Coxiella burnetti

Question 1

What type of bacteria is Coxiella burnetii?

Answer 1

C. burnetii is a ubiquitous, small, pleomorphic, intracellular Gram-negative bacterium.

Question 2

How do infections of C. burnetii occur?

Answer 2

Inhalation, ingestion, sometimes through blood transfusion `

Question 3

C. burnetii causes what clinical diseases?

Answer 3

Late-term abortion, still birth, birth of weak offspring (all in small ruminants)

Rarely abortion or reproductive failure in cattle

Question 4

Where is C. burnetii in clinical or nonclinical animals shed?

Answer 4

C. burnetii can be found in placental membranes, fetuses and uterine fluids, but also be shed by clinically unaffected animals

Question 5

Where does C. burnetii replicate?

Answer 5

C. burnetii replicates within trophoblasts of the placenta and after the logarithmic growth phase, produces a spore-like bacterial form termed small cell variant (SCV).

SCV are responsible for persistence of the organism in dust, manure and the air of farms

Question 6

What ways can C. burnetii be diagnosed? What does a positive or negative mean?

Answer 6

Positive Ab titer is evidence of current or previous infection. BUT seronegative animals can be actively shedding the organism. Serologic tests evaluate Ab to two distinct antigenic forms of C. burnetii called phase I and phase II.

PCR kits are available - target gene is IS1111

Bulk tank milk PCR also appears to be good agreement between seroprevalence and BTM Ab concentration in dairy sheep flocks, has been consistent in dairy cattle and dairy goats.

ELISA is preferred for large-scale screening of the infection status in livestock. This can be used on serum, plasma and milk of ruminant.

Question 7

How is quantitative PCR helpful when determining if C. burnetii is the most likely cause of abortion?

Answer 7

Animals with abortion due to C. burnetii have much higher qtPCR values that correspond to several orders of magnitude greater quantities of organisms than those associated with asymptomatic long-term shedding or environmental contamination.

Question 8

What limits the utility of PCR as prepartum assessment of an animal’s risk of abortion or post-partum shedding?

Answer 8

Before aborting, shedding of bacteria in vaginal fluids is absent or minimal, even when bacterial counts in utero are substantial.

Question 9

What’s the difference between cattle and goats in regard to shedding of C. burnetii?

Answer 9

In cattle, vaginal shedding is typically very short, while shedding in milk occurs for much longer periods.

In goats, milk shedding patterns are similar to vaginal shedding but with lower numbers of pathogens and for longer periods ( > 8 weeks). Level of vaginal shedding typically decreases by 2-3 weeks.

Question 10

What has been assoc. with lower risk of seropositivity in ruminants?

Answer 10

1. Quarantine of new animals entering the farm
2. Use of stringent hygiene measures for visitors
3. Limited introduction of new animals
4. Prompt removal of birth materials immediately postpartum
5. Frequent cleaning or changing of bedding

Question 11

How persistent is C. burnetii in the environment?

Answer 11

Profoundly resistant to environmental stress, desiccation, and commonly used disinfectants. Can survive in the environment for prolonged periods of time.

Question 12

What are measures to implement to control transmission, environmental contamination and consequently minimize zoonotic risk?

Answer 12

1. Segregate periparturient animals from other high-risk animals.
2. Manage parturient animals in an enclosed environment with controlled airflow to lower risk for down-wind transmission.
3. Eliminate land application of fresh manure.
4. Compost manure for 90 days before land application.
5. Promptly remove and discard aborted fetus and uterine fluids either by closed composting or burning
6. Move naïve or gestating animals to areas of the farm that are upwind of aborting animals
7. Minimize development of excessively dry and dusty environments in animal housing areas.