burnetii DNA; however, only 2 samples were ST20 (Figure 1 and Table 3). Of the caprine samples, 28 were ST8 and ten were likely ST8. Two samples were neither ST8 nor ST20, however low DNA concentrations did not allow determination of the exact sequence type (Table 3). Discussion Our results show that the current distribution of C. burnetii is the result of a few highly VX-809 mouse fit clones that appear to be largely
confined to individual livestock species. The concept of distinct clades associated with species specific restrictions may explain the low apparent rate of clinical disease among human populations despite the high prevalence of these bacteria. Among our samples, two sequence types were highly prevalent: ST8 was exclusively found in samples from goats while ST20 dominated cow’s milk with only two examples of ST20 from goats. This pattern is consistent with other smaller studies where likely ST20 isolates (see below) were from cattle [21, 27, 28] and rarely from goats: a single ST20 sample attributed to a goat in France  and abortions in a large commercial dairy goat herd in the UK . Likewise, recent ST8
samples have been collected from sheep, goats and humans [21, 27, 30, 31]. This tendency for host restriction may be the result of a stochastic introduction into a large livestock population allowing for an increase in frequency, spread through trade, but constrained to that population through anthropogenic isolation of livestock species. However, Selonsertib as both selleck chemical genotypes show a tendency for host restriction and similar patterns are found in Europe [21, 27, 28, 30] as well Teicoplanin as the USA, it seems more likely that these genotypes are evolutionarily adapted to certain host species. Genotyping historical collections of C. burnetii has provided a baseline for environmental
distribution of sequence types [17, 19, 20, 32]. Interestingly, contemporary sampling yields only a small subset of the known genotypes, many of which are found across multiple studies [21, 27, 28, 30] (Kersh et al., Genotypes of Coxiella burnetii strains found in the United States environment, 2006-2008, in preparation). In some cases, subtypes of the same MST genotypes were identified [27, 30, 33]. Consistent with these findings, our genotyping of milk samples revealed only three or four MST genotypes; while only two samples had unknown genotypes (and may both have the same genotype), the genotypes of all other samples are likely to be either ST20 or ST8. It is important to note that additional genotypes not detected by our sampling may be circulating at very low levels. A high proportion of recent milk, placenta, and mucus samples from goat, cow and sheep farms in Spain were ST20, but none were ST8 . Kersh et al. recently genotyped C. burnetii DNA from US environmental samples and found ST8, ST16/26, and ST20 genotypes. Samples associated with goats were ST8 and all ST20 samples came from cattle dairies (Kersh et al.