Prevalence of Dirofilaria immitis and Dipetalonema reconditum infections in Missouri dogs. 
The prevalence of Dirofilaria immitis and Dipetalonema reconditum infections in Missouri dogs was investigated by means of a statewide veterinary mail survey and a study of shelter dogs from central Missouri and Mississippi River communities.  The veterinary survey revealed microfilariae of D immitis in 447 of 11,823 (3.8%) dogs, microfilariae of D reconditum in 14 (0.1%), and microfilariae of both species in 8 (less than 0.1%).  Of 493 shelter dogs examined, using the modified Knott test, 23 (4.7%) were positive for D immitis, 23 (4.7%) for D reconditum, and 2 (0.4%) for both helminths.  The prevalence of infection with both D immitis (9.4%) and D reconditum (6.3%) was higher in shelter dogs from the Mississippi River communities than in those from central Missouri (1.7% for D immitis, 3.7% for D reconditum).  The microfilariae of D immitis in shelter dogs ranged in length from 255 to 343 micrometer (mean, 314 micrometer) and in width from 5.0 to 7.5 micrometer (mean, 6.5 micrometer); those of D reconditum ranged in length from 238 to 295 micrometer (mean, 257 micrometer) and in width from 3.2 to 6.5 micrometer (mean, 4.9 micrometer).  Buttonhook tails were seen in 41% of D reconditum.  In the final analysis, the shape of the anterior end was considered the most reliable criterion for differentiation.