Symptoms of anthrax infection include a high temperature, chills, a severe headache or breathing difficulties, the HPA said.

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Migraine with aura is a severe headache preceded by symptoms such as seeing flashing lights, temporary visual loss, speech problems or numbness of the face.

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Her record label said Miss Harvey, 31, had complained of a severe headache shortly after returning to Nigeria from the US where she had attended the music industry's Grammy Awards.

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It adds that as universities funding is likely to be cut further in the Comprehensive Spending Review, this would leave the government with a "severe headache about how to plug the gap in the meantime".

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It is estimated that more than a billion pounds is lost every year to the UK economy due to people taking time off work with severe headache or migraine.

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If someone received a less severe exposure, such as through eating, the person would show early symptoms of weakness, confusion, headache, dizziness and shortness of breath.

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