Mydriasis is the dilation of the pupil, usually having a non-physiological cause, or sometimes a physiological pupillary response. Non-physiological causes of mydriasis include disease, trauma, or the use of certain types of drugs. Normally, as part of the pupillary light reflex, the pupil dilates in the dark and constricts in the light to respectively improve vividity at night and to protect the retina from sunlight damage during the day. A mydriatic pupil will remain excessively large even in a bright environment. The excitation of the radial fibres of the iris which increases the pupillary aperture is referred to as a mydriasis. More generally, mydriasis also refers to the natural dilation of pupils, for instance in low light conditions or under sympathetic stimulation. Fixed, unilateral mydriasis could be a symptom of raised intracranial pressure. The opposite, constriction of the pupil, is referred to as miosis. Both mydriasis and miosis can be physiological. Anisocoria is the condition of one pupil being more dilated than the other. Causes
There are two types of muscle that control the size of the iris: the iris sphincter, composed of circularly arranged muscle fibers, and the iris dilator, composed of radially arranged muscle fibers. The sphincter is controlled by nerves of the parasympathetic nervous system, and the dilator by the sympathetic nervous system. Sympathetic stimulation of the adrenergic receptors causes the  contraction of the radial muscle and subsequent dilation of the pupil. Conversely, parasympathetic stimulation causes contraction of the circular muscle and constriction of the pupil.
Post infection (and providing that the person survives the infection), those that have contracted BHF are usually immune to further infection of the disease. Weaponization
Bolivian hemorrhagic fever was one of three hemorrhagic fevers and one of more than a dozen agents that the United States researched as potential biological weapons before the nation suspended its biological weapons program in 1969. Albert Nickel, a 53-year old animal caretaker at Fort Detrick, died in 1964 from the disease after being bitten by an infected mouse. Nickel Place, on Fort Detrick, is named in his honor. It was also under research by the Soviet Union, under the Biopreparat bureau. Vaccine research
Investigational vaccines exist for Argentine hemorrhagic fever and RVF; however, neither is approved by FDA or commonly available in the United States.The structure of the attachment glycoprotein has been determined by X-ray crystallography and this glycoprotein is likely to be an essential component of any successful vaccine. References
Bibliography

Medical Microbiology 2nd Edition Mims et al. Mosby Publishing 1998 p 371


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