Fear of falling avoidance behavior affects the inter-relationship between vision impairment and diminished mobility in community-dwelling older adults.

BACKGROUND: Age-related decline in vision may contribute to the development of fear of falling (FOF) behavior and reduced mobility, which are related to increased fall risk in older adults. PURPOSE: To investigate the inter-relationship between vision impairment, physical mobility performance, and FOF behavior in community-dwelling older adults. METHODS: A total of 400 participants from community centers (267 females; age = 74.8 (6.4), range = 65-97 years) participated in this cross-sectional study. Presence of age-related eye diseases (e.g. macular degeneration, cataracts, glaucoma, and retinopathy) and visual acuity (VA) was assessed. Physical mobility and FOF avoidance behavior were assessed using the Timed Up-and-Go (TUG) test and the Fear of Falling Avoidance Behavior Questionnaire (FFABQ). The inter-relationships between parameters were analyzed using mediation model analysis. RESULTS: Significant decreases in mobility performance were observed in those with eye disease (eye disease = 9.56 [5.2] sec, no eye disease = 8.54 [2.75] sec; p = .037) and FOF avoidance behavior (avoiders = 12.87 [6.04] sec, non-avoiders = 8.51 [3.56] sec; p < .001). Furthermore, FOF behavior was found to significantly influence the inter-relationship between presence of eye disease and TUG performance (p = .004). VA alone had no significant effect on mobility (p = .69). CONCLUSION: The presence of eye disease and the associated FOF behavior was related to decreased mobility and potentially increased fall risk. We recommend clinicians to inquire about the presence of eye disease and FOF behavior to identify risk factors related to falls in older adults.

Disease dynamics of honeybees with Varroa destructor as parasite and virus vector.

The worldwide decline in honeybee colonies during the past 50 years has often been linked to the spread of the parasitic mite Varroa destructor and its interaction with certain honeybee viruses carried by Varroa mites. In this paper, we propose a honeybee-mite-virus model that incorporates (1) parasitic interactions between honeybees and the Varroa mites; (2) five virus transmission terms between honeybees and mites at different stages of Varroa mites: from honeybees to honeybees, from adult honeybees to the phoretic mites, from brood to the reproductive mites, from the reproductive mites to brood, and from adult honeybees to the phoretic mites; and (3) Allee effects in the honeybee population generated by its internal organization such as division of labor. We provide completed local and global analysis for the full system and its subsystems. Our analytical and numerical results allow us have a better understanding of the synergistic effects of parasitism and virus infections on honeybee population dynamics and its persistence. Interesting findings from our work include: (a) due to Allee effects experienced by the honeybee population, initial conditions are essential for the survival of the colony. (b) Low adult honeybees to brood ratios have destabilizing effects on the system which generate fluctuating dynamics that lead to a catastrophic event where both honeybees and mites suddenly become extinct. This catastrophic event could be potentially linked to Colony Collapse Disorder (CCD) of honeybee colonies. (c) Virus infections may have stabilizing effects on the system, and parasitic mites could make disease more persistent. Our model illustrates how the synergy between the parasitic mites and virus infections consequently generates rich dynamics including multiple attractors where all species can coexist or go extinct depending on initial conditions. Our findings may provide important insights on honeybee viruses and parasites and how to best control them.