viral hemorrhagic fevers are caused by viruses of four distinct families: arenaviruses filoviruses bunyaviruses and flaviviruses. each of these families share a number of features: they are all rna viruses and all are covered or enveloped in a fatty (lipid) coating. their survival is dependent on an animal or insect host called the natural reservoir. the viruses are geographically restricted to the areas where their host species live. humans are not the natural reservoir for any of these viruses. humans are infected when they come into contact with infected hosts. however with some viruses after the accidental transmission from the host humans can transmit the virus to one another. human cases or outbreaks of hemorrhagic fevers caused by these viruses occur sporadically and irregularly. the occurrence of outbreaks cannot be easily predicted. with a few noteworthy exceptions there is no cure or established drug treatment for vhfs. in rare cases other viral and bacterial infections can cause a hemorrhagic fever; scrub typhus is a good example.
how are hemorrhagic fever viruses grouped?