Resistance of cotton rats, Sigmodon hispidus, to primary infection by Nippostrongylus brasiliensis

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., Hymenolepisdiminuta, 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.

Analysis of antibody response by temperature-sensitive measles vaccine strain in the cotton rat model

Measles virus (MeV) vaccine strain, AIK-C, is temperature sensitive (ts), which is thought to be associated with attenuation of virus pathogenicity. In this study, replication and antibody response were examined in cotton rats using viruses carrying different forms of the P gene, which is responsible for the ts phenotype of strain AIK-C and its parental Edmonston strain. When cotton rats were inoculated intranasally, ts viruses neither replicated in lungs, nor reproducibly generated an antibody response. When inoculated intramusculary (i.m.), however, ts strains raised an antibody titer in all animals. This response was not observed when ultraviolet-inactivated virus was used. ts virus, inoculated i.m., was recovered from cotton rat drainage lymph nodes. These results suggest that ts virus, inoculated i.m., could replicate in the cotton rat, presumably at the superficial lymph node, and induce an antibody response. Therefore, cotton rats can serve as a small-animal model for investigating immune responses to safer ts vaccine, as well as recombinant vaccine using AIK-C as a vector for protection against other infectious agents.

Enhanced protection against the migratory phase, but defective protection against the intestinal phase of Strongyloides venezuelensis infection in cotton rats, Sigmodon hispidus

The protective capacity of the cotton rat, Sigmodon hispidus, against the migratory and intestinal phases of Strongyloides venezuelensis infection was examined. After subcutaneous infection with infective larvae (L(3)), adult worm recovery rates from male and female animals on Day 71 were only 0.10% and 0.06% of initial dose, respectively. To determine whether this enhanced protection was expressed during the migratory phase or the intestinal phase, larval recovery from the lungs of cotton rat was evaluated 3 days after subcutaneous L(3) infection. The larval recovery rate was only 0.5% of initial dose and about 40-fold lower than that from control mice. Protection in the intestine was also evaluated after intraduodenal implantation of adult worms. About 30% of implanted worms became established and worm burden remained constant until Day 28. Despite a high worm burden on Day 28, EPG was about 25-fold lower than the peak count. To evaluate expulsive capacity and monitor the cellular responses in the intestine of cotton rats, adult Nippostrongylus brasiliensis worms were implanted in addition to S. venezuelensis. Cotton rats were unable to expel adult S. venezuelensis worms, even after 21 days of observation. Although the number of mucosal mast cells increased significantly, the intraepithelial migration of mast cells was not observed. In contrast, N. brasiliensis was expelled by Day 6 in association with goblet cell hyperplasia. These results suggest that in cotton rats, the defective intestinal protection against adult S. venezuelensis worms results from dysfunction of mucosal mast cells.