Infection of Mammary Glands of Small Mammals in Eastern North America by Helminths

SIMPLE SUMMARY: For several decades, it has been known that many species of parasitic worms can infect the mammary glands of their hosts, and that some of these can be transmitted through the mammary glands from mother to nursing young. Such infections have been studied widely in many species of wild and domesticated animals, including livestock as well as cats and dogs, and also in humans. Despite this, field studies specifically designed to determine whether mammary infections occur in wild mammals sampled from their natural environment have not been performed. We explored this by conducting a survey of wild small mammals from natural sites in the states of New York, Tennessee, and Georgia in the eastern United States. We examined 53 wild hosts, including four species of rodents and one shrew, using a new method of removing and mounting whole mammary glands for microscopical study. Many intestinal parasites were found, but worms occurred in the mammary glands of only one species; four cotton rats from Georgia had roundworm larvae in their mammary glands. This is the first general survey of wild mammals to include mammary examination. Based on our positive results, we propose inclusion of mammary examination in all future surveys. ABSTRACT: To determine whether small mammals living in natural settings harbor helminth infections in their mammary glands, we conducted a survey of helminths infecting rodents and soricimorphs in three widespread locations in the eastern United States: states of New York, Tennessee, and Georgia. We examined all the primary organs in all hosts, and identified all helminths. We also excised the complete mammary glands within their subcutaneous fat pads, then stained and mounted each whole mammary gland set for microscopical examination. A total of 53 individual hosts were examined, including 32 Peromyscus spp., 11 Mus musculus, 5 Sigmodon hispidus, 4 Clethrionomys gapperi, and 1 Blarina carolinensis. Helminths collected included Heligmosomoides sp., Hymenolepis diminuta, Hymenolepis nana, Pterygodermatites peromysci, Schistosomatium douthitti, Syphacia obvelata, Syphacia sigmodontis, and Trichostrongylus sigmodontis. Four S. hispidus were infected by T. sigmodontis in the small intestine; in all four, we also found nematode larvae in lactiferous duct lumen and lactogenic tissue of the mammary glands. We were unable to identify the species of nematode larvae, but the co-occurrence with T. sigmodontis in all cases may suggest an association. Future studies should seek to identify such larvae using molecular and other methods, and to determine the role of these mammary nematode larvae in the life cycle of the identified species. No other host species harbored helminths in the mammary glands. Overall, our results suggest that mammary infections in wild small mammals are not common, but warrant inclusion in future surveys.