Incidence Modeling and Protocol for the Detection of Dirofilaria immitis in Montana

Abstract

Heartworm, Dirofilaria immitis, is a parasite that infects dogs (Thanchomnang et al., 2010), coyotes (Sacks et al., 2002), cats (Liu et al., 2005), and humans (Oleaga et al., 2009). D. immitus is transmitted from dog to dog through numerous mosquito vectors. Studies in Minnesota demonstrated the likelihood of Ae. vexans being the chief vector based on its frequent feeding habits and anatomy that are conducive for larvae growth (Bemrick & Sandholm, 1966). Therefore due to climate and geographical similarities, the most likely vector is Ae. vexans in Montana. Due to the climate dependent growth of D. immitis (American Heartworm Society 2007), mosquitoes from the summers of 2007 and 2005 were sampled (http://www.ncdc.noaa.gov/climate-monitoring/, accessed on 2/16/2011). These mosquitoes were examined using a SYBR-Green real time PCR assay since the SYBR-Green flourophore requires less specialization of the real time machine and allows for broader use of the method. The results from the real time PCR assay were compared with other factors that contribute to prevalence in the reservoir, such as: host population dynamics, transmission mechanism, environmental influences, and agricultural practices (Lloyd-Smith et al., 2009; Vezzani & Carbajo, 2006). The Vezzani & Carbajo (2006) factors were applied to Montana in predicting the risk zones. The development of the DNA extraction and SYBR-Green PCR protocol was successful and the results of the mosquito samples show that D. immitis is nonexistent or at least extremely rare within the mosquito populations in the Montana counties sampled. The risk assessment map strengthened the negative results from the real time PCR detection assay.