Erythema infectiosum (Fifth disease)

Japanese: 伝染性紅斑（リンゴ病） - でんせんせいこうはん（リンゴびょう）（英語表記）Erythema infectiosum (Fifth disease)

What kind of infection is it?

Erythema infectiosum is also known as "apple disease" because the cheeks turn red like an apple. It most commonly occurs in children between the ages of 5 and 9.

The cause is infection with the B19 virus, which belongs to the genus Erythrovirus and belongs to the Parvoviridae family. It infects the P antigen on the membrane surface of red blood cells, and mainly Erythroid precursors ( Cough flu ) They infect cells and multiply.

How symptoms manifest

After an incubation period of 10 to 20 days, children usually develop an apple-red cheek, followed by a lacy rash on the hands and feet. The rash may reappear. In adults, the cheek rash is often absent, but the rash on the hands and feet and the whole body may appear. Fatigue ( Health test ) Or there may be only arthritis symptoms, rubella ( Newspaper ) It is often mistaken for.

It usually heals naturally within a few days. By the time the rash appears, the infection is no longer contagious, and it is said that the infection is most contagious about one week before the rash appears.

If a pregnant woman becomes infected, the fetus can become infected, causing severe anemia, fetal death, miscarriage, and fetal hydrops, so caution is required. Also, if a patient with chronic anemia becomes infected, it can cause severe symptoms.

Testing and diagnosis

In most cases, children are usually diagnosed based on typical clinical symptoms, but in adults, it is difficult to distinguish it from rubella without virological testing. Diagnosis is made by detecting the viral gene (DNA) in serum using the PCR method, by checking the positive or increase in IgG antibodies in blood samples taken during the acute and convalescent phases, or by detecting specific IgM antibodies during the acute phase.

Treatment methods

Usually, only symptomatic treatment is available. By the time symptoms appear, the disease is already almost non-infectious, making it difficult to prevent infection. There is no vaccine. In immunocompromised patients or those with chronic anemia, Gamma ( gamma ) Globulin preparations may be administered. If a pregnant woman is infected, there is a 20-30% chance that the fetus will be infected, so fetal monitoring is necessary.

What to do if you notice an illness

Since the virus is not contagious when symptoms appear, it is not a disease that requires schools, kindergartens, or daycare centers to suspend attendance. However, people with underlying conditions and pregnant women should visit their pediatrician, internist, or obstetrician-gynecologist and discuss the matter thoroughly.

Kaoruko Taya

Erythema infectiosum (fifth disease)
Electrical stimulant (apple paste)
Erythema infectiosum (Fifth disease)
(Childhood illnesses)

What is the disease?

It is an acute viral disease of school-age children characterized by the appearance of red spots (that look like an apple) on both cheeks.

What is the cause?

It is caused by a small virus called human parvovirus B19. It is most common in school-age children (6-12 years old), and occurs in epidemics in facilities and schools from winter to spring. It is said to be transmitted through the respiratory tract, and is not contagious once the rash appears.

How symptoms manifest

After an incubation period of 16 to 17 days, red spots appear on the cheeks. Maculopapular rash ( Consolidation ) The rash merges and both cheeks become slap-like, apple-like, diffuse (widespread) erythema, resembling a butterfly with its wings spread (Figure 49). After 1-2 days, erythema appears on the upper limbs and thighs, and the center of the rash fades, forming a marbled, lace-like, or map-like rash. The rash is itchy and may reappear when exposed to sunlight or heat. It will heal in 2-3 weeks.

In children with chronic hemolytic anemia, Bone marrow aplastic crisis ( Kotsu-zumu Keisei Hossa ) If a pregnant woman is infected, the fetus may become infected and Hydrops fetalis ( Taijisuishu ) This can make it difficult to continue the pregnancy.

Testing and diagnosis

The number of peripheral blood white blood cells tends to decrease, and reticulocytes also decrease and disappear. Diagnosis is usually not difficult if there is evidence of an epidemic, a high number of infections among school children, and butterfly rash on the face, and no testing is required. Erythema multiforme ( Takeuchi Shinshuu Kouhan ) It may be necessary to distinguish it from maculopapular diseases such as urticaria and drug rash.

Treatment methods

There is no specific cure for this virus, and although symptomatic treatment is given as needed, the prognosis is good.

What to do if you notice an illness

When the rash appears, the virus is not being excreted and the child is not contagious, but it is best to wait until the rash has disappeared before returning to school. There is no method of prevention.

Kizo Asano

Figure 49. Erythema infectiosum
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Figure 49. Erythema infectiosum

Source: Houken “Sixth Edition Family Medicine Encyclopedia” Information about the Sixth Edition Family Medicine Encyclopedia

Japanese:

どんな感染症か

　伝染性紅斑は頬がリンゴのように赤くなることから、通称「リンゴ病」とも呼ばれています。5～9歳ごろに最も多く発症します。

　原因はパルボウイルス科エリスロウイルス属に属するB19ウイルスの感染です。赤血球の膜表面にあるP抗原を受容体として感染し、主に赤芽球前駆(せきがきゅうぜんく)細胞に感染して増殖します。

症状の現れ方

　10～20日の潜伏期ののち、子どもでは通常、頬がリンゴのように真っ赤になり、その後手足にレース状の発疹が現れます。いったん消えた発疹が再び現れることもあります。成人では頬の紅斑を認めないことが多く、手足の発疹、全身倦怠感(けんたいかん)や関節炎症状だけの場合があり、風疹(ふうしん)と間違われることが多くあります。

　通常数日の経過で自然に治ります。発疹が現れるころにはもう感染力はほとんどなく、発疹出現前1週間くらいの感染力がいちばん高いといわれています。

　妊婦が感染すると胎児に感染し、重度の貧血から胎児死亡、流早産、胎児水腫(すいしゅ)を起こすことがあるため注意が必要です。また、慢性貧血の患者さんがかかると、重い症状を起こすことがあります。

検査と診断

　通常、小児では典型的な臨床症状から診断されることがほとんどですが、成人の場合、ウイルス学的な検査をしないと風疹との区別が困難です。血清中のウイルス遺伝子（DNA）をPCR法で検出したり、急性期と回復期に採血してIgG抗体の陽転あるいは上昇を確認したり、急性期の特異的IgM抗体を検出することで診断します。

治療の方法

　通常は対症療法のみです。症状が現れた時はすでに感染力がほとんどないため、感染予防が困難な病気です。ワクチンもありません。免疫不全の患者さんや慢性貧血のある患者さんでは、発症時にγ(ガンマ)グロブリン製剤が投与されることがあります。妊婦が感染すると、20～30％の割合で胎児に感染するといわれており、胎児の経過観察が必要になります。

病気に気づいたらどうする

　症状が出た時にはほとんど感染力はないので、学校、幼稚園、保育所では登校・登園停止の疾患にはなっていません。ただし、基礎疾患がある人、妊婦などは、かかりつけの小児科、内科、産婦人科を受診し、よく相談する必要があります。

多屋　馨子

伝染性紅斑（リンゴ病）
でんせんせいこうはん（リンゴびょう）
Erythema infectiosum (Fifth disease)
(子どもの病気)

どんな病気か

　両方の頬に紅斑（リンゴのようにみえる）ができることを特徴とする学童期の急性ウイルス性疾患です。

原因は何か

　ヒトパルボウイルスB19という小さなウイルスが原因です。学童期（6～12歳）にかかることが多く、冬から春にかけて、施設、学校で流行性に発生します。経気道感染といわれ、発疹が現れた時には伝染力はないといわれています。

症状の現れ方

　16～17日の潜伏期のあと、頬部に紅い斑状丘疹(はんじょうきゅうしん)が現れます。発疹は融合し、両頬は平手打ち様、リンゴ様のびまん性（広がりのある）紅斑になり、ちょうど蝶が羽を広げたように見えます（図49）。1～2日後から上肢、大腿の順に紅斑が現れ、発疹の中央が退色して大理石紋様、レースのような編み目状あるいは地図状皮疹になります。発疹はかゆみを伴い、日光、温熱により再び現れることがあります。2～3週の経過で治ります。

　慢性溶血性(ようけつせい)貧血の患児では、本症により骨髄無形成発作(こつずいむけいせいほっさ)を起こすことがあります。妊婦がかかった場合では、胎児が感染し、胎児水腫(たいじすいしゅ)を起こして妊娠の継続が困難になることがあります。