Attempts to control a deadly outbreak of dengue fever in northern India that has killed more than 110 people are being hampered by a lack of understanding of which strain of the disease is dominant, doctors are warning.

There are four strains of dengue fever - known as “breakbone fever” as it can lead to severe joint pain and stiffness - with varying degrees of mortality.

The Indian Council of Medical Research (ICMR), the country's leading public health body, has said this outbreak is driven by the D2 strain, which is the most likely to lead to fatal haemorrhaging.

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