Mycobacterium microti Tuberculosis in Its Maintenance Host, the Field Vole (Microtus agrestis)

Abstract

The field vole (Microtus agrestis) is a known maintenance host of Mycobacterium microti. Previous studies have shown that infected animals develop tuberculosis. However, the disease is also known in cats and is sporadically reported from humans and other mammalian species. We examined trapped field voles from an endemic area, using a range of diagnostic approaches. These confirmed that a combination of gross and histological examination with culture is most appropriate to identify the true prevalence of the disease, which was shown to be more than 13% at times when older animals that have previously been shown to be more likely to develop the disease dominate the population. The thorough pathological examination of diseased animals showed that voles generally develop systemic disease with most frequent involvement of spleen and liver, followed by skin, lymph nodes, and lungs. The morphology of the lesions was consistent with active disease, and their distribution suggested skin wounds or oral and/or aerogenic infection as the main portal of entry. The demonstration of mycobacteria in open skin lesions, airways, and salivary glands indicated bacterial shedding from the skin and with sputum and saliva. This suggests not only the environment but also direct contact and devouring as likely sources of infection.

A New Phylogenetic Framework for the Animal-adaptedMycobacterium tuberculosisComplex

“…Whereas the ability to cause pulmonary infections is essential for transmission among humans, in other animals, routes of infection other than aerosol transmission seem to play an important role, e.g. grazing contaminated pasture leads probably to a significant proportion of infections by M. bovis in cattle (Phillips et al 2003), M. mungi can transmit directly through abrasions resultant from foraging activity of banded mongoose (Alexander et al 2010, Malone et al 2017), and transmission through skin lesions in M. microti has also been suggested (Kipar et al 2014).…”

Biology and Diseases of Other Rodents

“…; and the blood parasites Babesia microti, Haemobartonella microti, and Trypanosoma microti. Bacterial shedding occurs from the skin, sputum and saliva (Kipar et al, 2013). In addition, various dermatomycoses, rabieslike viruses, and Yersinia pseudotuberculosis have been isolated from voles (Cox, 1979;Ditrich and Otcenasek, 1982;English and Southern, 1967;Sodja et al, 1982;Zhou et al, 2004).…”

Mycobacterial infections and vole bacillus vaccines

“…However, it should be pointed out that while this outbreak was caused by infection with M bovis , feline infections with the vole TB pathogen Mycobacterium microti are far more common in the UK (Smith and others 2009, Kipar and others 2013). …”

“…The most interesting feature of the infection of cats with these two different mycobacterial species is that they occur in geographically distinct locations across Great Britain (Smith and others 2009, Kipar and others 2013). This has led to the proposal that infection with M microti may be protective against infection with M bovis and may explain the epidemiology of bovine TB in the UK (Smith and others 2009).…”

“…As the infection of cats with M microti is thought to be a result of eating infected voles (Smith and others 2009, Kipar and others 2013), we would like to suggest that the oral administration of a M microti vaccine may provide a natural, effective vaccine to the omnivorous badger population. In this context, it should be noted that the original Medical Research Council human TB vaccine trial used two different vaccines, the modified M bovis BCG and the vole bacillus vaccine, M microti , and no significant differences in efficacy between the two vaccines was observed in these trials (D'Arcy-Hart and others 1967).…”