Ecological Archives E091-021-A2

Daniel J. Salkeld and Robert S. Lane. 2010. Community ecology and disease risk: lizards, squirrels, and the Lyme disease spirochete in California, USA. Ecology 91:293–298.

Appendix B. Results of sensitivity tests on the parameters used for the "host-community" model.

Sensitivity analyses demonstrated that squirrels and lizards played the predominant roles in determining disease risk. Because small mammals were not infected with B. burgdorferi, adjusting the abundance parameters for each host species had no impact upon nymphal infection prevalence (Fig. B1). However, increasing squirrel abundance by 20% increased nymphal infection prevalence, and increasing lizard abundance, especially western fence lizards, which have higher larval tick loads than alligator lizards, reduced disease risk.

Similarly, increasing infestations of Ixodes pacificus larvae only affected disease risk when applied to squirrel and lizard tick loads (Fig B1).

The largest impact of altering the model's parameters occurred when the host's infection prevalence was modified. This may be the most pertinent model alteration because PCR analysis of ear-punch biopsies may fail to detect B. burgdorferi even if the animal is infected (Salkeld et al. 2008). In this scenario, nymphal infection prevalence increased in all cases where mammalian infection prevalence is applicable (lizard parameters remained unaltered because immune factors destroy the spirochete (Lane and Quistad 1998, Wright et al. 1998, Kuo et al. 2000). Nonetheless, disease risk responded most obviously to increases in infection prevalence for the population of western gray squirrels.

 
   FIG. B1. The impact upon nymphal infection prevalence of 20% increases in host abundance (top), larval loads (middle), and prevalence of infection (bottom) for each vertebrate species, calculated by the host community model. (Host species: mica = Microtus californicus, pebo = Peromyscus boylii, petr = P. truei, pema = P. maniculatus, nefu = Neotoma fuscipes, scgr = Sciurus griseus, elca = Elgaria multicarinata, scoc = Sceloporus occidentalis).

LITERATURE CITED

Kuo, M. M., R. S. Lane, and P. C. Giclas. 2000. A comparative study of mammalian and reptilian alternative pathway of complement-mediated killing of the Lyme disease spirochete (Borrelia burgdorferi). Journal of Parasitology 86:1223–1228.

Lane, R. S., and G. B. Quistad. 1998. Borreliacidal factor in the blood of the western fence lizard (Sceloporus occidentalis). Journal of Parasitology 84:29–34.

Salkeld, D. J., S. Leonhard, Y. A. Girard, N. Hahn, J. Mun, K. A. Padgett, and R. S. Lane. 2008. Identifying the reservoir hosts of the Lyme disease spirochete Borrelia burgdorferi in California: the role of the western gray squirrel (Sciurus griseus). American Journal of Tropical Medicine and Hygiene 79:535–540.

Salkeld, D. J., S. Leonhard, Y. A. Girard, N. Hahn, J. Mun, K. A. Padgett, and R. S. Lane. 2008. Identifying the reservoir hosts of the Lyme disease spirochete Borrelia burgdorferi in California: the role of the western gray squirrel (Sciurus griseus). American Journal of Tropical Medicine and Hygiene 79:535–540.

Wright, S. A., R. S. Lane, and J. R. Clover. 1998 Infestation of the southern alligator lizard (Squamata: Anguidae) by Ixodes pacificus (Acari: Ixodidae) and its susceptibility to Borrelia burgdorferi. Journal of Medical Entomology 35:1044–1049.


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