High prevalence and two dominant host-specific genotypes of Coxiella burnetii in U.S. milk

Abstract

BackgroundCoxiella burnetii causes Q fever in humans and Coxiellosis in animals; symptoms range from general malaise to fever, pneumonia, endocarditis and death. Livestock are a significant source of human infection as they shed C. burnetii cells in birth tissues, milk, urine and feces. Although prevalence of C. burnetii is high, few Q fever cases are reported in the U.S. and we have a limited understanding of their connectedness due to difficulties in genotyping. Here, we develop canonical SNP genotyping assays to evaluate spatial and temporal relationships among C. burnetii environmental samples and compare them across studies. Given the genotypic diversity of historical collections, we hypothesized that the current enzootic of Coxiellosis is caused by multiple circulating genotypes. We collected A) 23 milk samples from a single bovine herd, B) 134 commercial bovine and caprine milk samples from across the U.S., and C) 400 bovine and caprine samples from six milk processing plants over three years.ResultsWe detected C. burnetii DNA in 96% of samples with no variance over time. We genotyped 88.5% of positive samples; bovine milk contained only a single genotype (ST20) and caprine milk was dominated by a second type (mostly ST8).ConclusionsThe high prevalence and lack of genotypic diversity is consistent with a model of rapid spread and persistence. The segregation of genotypes between host species is indicative of species-specific adaptations or dissemination barriers and may offer insights into the relative lack of human cases and characterizing genotypes.

Coxiella burnetii Infects Primary Bovine Macrophages and Limits Their Host Cell Response

“…Although cattle are not the main source of human infection, the bovine macrophage model established and characterized here can be used to study host-pathogen interactions in a reservoir host at the cellular level, allowing to characterize replication and the pathogen-induced host cell response to different C. burnetii strains, e.g., the species-specific adaptations of the highly prevalent C. burnetii genotype ST 20 recently identified in bovine milk in the United States (74).…”

Right on Q: Genetics begin to Unravel Coxiella Burnetii host cell Interactions

“…In the USA, millions of dairy cows appear exclusively infected with genotype 20 strains. However, despite tremendous shedding of these strains into the environment, they have not been isolated from human Q fever cases and thus may be attenuated in causing human disease [20].…”

Single Nucleotide Polymorphism Genotyping and Distribution of Coxiella burnetii Strains from Field Samples in Belgium

“…During the Q fever epidemic that occurred in The Netherlands between 2007 and 2010, C. burnetii genotyping was successfully applied to identify isolates circulating in infected dairy goat farms and in human cases (13)(14)(15). Genotyping is also useful under nonepidemic conditions to obtain an inventory of the main strains circulating among livestock (16)(17)(18). Different genotyping techniques have been described and used in different epidemiological contexts without any being a reference method.…”

“…The multilocus variable-number tandem-repeat analysis (MLVA) is probably the most sensitive technique, but it is criticized for producing results that are too discriminatory and difficult to compare between countries (19). Other typing methods are used for C. burnetii, including single nucleotide polymorphism (SNP) analysis because of its rapidity and easy interpretation of results (14,16).…”