BW-ch10.pdf

Q Fever

Chapter 10

Q FEVER

DAVID M. WAAG, P h D *

INTRODUCTION

HISTORY

MILITARY RELEVANCE

INFECTIOUS AGENT

Disinfection

Pasteurization

Irradiation

DISEASE

Epidemiology

Pathogenesis

Infection (Coxiellosis) in Animals

Clinical Disease in Humans

DIAGNOSIS

Serology

Culture

TREATMENT

PROPHYLAXIS

SUMMARY

* Microbiologist, Division of Bacteriology, US Army Medical Research Institute of Infectious Diseases, 1425 Porter Street, Fort Detrick, Maryland

21702

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Medical Aspects of Biological Warfare

INTRODUCTION

Q fever was discovered in Australia and in the

United States before the outbreak of World War II. In

Australia the disease was common in slaughterhouse

workers and farm workers, 1 and it persists as an oc-

cupational problem. 2 This zoonotic disease is nearly

worldwide and the etiologic agent, Coxiella burnetii,

has a broad host range. Acute Q fever, although rarely

life-threatening, can be temporarily incapacitating.

Humans usually contract the disease by inhaling barn-

yard dust contaminated after parturition by infected

animals. A single microorganism is sufficient to cause

infection. The infectious particle is extremely resistant

to environmental degradation. Acute disease is not ac-

companied by unique symptoms. Therefore, Q fever

must be considered in the differential diagnosis when a

history of animal contact is established. Rarely, acute Q

fever progresses to chronic Q fever, a debilitating, life-

threatening infection that is difficult to treat. Because

of its high infectivity and stability in the environment,

C burnetii is listed as a Category B biothreat agent.

HISTORY

In 1933 a disease of unknown origin was first

observed in slaughterhouse workers in Queensland,

Australia. Patients presented with fever, headache, and

malaise. Serologic tests for a wide variety of possible

etiologic agents were negative. 1 Because the disease

had an unknown etiology, it was given the name Q

fever (for query). The infection was shown to be trans-

missible when blood and urine from patients elicited

a febrile response after injection into guinea pigs. The

infection could be passed to successive animals. Un-

fortunately, no isolate could be obtained after culture

on bacteriological media, and the etiologic agent was

thought to be a virus.

About this time, ticks were being collected in west-

ern Montana as part of an ongoing investigation into

Rocky Mountain spotted fever. Ticks collected from

the Nine Mile Creek area caused a febrile response

when placed onto guinea pigs. The infection could

be passed to successive guinea pigs through injection

of blood. 3 Examination of inflammatory cells from

infected guinea pigs revealed rickettsia-like microor-

ganisms, although the disease in guinea pigs was not

spotted fever. 4 A breakthrough in cultivating this agent

occurred with the discovery that it would grow in yolk

sacs of fertilized hens’ eggs. 5 Although the microorgan-

ism was demonstrated to be infectious, the disease it

caused was unknown. In Australia, however, a disease

was identified, but it had an unknown etiology.

In Montana a researcher was infected while working

with the Nine Mile isolate, and guinea pigs could be

infected by injecting a sample of the patient’s blood.

At the same time, infected mouse spleens were sent

from Australia to the United States. In a remarkable

mix of serendipity and science, it was confirmed that

the agent causing Q fever and the Nine Mile isolate

were the same by demonstrating that guinea pigs

previously challenged with the Nine Mile isolate were

resistant to challenge with the Q fever agent. 6 The

conclusion could also be made that ticks transmitted

Q fever. Although initially named Rickettsia diaporica 7

and Rickettsia burnetii , 8 the microorganism was given

the name C burnetii in 1948 in honor of Dr Cox and Dr

Burnet, who made important contributions regarding

propagation and isolation of this agent. 9

Investigations of Q fever soon established that C

burnetii was prevalent in slaughterhouses and haz-

ardous in the laboratory, and also could be spread

by aerosol. 10,11 The successful culture of the Q fever

organism in chicken embryos proved to be a fortuitous

breakthrough for advances in Q fever research, as well

as for other rickettsial organisms. 12 Q fever has been

identified in over 50 countries. 13

MILITARY RELEVANCE

An atypical pneumonia, similar to Q fever, was

noted in German soldiers in Serbia and southern

Yugoslavia during World War II. 14 The agent causing

“balkengrippe” was not confirmed by laboratory test-

ing, but the clinical and epidemiological features of the

illness described were most consistent with Q fever.

Hundreds of cases were observed in German troops

in Italy, Crimea, Greece, Ukraine, and Corsica. Five Q

fever outbreaks were also noted in American troops

in Europe during the winter of 1944 and the spring

of 1945. 14 Cases usually occurred in troops occupying

farm buildings recently or concurrently inhabited by

farm animals. 15 However, cases also occurred in the

absence of close contact with livestock. At an airbase

in southern Italy, 1,700 troops became infected, pre-

sumably as a result of infected sheep and goats being

pastured nearby. 16

More recent Q fever cases in military service mem-

bers have also occurred. An acute Q fever outbreak

associated with a spontaneous abortion epidemic in

sheep and goats occurred in British troops deployed

in Cyprus, American airmen in Libya, and French

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Q Fever

soldiers in Algeria, causing 78 cases of illness. 14,17,18 Q

fever outbreaks were also reported in Swiss and Greek

soldiers and Royal Air Force airmen. 14 Q fever has been

identified in American military personnel in the Per-

sian Gulf War. One case of meningoencephalitis associ-

ated with acute Q fever was reported in a soldier who

recently returned from the Persian Gulf. 19 Subsequent

serologic testing in the author’s laboratory identified

three additional acute seroconversions in soldiers of

the same battalion. These reports underscore the neces-

sity of considering the possibility of Q fever in service

members having symptoms consistent with a Q fever

and a recent history of exposure to livestock that may

harbor C burnetii.

INFECTIOUS AGENT

C burnetii is an obligate intracellular pathogen of

eukaryotic cells and replicates only within the phagoly-

sosomal vacuoles of host cells, primarily macrophages.

Growth does not occur on any axenic medium. During

natural infections, the organism grows to high titer in

placental tissues of goats, sheep, and possibly cows. 20,21

This microorganism is routinely cultured in chicken

embryo yolk sacs and in cell cultures, 22 and it can also

be recovered in large numbers within spleens of ex-

perimentally infected mice and guinea pigs. 22 Growth

is slow, with a generation time longer than 8 hours. 23

The microorganism usually grows as a small cocco-

bacillus, approximately 0.8 to 1.0 µm long by 0.3 to 0.5

µm wide. Like other gram-negative microorganisms, C

burnetii possesses a lipopolysaccharide (LPS), although

the Gram stain reaction is variable. 24,25 LPS is important

in virulence and is responsible for the antigenic phase

variation seen in this organism. 26,27 C burnetii can dis-

play LPS variations similar to the smooth-rough LPS

variation in Escherichia coli. 26 Bacterial isolates from

eukaryotic hosts have a phase I (smooth) LPS character,

which can protect the organism from microbicidal ac-

tivities of the host. As those isolates are passed in yolk

sacs or other nonimmunocompetent hosts, the phase

I LPS character of the bacterial population gradually

changes to the phase II (rough) form. Phase I micro-

organisms are virulent, and phase II microorganisms

are avirulent in immune competent hosts.

The developmental cycle features small, compacted

cell types within mature populations growing in animal

hosts. 28 These forms, called small cell variants (SCVs),

are responsible for the organism’s high infectivity,

as well as its capability to survive relatively extreme

environmental conditions; its chemical resistance; and

its resistance to desiccation, heat, sonication, and pres-

sure. 29 The large cell variants (LCVs) are probably the

metabolically active cells of this organism. The SCV and

LCV are antigenically different. 30 Transition between

SCV and LCV does not involve classical phase variation,

which refers to LPS structure, but can be accompanied

by changes in the expression of surface protein.

Coxiella is an obligate intraphagolysosomal parasite

with acid-activated metabolism, presumably because

most of its transport mechanisms required for import

of required nutrient substrates from the vacuole envi-

ronment function in a pH range of 4.0 to 5.5. Purified

organisms incubated without any host fractions or

cells require an acid pH to transport or metabolize

either glucose or glutamate. 31 However, in-vitro growth

under acidic conditions has not resulted in axenic

growth, although protein synthesis can occur. Growth

in the harsh phagolysosomal environment shows that

this microorganism has coping strategies. The coping

mechanism, although undefined, may involve the pro-

duction of oxygen scavengers. 32 An iron/manganese

superoxide dismutase has been demonstrated, and

genetic sequencing has also revealed a copper-zinc

dismutase. 33 Because C burnetii is susceptible to reac-

tive oxygen and nitrogen intermediates produced in

response to infection by the host cells, 34 the microor-

ganism’s primary strategy for surviving within host

cells is likely avoiding host cell activation. That phase

I C burnetii does not activate human dendritic cells, 35

and that C burnetii LPS does not activate host antimi-

crobial responses via Toll-like receptor 4, are evidence

to support this strategy. 36

Disinfection

Ten percent household bleach did not kill the or-

ganisms during a 30-minute exposure. 37 Likewise,

exposure to 5% Lysol, 2% Roccal, or 5% formalin for 30

minutes did not inactivate C burnetii . 37 The organism

was inactivated within 30 minutes by exposure to 70%

ethyl alcohol, 5% chloroform, or 5% Enviro-Chem. 37

(The latter chemical, a formulation of two quaternary

ammonium compounds, is known as Micro-Chem Plus

and is available through National Chemical Laborato-

ries, Philadelphia, Pa.) Formaldehyde gas can also be

an effective sterilizing agent when administered in a

humidified (80% relative humidity) environment. 37

Pasteurization

The frequent presence of C burnetii in cow’s milk led

to the establishment of effective milk pasteurization

procedures. Temperatures of 61.7 o C for 20 minutes

can kill the organisms in raw milk. 38 In the laboratory,

aqueous suspensions of the microorganism are typi-

cally killed by treating at 80 o C for 1 hour.

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Medical Aspects of Biological Warfare

Irradiation

serum samples. An important consideration is that

useful biological specimens are not degraded after

activation by irradiation. Gamma irradiation (2.1 x

10 6 rads) was shown to have no deleterious effect on

the antibody-binding capacity of C burnetii antigen,

the antigen-binding capability of anti- C burnetii anti-

body, the morphological appearance of C burnetii by

electron microscopy, or the distribution of a major

surface antigen. 39

Gamma irradiation can be used to sterilize biologi-

cal preparations. The amount of gamma irradiation

that reduced infectivity by 90% was 8.9 x 10 4 rads

for C burnetii suspended in yolk sacs and 6.4 x 10 4

rads for the purified specimen. 39 The sterilizing dose

was calculated to be 6.6 x 10 5 rads. Typically an ir-

radiation dose of 2.1 x 10 6 rads is used for sterilizing

DISEASE

Epidemiology

that 15% of the general population surveyed and 32%

of goat owners had serologic evidence of infection. 56

The incidence of reported Q fever is higher now than

in the 1990s, partly because of improved surveillance

and more accessible testing.

Researchers find it controversial whether bacterial

strains causing chronic Q fever are fundamentally

different from strains causing acute Q fever. Some

evidence suggested a link between genetic structure

and the disease type (chronic or acute), 57 but other re-

searchers thought that host-specific factors were more

important. 58 The lack of a good chronic Q fever animal

model made it difficult to resolve the question. How-

ever, a recent genetic analysis showed that groupings

based on allelic differences of 159 C burnetii isolates

from chronic Q fever cases were never found associated

with acute disease. 59 This observation strengthens the

case that the disease course in humans can be related

to the strain of the infecting microorganism.

Q fever is a zoonotic disease that occurs world-

wide. Of the variety of species that can be infected

by C burnetii , humans are the only species to develop

symptomatic disease. Human infections are primar-

ily found in persons occupationally exposed, such as

ranchers, veterinarians, and workers in meatpacking

plants. Domestic ungulates, such as cattle, sheep, and

goats, usually acquire and transmit C burnetii , and

domestic pets (primarily cats) can be a primary source

of human infection in urban environments. 40-42 Heavy

concentrations of microorganisms are secreted in milk,

urine, feces, and especially in parturient products of

infected pregnant animals. 43 Because of the stability

of this agent, dried, infectious particles in barnyards,

pastures, and stalls can be a source of infection months

later. 43 Infection is most commonly acquired by breath-

ing infectious aerosols or contaminated dust. 44 Patients

can also be infected by ingesting contaminated milk 45

and through the bite of an infected tick. 3 Infection can

also occur in individuals not having direct contact with

infected animals, such as persons living along a road

used by farm vehicles 46 or those handling contami-

nated clothing. 47,48

C burnetii is extremely infectious for humans. The

infectious dose is estimated to be 10 microorganisms

or fewer. 49 The route of infection may determine the

clinical manifestations of the disease. 50 In most cases

of infections acquired by ingesting the microorganism,

acute Q fever is found primarily as a granulomatous

hepatitis. 51 However, in patients infected by the aero-

sol route, Q fever pneumonia is more common. 52 The

infectious doses have been shown to vary inversely

with the length of the incubation period. 53 Person-to-

person transmission has been reported, but is rare. 54

The rates of Q fever seropositivity vary. In Nova Scotia,

where extensive seroepidemiological work has been

done, 14% of tested human samples were positive. 55

Overall, the incidence of Q fever is underreported. For

example, in Michigan, although the first two Q fever

cases were not reported until 1984, a survey showed

Pathogenesis

Q fever is an acute, self-limited systemic illness

that can develop into a chronic, debilitating disease.

Pathogenesis of infection in human disease is not well

defined. Studies with animal models show that after

initial infection of the target organ, the microorganism

is engulfed by resident macrophages and transported

systemically. The acidic conditions within the pha-

golysosome allow cell growth. Eventually proliferation

within the phagolysosome leads to rupture of the host

cell and infection of a new population of host cells. In

animal models, the spleen and liver and other tissues of

the reticuloendothelial system appear to be most heav-

ily infected, which is likely the case in human infection.

Chronic Q fever cases can arise years after the initial

presentation. Animals frequently remain infected over

their lifespans, with outgrowth of the microorganism oc-

curring during conditions of immunosuppression, such

as parturition, 60 or in laboratory animals that have been

immunosuppressed. 61 One of the unresolved mysteries

of Q fever is where the microorganism is “hiding out”

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Q Fever

in the intervening time between recovery from human

acute disease and the development of chronic disease.

Another unresolved question is whether humans ever

completely clear the microorganism after infection.

Coxiella DNA has been found in the bone marrow of the

majority of patients who had primary Q fever 12 years

previously. 62 Asymptomatic animals may also harbor

the microorganism. 63

dose. 53,75 There are no characteristic symptoms of Q

fever, but certain signs and symptoms tend to be more

prevalent. Fever, severe headache, and chills are the

symptoms most commonly seen. Fever usually peaks

at 40 o C and lasts approximately 13 days. 76 Fatigue and

sweats are also frequently found. 77 Cough, nausea,

vomiting, myalgia, arthralgia, chest pain, hepatitis, and

occasionally, splenomegaly, osteomyelitis, and menin-

goencephalitis are also associated with acute Q fever. 19,77

Blood tests show a normal white blood cell count, al-

though thrombocytopenia or mild anemia may be pres-

ent. 78 The erythrocyte sedimentation rate is frequently

elevated. 79 Neurological symptoms, such as hallucina-

tions, dysphasia, hemi-facial pain, diplopia, and dys-

arthria, have been described in an outbreak of acute Q

fever. 78 The duration of symptoms increases with age. 76

Pneumonia is a common clinical presentation of

acute Q fever. 80 Atypical pneumonia is most frequent,

and asymptomatic patients can also exhibit radiologic

changes that are usually nonspecific and can include

rounded opacities and hilar adenopathy. 40,81 Infection

can also cause acute granulomatous hepatitis with corre-

sponding elevations of the aspirate transaminase and/or

alanine transaminase. 77 Elevations in levels of alkaline

phosphatase and total bilirubin are seen less commonly.

Chronic Q fever is rarer, but also results in more

deaths than acute Q fever. Patients with prior coronary

disease or patients immunocompromised because of

disease, such as AIDS, or therapy, such as immuno-

suppressive cancer therapy or antirejection therapy

after organ transplant, are more at risk for developing

chronic Q fever. 82,83 Endocarditis, primarily of the aortic

and mitral valves, 84 is the most common manifesta-

tion of chronic Q fever; although chronic hepatitis 85

and infection of surgical lesions 86 have been seen. Ap-

proximately 90% of Q fever endocarditis patients have

preexisting valvular heart disease. 87 Of those acute Q

fever patients with cardiac valve abnormalities, as

many as one third develop endocarditis. 88 Patients with

chronic Q fever lack T-cell responses, resulting in an

immune response inadequate to eradicate the micro-

organism. This immunosuppression of host cellular

immune responses is caused by a cell-associated im-

munosuppressive complex. 89 This complex may cause

immunosuppression by stimulating the production

of prostaglandin E2 and high levels of tumor necrosis

factor, which may also have deleterious effects on the

host. 90-92 Patients with chronic Q fever also have an

increase in interleukin 10 secretion. 93 Suppression of

host immunity may allow persistence of the microor-

ganism in host cells during the development of chronic

Q fever. Other pathological effects of chronic Q fever

include the presence of circulating immune complexes,

resulting in glomerulonephritis. 94

Infection (Coxiellosis) in Animals

Coxiellosis is a zoonosis that affects native and

domestic animals. Animals are infected by biting ec-

toparasites, primarily ticks, and by inhaling infectious

particles. 64 Nursing calves can also be infected via their

mother’s milk—over 90% of dairy herds in the north-

eastern United States were found to be infected with C

burnetii , based on surveillance of bulk milk samples. 65

Pasteurization of milk products decreases the risk of

human infection. Infected animals generally appear

to be asymptomatic, except for a rise in the rate of

spontaneous abortions. 66 Domestic ruminants are the

primary source of infection for humans. Eradication

of Coxiella infection in animal populations is difficult

because infection rarely causes symptoms. Unlike in

humans, infection in animals does not cause patho-

logical changes in the lungs, heart, or liver. The site

most often affected is the female reproductive system,

primarily the placenta, where damage is minimal.

However, infection results in shedding vast quantities

of organisms into the environment, which becomes a

source of infection for other animals and humans.

Sheep have been a source of infection at medical

research institutions, where animals used in neonatal

research have caused Q fever in humans. 67-69 However,

unlike cattle and goats that tend to remain chronically

infected, 70 sheep likely do not shed the organisms into

the environment over a long period. 64,71,72 Therefore,

Coxiella infection in sheep might be a transient infection

with a spontaneous cure, similar to most Q fever cases

in humans. 64 Abortion is seen more often in infected

sheep and goats than in cows. 73

Clinical Disease in Humans

The majority of human C burnetii infections are

asymptomatic, especially among high-risk groups,

such as veterinary and slaughterhouse workers, other

livestock handlers, and laboratory workers. 74 The vast

majority of the overt disease cases are acute Q fever.

Fatalities in acute Q fever cases are rare, with fewer than

1% of cases resulting in death. 1 The incubation period

can last a few days to several weeks, and the severity

of infection varies in direct proportion to the infectious

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