrial potential, lipid peroxidation, chromatin structure, apoptotic changes and capacitation. Then half of the spermatozoa were stored at 5°C for 30 hr, and the second half was cryopreserved. After storage and thawing the same parameters as in fresh semen were assessed. Fresh semen showed good quality, with low levels of lipid peroxidation, chromatin fragmentation and capacitation. CASA evaluation showed significantly lower values for MOT, PMOT, RAPID, VCL, VAP and VSL after both storage at liquid state and cryopreservation (p < 0.05). Cold storage did not induce membrane and acrosome damage (p > 0.05), conversely to cryopreservation (p < 0.05). After storage, there was a drop in high mitochondrial potential in live cells (p < 0.05) and an increase in the percentage of non-apoptotic, capacitated cells (p < 0.05). These changes were not seen after cryopreservation (p > 0.05). Lipid peroxidation in live cells and chromatin structure remained unchanged both after storage and cryopreservation (p > 0.05). The study showed that examined methods of semen preservation exerted different patterns of changes in spermatozoa and that sperm quality after both of them allowed for further use of preserved spermatozoa in artificial reproductive techniques.

A natural zoonotic giardiasis: Infection of a child via Giardia cysts in pet chinchilla droppings

Here, we report a case of direct zoonotic transmission of giardiasis between a pet chinchilla and a human. Microscopic and molecular examinations of stool samples from a child and samples of chinchilla droppings revealed cysts/DNA of Giardia intestinalis. The transmission from the chinchilla to the child has been confirmed as coprophagous after the 1-year-old toddler ingested pet chinchilla droppings. Molecular analysis of the gdh gene from both hosts classified the G. intestinalis cysts into the assemblage B genetic group, which has been previously shown to be characteristic of both human and chinchilla giardiasis. Both Giardia sub-assemblages BIII and BIV were present in the chinchilla droppings, whereas only the sub-assemblage BIV was isolated from the child's stool sample. To the best of our knowledge, this is the first report of a true zoonotic transmission of giardiasis, supporting the zoonotic potential of assemblage B.

Safety of transtympanic application of probiotics in a chinchilla animal model

Background

Chronic suppurative otitis media can be recalcitrant and difficult to treat, particularly with the increasing occurrence of antibiotic resistance. Lactobacillus plantarum is a probiotic that has been shown to decrease S. aureus and P. aeruginosa growth in wounds, making it a good candidate for the treatment of chronic suppurative otitis media. However, before it can be applied in the ear, its ototoxicity potential must be evaluated.

Methods

A prospective controlled trial was conducted in a chinchilla animal model at the Animal care research facilities of the Montreal Children’s Hospital Research Institute to determine whether Lactobacillus plantarum is ototoxic when applied transtympanically. Ten chinchillas each had one ear randomly assigned to receive 10⁹ CFU/mL of Lactobacillus plantarum solution, while the contralateral ear received saline. Auditory brainstem responses were measured bilaterally at 8, 20, 25 kHz before, at 7–10 days after application, and at 28 days after application of probiotic or saline. Facial nerve and vestibular function were assessed clinically.

Results

There were no statistically significant differences in hearing thresholds between control and experimental ears at 28 days after application. A difference of 11 dB was noted in the 25 kHz range at day 7–10, but resolved by day 28. No animals receiving probiotics developed vestibular nerve dysfunction. There was no histologic evidence of auditory hair cell damaged evidenced by scanning electron microscopy.

Conclusion

Our study suggests that a single application of Lactobacillus plantarum at 10⁹ CFU/mL does not cause ototoxicity in a chinchilla animal model. These preliminary safety evaluations and the pathogen inhibitory effects of L. plantarum demonstrated by previous studies present this probiotic as a candidate of interest for further investigation.

Electronic supplementary material

The online version of this article (10.1186/s40463-017-0242-y) contains supplementary material, which is available to authorized users.

"On-command" dissolvable tympanostomy tube in the chinchilla model: A proof of concept

OBJECTIVES

To prove the concept that a dissolvable "on-command" tympanostomy tube placed into the tympanic membrane of a chinchilla can dissolve when a benign solution is applied and result in a well healed tympanic membrane without histologic evidence of injury.

STUDY DESIGN

Prospective Randomized Single-Subject Controlled Trial.

METHODS

Prototype tympanostomy tubes were fabricated from poly(butyl methacrylate-co-(2-dimethylaminoethyl) methacrylate-co- methyl methacrylate) (PBM). "In vitro" dissolution studies were performed with applications of the benign chemical, hydrogen peroxide (HP). PBM tubes were placed into ten chinchilla tympanic membranes matched with standard plastic tubes placed into the contralateral side. All 20 tubes were exposed to HP for 21 days with serial endoscopic examinations. In vitro PBM tubes were weighed before and after interventions and compared to control tubes. In vivo photo documentation was used to show progression of dissolution and histologic slides were obtained to show the effect of the PBM on surrounding tissues.

RESULTS

Compared to control tubes, all those exposed to hydrogen peroxide had a statistically significant reduction in weight (p < 0.01). After placement into the tympanic membrane of chinchillas, all PBM tubes dissolved within 21 days of hydrogen peroxide treatment leaving behind histologically normal, intact tympanic membranes.

CONCLUSION

Our PBM tubes dissolve "on-command" in a chinchilla model when exposed to treatment with a benign chemical. Dissolvable "on-command" tympanostomy tubes may reduce significant complications related to pediatric tympanostomy tube use.

Can floseal™ be applied safely during otologic surgery? Assessment of ototoxicity in a chinchilla animal model

Background

In otologic surgery good visualization is paramount, and patients with bleeding diatheses or who need to be anti-coagulated can present a significant challenge. Here, we determine whether Floseal™, a hemostatic matrix, is ototoxic in a validated animal model.

Methods

Nine chinchillas housed in the animal care facilities of the Montreal Children’s Hospital Research Institute were used for the study. After a myringotomy incision was made in each tympanic membrane, baseline auditory brainstem response measurements were performed at 8, 20, and 25 kHz. In each animal one ear was randomized to receive Floseal™ to the middle ear cavity, whereas the other ear served as the control and received 0.9% sodium chloride. Outcome measures included early (day 7) and late (day 30) auditory brainstem response, clinical evidence of facial nerve or vestibular disturbance and histological evidence of ototoxity.

Results

There was no significant hearing threshold shift on auditory brainstem response across all tested frequencies for both experimental and control ear. No animals receiving Floseal™ developed facial or vestibular nerve dysfunction and there was no histological evidence of ototoxicity.

Conclusion

Based on the preliminary ototoxicity assessment on nine chinchillas, transtympanic Floseal™ does not appear to be ototoxic. More studies are warranted to assess the safety and applicability of the product in humans.

Dynamic property changes in stapedial annular ligament associated with acute otitis media in the chinchilla

Located at the end of the ossicular chain, the stapedial annular ligament (SAL) serves as a closed yet mobile boundary between the cochlear fluid and stapes footplate. It is unclear how SAL properties change with acute otitis media (AOM). This paper reports the measurements of SAL dynamic properties in chinchilla AOM model using dynamic mechanical analyzer (DMA) and frequency-temperature superposition (FTS) principle. AOM was analyzed in two infection groups: 4 days (4D) and 8 days (8D) post induction. SAL specimens were measured using DMA at three temperatures: 5, 25, and 37°C. To extend the testing frequencies to higher levels, FTS principle was employed. Then generalized Maxwell model was utilized to define the constitutive equations of the SAL. The complex shear moduli were obtained from seven samples of control, 4D, and 8D groups. Results show that the storage and loss shear moduli of SALs decreased due to AOM. The storage moduli for 4D and 8D ears were similar below 100Hz, and the loss modulus for 4D was significantly larger than 8D across the entire frequency range. This study reports data that contributes to ear biomechanics and improves understanding on the effects of AOM in middle ear tissues.

Morphological changes in the round window membrane associated with Haemophilus influenzae-induced acute otitis media in the chinchilla

OBJECTIVE

The round window membrane (RWM) encloses the round window, the opening into the scala tympani (ST) from the middle ear. During the course of acute otitis media (AOM), structural changes of the RWM can occur that potentially affect sound transmission into and out of the cochlea. The relationship between such structural changes and conductive hearing loss during AOM has remained unclear. The focus of the current study was to compare the thickness distribution across the RWM surface between normal ears and those with AOM in the chinchilla. We assessed the occurrence of AOM-associated histological changes in this membrane compared to uninfected control animals after AOM of two relatively short durations.

MATERIAL AND METHODS

AOM was induced by transbullar injection of the nontypeable Haemophilus influenzae strain 86-028NP into two groups of adult chinchillas (n = 3 each). Bullae were obtained from the two infected groups, at 4 days or 8 days post challenge. Structures and thickness of these RWMs were compared between the two infected treatment groups and to RWMs from uninfected control animals (n = 3) at seven different RWM locations.

RESULTS

RWM thickness in infected chinchillas increased significantly at locations along the central line on the 4th day post bacterial challenge compared to values found for uninfected control animals. Lymphocyte infiltration and edema were the primary contributors to these thickness increases. No significant further increases in RWM thickness were observed when RWMs from chinchillas ears infected for 4 and 8 days were compared. Thickness and structural changes at the RWM lateral and medial areas were less visually obvious and not statistically significant among the three treatment groups. These latter RWM regions clearly were less affected during AOM than the central areas.

CONCLUSIONS

This histological study establishes that H. influenzae-induced AOM causes significant acute changes in chinchilla RWM structure that are characterized by region-specific increases in thickness. Our new morphological findings comparing normal and diseased chinchilla RWMs identify yet another biomechanical mechanism by which nontypeable H. influenzae may contribute to hearing loss in AOM.

Characterization of the nonlinear elastic behavior of chinchilla tympanic membrane using micro-fringe projection

The mechanical properties of an intact, full tympanic membrane (TM) inside the bulla of a fresh chinchilla were measured under quasi-static pressure from -1.0 kPa to 1.0 kPa applied on the TM lateral side. Images of the fringes projected onto the TM were acquired by a digital camera connected to a surgical microscope and analyzed using a phase-shift method to reconstruct the surface topography. The relationship between the applied pressure and the resulting volume displacement was determined and analyzed using a finite element model implementing a hyperelastic 2(nd)-order Ogden model. Through an inverse method, the best-fit model parameters for the TM were determined to allow the simulation results to agree with the experimental data. The nonlinear stress-strain relationship for the TM of a chinchilla was determined up to an equibiaxial tensile strain of 31% experienced by the TM in the experiments. The average Young's modulus of the chinchilla TM from ten bullas was determined as approximately 19 MPa.

Middle-ear and inner-ear contribution to bone conduction in chinchilla: The development of Carhart's notch

While the cochlea is considered the primary site of the auditory response to bone conduction (BC) stimulation, the paths by which vibratory energy applied to the skull (or other structures) reaches the inner ear are a matter of continued investigation. We present acoustical measurements of sound in the inner ear that separate out the components of BC stimulation that excite the inner ear via ossicular motion (compression of the walls of the ear canal or ossicular inertia) from the components that act directly on the cochlea (cochlear compression or inertia, and extra-cochlear 'third-window' pathways). The results are consistent with our earlier suggestion that the inner-ear mechanisms play a large role in bone-conduction stimulation in the chinchilla at all frequencies. However, the data also suggest the pathways that conduct vibration to the inner ear via ossicular-motion make a significant contribution to the response to BC stimulation in the 1-3 kHz range, such that interruption of these path leads to a 5 dB reduction in total stimulation in that frequency range. The mid-frequency reduction produced by ossicular manipulations is similar to the 'Carhart's notch' phenomenon observed in otology and audiology clinics in cases of human ossicular disorders. We also present data consistent with much of the ossicular-conducted sound in chinchilla depending on occlusion of the ear canal.

Suppression Measured from Chinchilla Auditory-Nerve-Fiber Responses Following Noise-Induced Hearing Loss: Adaptive-Tracking and Systems-Identification Approaches

The compressive nonlinearity of cochlear signal transduction, reflecting outer-hair-cell function, manifests as suppressive spectral interactions; e.g., two-tone suppression. Moreover, for broadband sounds, there are multiple interactions between frequency components. These frequency-dependent nonlinearities are important for neural coding of complex sounds, such as speech. Acoustic-trauma-induced outer-hair-cell damage is associated with loss of nonlinearity, which auditory prostheses attempt to restore with, e.g., "multi-channel dynamic compression" algorithms.Neurophysiological data on suppression in hearing-impaired (HI) mammals are limited. We present data on firing-rate suppression measured in auditory-nerve-fiber responses in a chinchilla model of noise-induced hearing loss, and in normal-hearing (NH) controls at equal sensation level. Hearing-impaired (HI) animals had elevated single-fiber excitatory thresholds (by ~ 20-40 dB), broadened frequency tuning, and reduced-magnitude distortion-product otoacoustic emissions; consistent with mixed inner- and outer-hair-cell pathology. We characterized suppression using two approaches: adaptive tracking of two-tone-suppression threshold (62 NH, and 35 HI fibers), and Wiener-kernel analyses of responses to broadband noise (91 NH, and 148 HI fibers). Suppression-threshold tuning curves showed sensitive low-side suppression for NH and HI animals. High-side suppression thresholds were elevated in HI animals, to the same extent as excitatory thresholds. We factored second-order Wiener-kernels into excitatory and suppressive sub-kernels to quantify the relative strength of suppression. We found a small decrease in suppression in HI fibers, which correlated with broadened tuning. These data will help guide novel amplification strategies, particularly for complex listening situations (e.g., speech in noise), in which current hearing aids struggle to restore intelligibility.

Assessment of ototoxicity of tea tree oil in a chinchilla animal model

OBJECTIVE

The aim of the present study is to examine the effects of tea tree oil on hearing function and cochlear morphology after intratympanic administration in a chinchilla animal model.

METHODS

Nine chinchillas received intratympanic injection of 3% tea tree oil dissolved in olive oil in one ear, whereas the contralateral control ear received olive oil only. Outcome measures included auditory brainstem responses conducted before treatment and at 10 days and 30 days following the injection. Post-mortem cochlear morphology was assessed using scanning electron microscopy.

RESULTS

At 10 and 30 days following the injection, there was no significant change in auditory brain response thresholds at 8, 16, 20 or 25kHz. Scanning electron microscopy imaging showed no damage to auditory hair cells.

CONCLUSION

Tea tree oil (3%) does not appear to be ototoxic in a chinchilla animal model. Future preclinical and clinical studies are required to establish the effectiveness of TTO in treating otitis.

Rodent nutrition: digestive comparisons of 4 common rodent species

This article summarizes the literature regarding digestive strategies and captive diets of common rodent pocket pets. A comparison is made between the 2 suborders in which chinchillas, guinea pigs, hamsters, and gerbils occur, highlighting digestive anatomy and dietary adaptations. Recommended captive diets are provided, as well as common nutritionally related health issues that may be presented to veterinary clinics.

Pneumococcal PspA and PspC proteins: potential vaccine candidates for experimental otitis media

OBJECTIVE

Otitis media is the most commonly diagnosed disease in ambulatory care and Streptococcuspneumoniae continues to be the most common bacterial agent. Bacterial resistance to antibiotics underscores the need for better vaccines. Current pneumococcal conjugate vaccines are modestly protective against otitis media; however, limited serotype coverage and serotype replacement have led to the investigation of pneumococcal proteins as potential vaccine candidates. Two proteins, pneumococcal surface proteins A (PspA) and C (PspC) are important virulence factors, expressed by virtually all strains. Although a number of pneumococcal proteins have been investigated in other infection sites, these proteins can have diverse organ-specific effects. In this study, we investigated the viability and virulence of single (PspA(-) and PspC(-)) and double (PspA(-)/PspC(-)) mutants of pneumococcal PspA and PspC proteins in the chinchilla middle ear.

METHODS

Bullae of 24 chinchillas were inoculated with 0.5 ml of 10(6) colony forming units (CFUs)/ml bacteria: 6 with wild-type D39 strain; 6 with PspA(-); 6 with PspC(-); and 6 with PspA(-)/PspC(-) isogenic mutant strains. Bacterial CFU levels in middle ear effusions and light microscopic analysis of the number of inflammatory cells in the round window membrane (RWM) were compared 48 h after inoculation.

RESULTS

At 48 h, CFUs in middle ears were increased for wild-type and PspC(-) strains compared to inoculum levels; however, they were significantly less for the group inoculated with the PspC(-) strain compared to wild-type strain. No bacteria were detected in the PspA(-) and PspA(-)/PspC(-) groups. The number of inflammatory cells in the RWM was significantly higher in wild-type compared to the PspA(-), PspC(-), and PspA(-)/PspC(-) groups. No significant difference in number of inflammatory cells was observed between any pairs of groups inoculated with mutant strains.

CONCLUSION

Viability and virulence of the PspC(-) strain were similar to the wild-type strain. The single PspA(-) and double PspA(-)/PspC(-) mutants were highly attenuated in the ear. Bacterial clearance of the PspA(-)/PspC(-) double mutant was indistinguishable from that of the PspA mutant. These studies provide no reason to exclude PspC from a multi-component protein vaccine containing PspA.

Pathology of the exotic companion mammal gastrointestinal system

A variety of disease agents can affect the gastrointestinal tract of the exotic companion mammal, some of which can pose zoonotic health concerns. Many conditions present with nonspecific clinical signs (lethargy, variable degrees of diarrhea, and for most sick rodents, presenting hunched with spiky fur), necessitating additional laboratory testing to reach a diagnosis. Primary tumors of the digestive tract are also presented as well as miscellaneous conditions ranging from toxins to trauma.

Earigate™ for softening ear wax: is it safe when the eardrum is perforated?

OBJECTIVE

To determine the safety of Earigate™ as an ear wax softening product.

STUDY DESIGN

Prospective, controlled animal study.

METHODS

Bilateral wide myringotomies were performed in eleven chinchillas. In each animal, Earigate™ was delivered to a randomly selected experimental ear canal as 2 puffs twice a day. Auditory brainstem response (ABR) was used to assess the hearing of the animals before, 3 days and 10 days following the local application of Earigate™. The ABR threshold shifts were compared for both experimental and control ears.

RESULTS

The mean hearing threshold shifts in the experimental animals were comparable at all frequencies and at days 3 and 10. No statistically significant differences were observed in the mean threshold shifts for all of the frequencies evaluated, between the control and experimental ears.

CONCLUSIONS

The administration of Earigate™ to the middle ear of chinchillas did not cause any ototoxicity as assessed by ABR.

Kinetic analysis and evaluation of the mechanisms involved in the resolution of experimental nontypeable Haemophilus influenzae-induced otitis media after transcutaneous immunization

Transcutaneous immunization (TCI) is a simple and needle-free method with which to induce protective immune responses. Using a chinchilla model of nontypeable Haemophilus influenzae (NTHI)-induced otitis media (OM), we examined the efficacy afforded by TCI with a novel chimeric immunogen called 'chimV4' which targets two critical adhesins expressed by NTHI, outer membrane protein P5 and the majority subunit of NTHI Type IV pilus, PilA. Experimental OM was first established in cohorts of animals, and then TCI performed via a therapeutic immunization regime by rubbing vaccine formulations on hydrated pinnae. The kinetics of resolution of established experimental disease was evaluated by clinically-relevant assessments of OM, bacterial culture of planktonic and adherent NTHI within the middle ear and gross examination of the relative amount of NTHI mucosal biofilms within the middle ear space. Within seven days after primary TCI, a significant reduction in the signs of OM, significantly fewer NTHI adherent to the middle ear mucosa and significant resolution of mucosal biofilms was detected in animals that received chimV4+ the adjuvant LT(R192G-L211A), compared to animals administered LT(R192G-L211A) alone or saline by TCI (p<0.05) with eradication of NTHI within an additional seven days. The mechanism for rapid disease resolution involved efflux of activated dermal dendritic cells from the pinnae after TCI, secretion of factors chemotactic for CD4(+) T-cells, induction of polyfunctional IFNγ- and IL-17-producing CD4(+) T-cells and secretion of host defense peptide within the middle ear. These data support TCI as a therapeutic intervention against experimental NTHI-induced OM and begin to elucidate the host response to immunization by this noninvasive regimen.