library(PBSmapping); library(RgoogleMaps); library(maptools)
cases<-read.table("cases.csv")
cases.ppp<-ppp(cases@coords[,1], cases@coords[,2], unitname=c("km"))
dens.cas <- density.ppp(cases.ppp, bw)
plot(dens.cas)

shp <- importShapefile('map.shp', projection="LL");
bb <- qbbox(lat = shp[,"Y"], lon = shp[,"X"]);
MyMap <- GetMap.bbox(bb$lonR, bb$latR, destfile = "map.jpg");

PlotPolysOnStaticMap(MyMap, shp, lwd=.5, col = rgb(1,1,1,0.2), add = F)