Q fever

Japanese: Q熱

Definition, concept, and etiologyQ fever is a zoonotic disease caused by Coxiella burnetii, a pathogen of the Coxiella genus closely related to Rickettsiae, Legionella, and Chlamydiae, which is transmitted by inhaling aerosols produced when the secretions and excrement of carrier animals such as wild animals, livestock, and pets dry and break down. Depending on the amount of bacteria infecting, approximately half of cases end with asymptomatic infection, and human-to-human infection is rare. The name of the disease comes from a report in 1937 of a mass outbreak of a fever of unknown cause (query) at a slaughterhouse in Brisbane, Australia, called "Q fever," meaning "strange fever."
Epidemiology: Q fever is currently known to be distributed almost worldwide. The first clinical case reported in Japan was in 1989, which prompted various research studies to be carried out, and it is thought that in acute pneumonia, the most common type of disease, it accounts for approximately 2-4% of the bacteria causing community-acquired pneumonia, as in Europe and the United States. In other words, Streptococcus pneumoniae is the most common cause of community-acquired pneumonia, followed by Haemophilus influenzae, Mycoplasma pneumoniae, and Chlamydia pneumoniae, with this bacterium ranking 5th to 7th with a frequency similar to that of Legionella and other bacteria.
Disease type, symptoms, course, and prognosis: The majority of cases of Q fever are acute (acute Q fever). After an incubation period of 1-3 weeks, a variety of symptoms, including influenza-like upper respiratory tract infection, pneumonia, hepatitis, and fever of unknown origin, appear, along with dry cough, high fever, muscle pain, generalized malaise, and transient liver damage. Mortality is 1-2% even without treatment, and is well below 1% if antibiotics are administered appropriately, although there are severe cases of cerebrospinal meningitis, myocarditis, and renal failure. On the other hand, there are a small number of chronic cases with poor prognosis that develop into endocarditis, chronic hepatitis, chronic osteomyelitis, arthritis, and chronic nephritis, and some cases have progressed to chronic fatigue syndrome after acute Q fever.
Examination, diagnosis, and differential diagnosisAcute Q fever, like other atypical pneumonias, has severe clinical symptoms but no significant changes in laboratory test values, and there is little increase in white blood cell count. Chest X-rays in pneumonia cases often show multiple patchy shadows in the lung fields, but there are also cases with a variety of shadows, including interstitial shadows and pleural effusion. Differentiation from bacterial pneumonia caused by Streptococcus pneumoniae and other bacteria is somewhat difficult. Even if symptoms improve, in many cases it takes time for the shadows to improve or resolve, and there are cases where clinical differentiation from organizing pneumonia is necessary.
A definitive diagnosis is made by a four-fold or greater increase in the titers of paired serum antibodies (IgG and IgM), but in many cases it takes several months for the antibody titers to increase. Although ELISA is also used to measure antibody titers, the standard method for measuring antibody titers is the indirect fluorescent antibody test (IFA). PCR detection of the Coxiella gene using respiratory tract samples is a useful auxiliary diagnostic method. This bacterium is highly infectious, requiring management at the P3 level, so culturing it in ordinary hospital laboratories is dangerous.
Treatment and prevention: Most cases of acute Q fever have a good prognosis, but some may develop severe symptoms or progress to a chronic form, so definitive or highly suspected cases should be treated aggressively. β-lactam drugs, which are poorly internalized, are usually ineffective against this obligately intracellular parasite, and tetracycline drugs, which are well internalized, are the first choice. Macrolides and quinolones are slightly less effective. In most cases, fever subsides within a few days of starting treatment, but as with other atypical pneumonias, all drugs require treatment for 2 to 3 weeks.
In Japan, awareness of Q fever is low, so vaccines are not widely used. In Europe and the United States, vaccines for livestock and humans are in practical use, but the application of vaccines to humans is limited to groups that have frequent contact with carrier animals, such as employees of slaughterhouses and dairy farms, veterinarians, and employees of animal experiment facilities. [Akira Watanabe]
■ References
Maurin M, Raoult D: Q fever. Clin Microbiol Rev, 12: 518-553, 1999.
Hiroshi Takahashi, Akira Watanabe: 44. Q fever [Coxiella burnetii]. The current meaning of pathogenic bacteria, 4th revised edition (edited by Keizo Matsumoto), pp.726-738, Medical Journal Co., Osaka, 2011.

Source : Internal Medicine, 10th Edition About Internal Medicine, 10th Edition Information

Japanese:

定義・概念・病因
　Q熱は，リケッチアやレジオネラ，クラミジアに近縁の病原体であるコクシエラ属のCoxiella burnetiiが，保菌動物である野生動物や家畜，ペットなどの分泌物や排泄物が乾燥・崩壊して生じるエアゾルを経気道吸入して感染する人獣共通感染症である．感染菌量にもよるが約半数は不顕性感染で終わり，ヒト-ヒト間の感染はまれである．病名は，オーストラリア・ブリスベンの屠畜場で集団発生した原因不明（query）の熱性疾患が「奇妙な熱性疾患」を意味する「Q fever」として1937年に報告されたことに由来する．
疫学
　Q熱は現在，ほぼ世界中に分布することが知られている．日本の臨床報告第1例は1989年であるが，これを契機に種々の調査研究が行われ，病型として最も多い急性肺炎では，欧米と同様に市中肺炎原因菌の2～4％程度を占めると考えられる．すなわち，市中肺炎では肺炎球菌が最も多く，ついでインフルエンザ菌，肺炎マイコプラズマ，肺炎クラミジアが続き，本菌はその後の第5位～7位前後にレジオネラなどと同程度の頻度で関与する．
病型・症状・経過・予後
　Q熱の大部分は急性型（急性Q熱）である．1～3週間の潜伏期後にインフルエンザ様の上気道炎や肺炎，肝炎，不明熱など多彩な病像で発症し，乾性咳や高熱，筋肉痛や全身倦怠感，一過性肝障害を伴う．死亡率は，無治療でも1～2％であり，抗菌薬が適切に投与されれば１％をはるかに下回るが，脳脊髄膜炎，心筋炎，腎不全となる重症例もある．一方，心内膜炎や慢性肝炎，慢性骨髄炎，関節炎，慢性腎炎などで発症する予後不良の慢性型も少数ながら存在し，急性Q熱の後に慢性疲労症候群様に経過する症例もあるとされる．
検査・診断・鑑別診断
　急性Q熱では，ほかの非定型肺炎と同様，臨床症状が強いのに対して臨床検査値の変化は大きくはなく，白血球数増加なども少ない．肺炎例の胸部Ｘ線像は多発性の肺野斑状影を呈する例が多いが，間質性陰影，胸水貯留など多彩な陰影の例もみられる．肺炎球菌などによる細菌性肺炎との鑑別はやや困難である．症状が改善しても陰影の改善・吸収には時間を要する例が多く，臨床的には器質化肺炎との鑑別を必要とする例がある．
　確定診断は，ペア血清抗体（IgGおよびIgM）価の4倍以上の上昇によるが，抗体価の上昇に数カ月を要する例も多い．ELISA法による抗体価測定法もあるが，抗体価測定の標準法は間接蛍光抗体法（IFA法）である．気道系の検体を用いるコクシエラ遺伝子のPCR検出は有力な補助診断法である．本菌はP3レベルの管理が必要な強い感染性を示すため，通常の病院検査室などでの培養は危険である．
治療と予防
　急性Q熱の多くは予後良好であるが，一部に重症化する例や慢性型への移行もあり得るので，確診例や疑いの強い症例は積極的に治療する．偏性細胞内寄生性の本菌には細胞内移行の不良なβ-ラクタム薬は通常無効であり，移行の良好なテトラサイクリン薬が第一選択である．マクロライド薬やキノロン薬の効果は若干低い．多くは治療開始後数日で解熱するが，ほかの非定型肺炎の場合と同様にいずれの薬剤も2～3週間の投与期間を要する．
　日本ではQ熱に対する認識が浅いためワクチンは普及していない．欧米では家畜用やヒト用のワクチンが実用化されているが，ヒトでのワクチンの適応は，屠畜場や酪農業の従業員，獣医や動物実験施設の従業員などの保菌動物との接触が多い集団に限られる．［渡辺　彰］
■文献
Maurin M, Raoult D：Q fever. Clin Microbiol Rev, 12: 518-553, 1999.
高橋　洋，渡辺　彰：44.Ｑ熱［コクシエラ］(Coxiella burnetii)．病原菌の今日的意味改訂4版（松本慶蔵編）， pp.726-738，医薬ジャーナル社，大阪，2011.

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