Query: A Journey from Ruminants to Heart Valves

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Last post was all about dogs and their mouths. This time, is about cow placentas. At least to a certain extent. Coxiella burnetii is a gram negative organism that is known to cause a variety of diseases, however it is most commonly associated with culture-negative endocarditis. While it is generally a “wimpy” organism and not very virulent, in the right host, it can case devastating disease with surgical intervention and life-long antibiotics being the only means to control it.

Basics of Microbiology

Coxiella burnetii is a small coccobacillus that has a cell wall similar to that of gram negative bacteria (1) and almost exclusively grows in eukaryotic cells (4), particularly in the acidic phagolysosome. One of the characteristics of C. burnetii is its so-called “phase variation” where its lipopolysaccharide undergoes an antigenic shift (4, 5). Phase I is the “natural phase” that is found in infected animals, arthropods, or humans, which is highly contagious and corresponds to a smooth LPS. Phase II displays a truncated LPS and is a less infectious form of the organism, which is obtained only in laboratoris after serial passages in cell cultures (4,5). This allows someone to use the antibodies against these to figure out if they have an acute or chronic Q fever infection. During acute infection, antibodies against the phase II predominate, while during chronic infection, antibodies to both phases are seen. Like other infectious diseases, IgM will predominate during the initial stages of the disease.

They have been found to survive anywhere from 7 to 10 months on wool in ambient temperature, for more than one month on fresh meat, and for more than 40 months in milk (1). The reservoirs described include cattle, sheep, goats, as well as domestic animals, ticks, and birds. Birth products seem to have the highest concentration of bacteria, and it is classically been described as one of the main routes of transmission, with birth products aerosolizing the bacteria. In ruminants (i.e. cows) the main clinical manifestations are those of infertility, stillbirth, abortion, mastitis, and endometriatis. Shedding has also been seen in cattle from vaginal mucus and milk for up to 2 months (1). 

Human infection has been thought to occur via inhalation, however even indirect exposure such as contaminated laundry or ingestion has been suggested to play a role (2). A review of several outbreaks from the Netherlands found that the highest risk of infection in rural areas occurred within distances of 5-10km of infected farms, while in urban areas, the distance was 2-4km (3). Those who lived within 1km of the source farm had a 46 times larger risk than those living 5-10km away. This review also found that wind plays an important epidemiological role, with wind speeds exceeding 2 m/s being associated with outbreaks. 


The most reliable method for diagnosis is serology, as culturing the organism is difficult enough and one needs a biosafety level 3 lab to perform such studies. The most reliable methods include indirect immunofluorescence, complement fixation, and ELISA, with IFA being the reference method (1). A review highlights that the sensitivity of these serological studies is quite good in cases of chronic Q fever, but it is not as good for the acute version of the disease (6):

It should be noted that the utility of serology depends on the prevalence of the disease in a given population, as most of the cases of Q fever resolve spontaneously. It is entirely possible for healthy folks to have some sort of antibody reaction, so the cut-offs change depending on prevalence. During therapy, phase-I and II antibodies will decrease accordingly. As an example, below is a good way to interpret serology results. As you can see, during the acute fever, phase II antibodies are much higher than phase I, but as the disease approaches its chronic form, phase II and I antibodies have similar levels:

One center in France notes that phase II antibody titer >1:200 indicates recent contact with C. burnetii, while a phase I IgG antibody >1:800 is predictive of chronic infection (4), with IgM persisting anywhere from 6-8months. In the event of acute infection, a 4-fold increase in phase II IgG or IgM antibodies between 2 samples taken anywhere from 3-6 weeks apart is diagnostic (1). Recently, PCR-assays have been evaluated, with one study from the Netherlands using the IS1111 assay having a sensitivity and specificity of 92.2% and 98.9%, respectively (1). While this is not widely available, expect this to be a more predominant diagnostic modality in the future. 

Clinical Manifestations:

In this post, I’ll focus mostly on infective endocarditis because that is a fairly devastating disease in and of itself and it is the one that most people commonly associate with Q fever. Despite this, other forms of acute and chronic Q fever exist. In the northern hemisphere, males tend to be more commonly infected, and these tend to occur during the spring-early summer months. In a Spanish study of 155 cases (7), male-to-female ratio was 4.2:1, with most cases occurring in the spring. Acutely, the most common symptoms include fever, headache, malaise, and cough with most patients presenting with a combination of hepatitis and pneumonia:

Similarly, one large french cohort of over 1300 patients found that most of the cases occurred during the spring months (April – June), with men being the predominant gender infected (male sex ratio of 2.45, 8). 8% were veterinarians, 38% had some rural exposure, and 23% had ingestion of farm goat cheese. Headache, fevers, and myalgias were the most common symptoms:

Within this cohort, 313 cases of chronic Q fever were identified, of which endocarditis accounted for 73% of these:

In another French cohort, the most common clinical form of Q fever was hepatitis (38%), followed by endocarditis (22%), and pneumonia (25%), though flu-like symptoms were also common in acute Q fever (19%, 9). Multivariate analysis found that valvulopathy was strongly associated with chronic Q fever, while findings such as pneumonia, lymphadenitis, thrombosis, were negatively correlated. Q fever pneumonia seems to be correlated with male sex, middle age, high CRP levels, and the presence of headaches according to a prospective study from patients admitted with CAP (10).

Q Fever Endocarditis

When it comes to diagnosing endocarditis, serology plays a role. For instance, one study used the following criteria to diagnose endocarditis (11):

Notably, major criteria also includes chordae tendinae rupture for major criteria with valve thickening being considered a minor criteria. Small studies have established valvulopathy as an important risk factor. For instance, in one cohort of 15 patients with Q fever endocarditis (12), 14 of them had underlying valvulopathy, with 88% presenting with fever and 60% presenting with heart failure. An Australian retrospective cohort evaluated 13 cases with endocarditis, of which 12 had underlying valvular disease (13). Twelve received a combination of doxycycline and hydroxychloroquine. Symptoms included fever, sweats, weight loss, dyspnea, rigors, anorexia, and arthralgias.  Larger studies seem to support this. In a retrospective study of 72 patients with Q fever and echocardiogram results, 31 of these patients had underlying valvulopathy (14). Thirteen did not receive antibiotics and ultimately developed infective endocarditis. Age >40, (HR 1.07), aortic regurgitation (HR 1.2, 95% CI 3.2 to 32.2), and MR (HR 4.78, 95% CI 1.4 to 16) were independently associated with development of endocarditis, while antibiotic prophylaxis was associated with reduced incidence (HR 0.002, 95% CI 0.0-0.77). 

A larger retrospective analysis of 1569 patients with acute Q fever found that previously known valvular abnormalities were associated with increased incidence of IE (OR 438, 95% CI 129-1632), while therapy with Doxycycline and HCQ was actually protective (15):

Prior valvulopathy is not the only risk factor for Q fever endocarditis, as the presence of the lupus anticoagulant has been found to correlate with it. As it so happens, Q fever has a relationship with the lupus anticoagulant and anticardiolipin antibody. These are antibodies that are directed against negatively charged phospholipids and are associated with clotting in vivo, but prolonged PT/PTT in vitro (i.e. clinically, someone will clot while tests will say the patient is going to bleed). A small retrospective study found that 13 out of 17 patients with Q fever tested had positive lupus anticoagulant activity. Antiphospholipid tests were positive in 21 out of 26 patients tested, and all had prolonged aPT and a positive Russell’s viper venom test (16): 

Moreover, in a cohort of 664 patients with Q fever, 13 of them presented with thrombosis (17). In 12/13 cases, aPL antibodies were positive, with the IgG aCL median being 310 GPLU. Overall, IgG aCL levels decreased over the period of 48 months following therapy:

Indeed, those with thrombosis had a higher IgG aCL compared to the Q fever patients without thrombosis (median 18 GPLU). 

Several studies have established the relationship between the aPL antibodies and endocarditis risk. One study evaluated 72 patients with acute Q fever and compared them with healthy controls, patients with endocarditis from another etiology, and patients with valvulopathy without endocarditis (18). The mean levels of IgG aCL were highest in the cohort with endocarditis without C. burnetii infection, however patients with acute Q fever had much higher IgG aCL levels compared to non-Q fever endocarditis

The presence of valvulopathy seemed to be correlated with aCL levels in this study and they were associated with independent progression to endocarditis (OR 5.69, 95% CI 1.16-27.9). Indeed, a cut-off of >90 GLPU was found to be  a predictor of endocarditis.

In another study comparing 9 patients with Q fever endocarditis with those who had valvular heart disease only, the median IgG aCL levels were much higher in the endocarditis cohort, with acute Q fever with vegetations having higher aCL levels than those with chronic endocarditis (19):

Further, multivariate logistic regression in a large French cohort found that aCL were associated with complicated Q fever, including endocarditis:

A previously mentioned study (11) found that factors associated with acute Q fever endocarditis included positive aCLs (OR 2.7, 95% CI 1.3-5.5) and high IgG aCL levels (>90 GPLU, OR 3.4, 95% CI 2-7.5). Indeed, the authors here recommended a TEE in the event of an inconclusive TTE with an aCL level >GPLU and men aged 40 or more:

One review advocates for repeat serology testing after 3 and 6 months of therapy to track anti-phase I IgG and if the level increases beyond 1:800, a TEE is warranted if there are no valve lesions in a prior TTE (20). These two test could be combined to determine the need for the more sensitive TEE, with high aCL antibodies and high anti-phase I IgG being used to make the decision as to proceed with the more invasive test. Unfortunately, I was unable to find such a study though the prolonged duration of antibiotics would at least warrant consideration if there is a rising anti-phase I IgG. 

Long term outcomes for patients with endocarditis was established in a retrospective cohort of 104 patients (21). Independent risk factors related to death were age at diagnosis (HR 1.11, 95% CI 1.05-1.18), stroke at diagnosis (HR 7.09, 95% CI 2025), endocarditis on a prosthetic valve (HR 6.04, 95% CI 1.47-24.8), and absence of a four time decrease in IgG and IgA at 1 year (HR 5.69, 95% CI 1-32.22) and presence of IgM at year 1 (HR 12.08, 95% CI 3.11-46.8):

Further, multivariate Cox regression analysis found that heart failure (HR 2.68) and cardiac abscesses (4.71) were independent factors associated with surgery, while delay of antibiotics more than 12 months (HR 0.2, 95% CI 0.04-0.91) was associated with serological failure. Of 46 valves evaluated, only 3 were positive for culture or immunohistochemistry after 18 months of treatment, with duration <18 months being associated with serological relapse (HR 9.69, 95% CI 1.08-86.7).  

If I were to summarize this section, it would be to “watch out for older men with prosthetic or valvular lesions, high anti-phase I IgG and elevated aPL levels” as these are at high risk for endocarditis.


I alluded to this above, but the backbone of therapy is the combination of tetracyclines (usually doxycycline) and hydroxychloroquine. I mentioned previously the intra-cellular nature of the organism and its ability to withstand the fairly acidic environment of the phagolysosome. This makes the bug resistant to most antibiotics, as they can be inactivated by the acidic environments. One review highlights that treatment with a tetracycline reduced fever by 50% in one study, with doxycycline having a much better effect than tetracycline (22). Doxycycline and TMP-SMX combined with rifampin have been used, however drug interactions prevent the prolonged duration of therapy with rifampin. The standard dose of doxycycline is 100mg twice per day, but in certain situations, higher doses have been used. In one retrospective study, doses of 300-400mg per day were used in patients who had slow serological response (decrease of less than two dilutions in one year) and these patients achieved  a mean decrease of phase I antibodies from 0.42 to 3.42 after the dose increase (23). A retrospective cohort evaluated 14 patients who received doxycycline and ofloxacin and 21 doxycycline and HCQ for the treatment of Q fever endocarditis (24). While the mortality rate was similar, the HCQ cohort had a shorter duration of therapy and had significantly lower rates of relapse:

This is likely due to HCQ alkalinizing intracellular phagolysosomes. As a result, the standard of therapy for endocarditis and for prophylaxis is HCQ 200mg daily and doxycycline, for at least 18 months and sometimes up to 2 years. Cure is considered when IgG phase I antibody levels are <1:800, and IgM and IgA titers are <1:50 (2). Serologies being positive 10 years out has been seen despite therapy with doxycycline, though it should be noted this was monotherapy with spotty adherence (25):


  • C. burnetii is an intracellular gram negative organism typically seen in cattle, and it is responsible for multiple gynecological issues in animals such as stilbirths and spontaneous abortions
  • It undergoes phase variation, with phase I being more virulent than phase II
  • Serology is the mainstay for diagnosis
  • Humans are usually infected via inhalation of aerosols
  • Diseases range from flu-like symptoms, pneumonia, hepatitis, to chronic Q fever such as endocarditis as well as osteomyelitis
  • Older age, male sex, positive antiphospholipid syndrome, and the presence of valvulopathy are associated wit the development of endocarditis
  • Treatment consists of doxycycline and HCQ (the latter to alkalinize the phagolysosome) for at least 18 months, sometimes longer


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