If left untreated, the condition may become chronic.

如果得不到治疗，此病可能会转成慢性。

《柯林斯英汉双解大词典》

If left untreated, decay goes deeper and deeper into the tooth.

如果不及时治疗，蛀牙会越来越深。

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If left untreated, visceral leishmaniasis is usually fatal.

如果不及时治疗，内脏利什曼病通常是致命的。

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Lupus can be life threatening if left untreated.

VOA: special.2009.04.14

If left untreated,fistula can cause other health problems.

VOA: special.2010.08.09

If left untreated, sleeping sickness kills.

VOA: special.2010.01.04

In a worst-case scenario, if left untreated, this condition could increase the chance of developing cancer.

FORBES: Magazine Article

Instead, it detects abnormalities which, if left untreated, could lead to cancer in a woman's cervix.

BBC: Cervical screening: Third of Nottingham women miss tests

Hepatitis causes inflammation of the liver and can lead to serious illness and death if left untreated.

BBC: New organisation launched to help prevent hepatitis