Evergrowing incisors of diprotodont marsupials record age and life history.

OBJECTIVE: Tooth growth and wear are commonly used tools for determining the age of mammals. The most speciose order of marsupials, Diprotodontia, is characterised by a pair of procumbent incisors within the lower jaw. This study examines the growth and wear of these incisors to understand their relationship with age and sex. DESIGN: Measurements of mandibular incisor crown and root length were made for two sister species of macropodid (kangaroos and wallabies); Macropus giganteus and Macropus fuliginosus. Histological analysis examined patterns of dentine and cementum deposition within these teeth. Broader generalisability within Diprotodontia was tested using dentally reduced Tarsipes rostratus - a species disparate in body size and incisor function to the studied macropodids. RESULTS: In the macropodid sample it is demonstrated that the hypsodont nature of these incisors makes measurements of their growth (root length) and wear (crown length) accurate indicators of age and sex. Model fitting finds that root growth proceeds according to a logarithmic function across the lifespan, while crown wear follows a pattern of exponential reduction for both macropodid species. Histological results find that secondary dentine deposition and cementum layering are further indicators of age. Incisor measurements are shown to correlate with age in the sample of T. rostratus. CONCLUSIONS: The diprotodontian incisor is a useful tool for examining chronological age and sex, both morphologically and microstructurally. This finding has implications for population ecology, palaeontology and marsupial evolution.

Addressing the mental health needs of children affected by HIV in Rwanda: validation of a rapid depression screening tool for children 7-14 years old.

BACKGROUND: Depression in children presents a significant health burden to society and often co-exists with chronic illnesses, such as human immunodeficiency virus (HIV). Research has demonstrated that 10-37% of children and adolescents living with HIV also suffer from depression. Low-and-middle income countries (LMICs) shoulder a disproportionate burden of HIV among other health challenges, but reliable estimates of co-morbid depression are lacking in these settings. Prior studies in Rwanda, a LMIC of 12 million people in East Africa, found that 25% of children living with HIV met criteria for depression. Though depression may negatively affect adherence to HIV treatment among children and adolescents, most LMICs fail to routinely screen children for mental health problems due to a shortage of trained health care providers. While some screening tools exist, they can be costly to implement in resource-constrained settings and are often lacking a contextual appropriateness. METHODS: Relying on international guidelines for diagnosing depression, Rwandan health experts developed a freely available, open-access Child Depression Screening Tool (CDST). To validate this tool in Rwanda, a sample of 296 children with a known diagnosis of HIV between ages 7-14 years were recruited as study participants. In addition to completing the CDST, all participants were evaluated by a mental health professional using a structured clinical interview. The validity of the CDST was assessed in terms of sensitivity, specificity, and a receiver operating characteristic (ROC) curve. RESULTS: This analysis found that depression continues to be a co-morbid condition among children living with HIV in Rwanda. For identifying these at-risk children, the CDST had a sensitivity of 88.1% and specificity of 96.5% in identifying risk for depression among children living with HIV at a cutoff score of 6 points. This corresponded with an area under the ROC curve of 92.3%. CONCLUSIONS: This study provides evidence that the CDST is a valid tool for screening depression among children affected by HIV in a resource-constrained setting. As an open-access and freely available tool in LMICs, the CDST can allow any health practitioner to identify children at risk of depression and refer them in a timely manner to more specialized mental health services. Future work can show if and how this tool has the potential to be useful in screening depression in children suffering from other chronic illnesses.