In males, severe febrile illnesses are a known risk factor for non-obstructive azoospermia. After an episode of high fever, temporary reduction of spermiogenesis or complete absence of sperm in the ejaculate may occur. This leads to reversible infertility, which may persist for about two months. The azoospermia is caused by a disruption of the spermiogenesis without a physical obstruction in the genital tract, and is therefore called non-obstructive azoospermia.
In most cases, the sperm count eventually returns back to normal and fertility is restored.
In females, severe fever may also have an adverse effect on fertility and may lead to spontaneous abortion. However, the impact of febrile illnesses on female fertility is not so clearly documented.