Fleas and bites in bones

BOYDE, A.; MILLS, D.; ABBA, A.M.; EZQUIAGA, M.C.

Cardiff

Encuentro; BONE RESEARCH SOCIETY and BRITISH ORTHOPAEDIC RESEARCH SOCIETY 5TH JOINT MEETING; 2019

BONE RESEARCH SOCIETY and BRITISH ORTHOPAEDIC RESEARCH SOCIETY

Armadillos are bitten by several species of flea. Females of the genus Tunga penetrate the epidermis and when in place are fertilised by males, after which the abdomen increases in size by up to ten times to form a ?neosome?. Within the penetrans group of Tunga, a new species, T. perforans, discovered by Ezquiaga et al (Medical and Veterinary Entomology 2015 29, 196?204) perforates the bones within the integument of its host. We hypothesised that the cavities eaten into the bone might be generated by recruitment of the host's osteoclasts and that they would resemble Howship's lacunae, being formed of multiples of small resorption pits.We studied bones from two species, Chaetophractus villosus [greater hairy armadillo] and Tolypeutes matacus [southern three-banded armadillo, a species capable of rolling into a complete ball in self- defence] which showed the characteristic 2 to 3 mm diameter 'flea bite' holes in the external surfaces of the osteoderms. For backscattered electron scanning electron microscopy [BSE SEM: Zeiss EVO-MA10] samples were studied after treatment with sodium hypochlorite bleach to remove residual adherent soft tissue and contaminant soil or dust particles, washed, dried and imaged uncoated at 20kV, 50Pa chamber pressure. For x-ray microtomography (XMT: QMUL MuCat2 system, 90kV), larger samples consisting of many adherent osteoderms were cut to isolate regions containing the bony lesions and imaged at 10 micron voxel resolution. 3D rendering was performed using Drishti software.3D BSE-SEM of the deepest lesions showed resorption pit complexes characteristic of those made by osteoclasts. Many lesions were centred on the syndesmoses between adjacent bones, but some on the centres of bones. Shallower lesions showed evident signs of repair by deposition of new bone. XMT showed extra non-bone space tunnels converging on the lesions, analogous to the micro-anatomy of overload arthrosis lesions in equine fetlock joints which we have studied extensively.We conclude that the Tunga neosome creates a local host response which causes bone resorption, creating the space in which it can grow. Owing to the superficial location of the lesions, we speculate whether this might constitute a useful experimental model in the future.