The viruses of the bunyavirus family have long presented a challenge to taxonomists and medical doctors alike.  The Hantavirus genus, distinct because it is not transmitted via an arthropod vector,  and the Bunyavirus, Nairovirus, and Phlebovirus genera, collectively grouped because they are transmitted via an arthropod vector, have presented an infectious threat to humans throughout time.  The ecology of the bunyavirus family viruses has a significant effect on the understanding of the disease transmission and epidemiology.  Due to the nature of how each disease tends to be endemic to a particular region with its specific virus, reservoir, and vector, the general population of the region is typically exposed throughout life to the virus.  This has been of significance during wars--the Napoleonic Wars, World War 2, and the Korean War--when non-native troops enter areas without previous exposure to the native viruses.  Hantaan Virus killed nearly 10% of the United Nations soldiers it infected in Korea in 1951;  sandfly fever viruses caused epidemics in the Allied troops in W.W.II and the soldiers of the Napoleonic wars.  More recently the Hantaviruses associated with rodents have become the focus of attention.  In 1993, the Sin Nombre virus associated with the Four Corner's disease was identified in the southwestern region of the United States.  Due to their different mode of transmission and the resulting low level of exposure to even indigenous people, hantaviruses are cause disease in people who become exposed to the virus at high enough concentrations.

Rift Valley Fever
 
Rift Valley fever had been known for many years as a disease of ruminants in East or South Aftrica.  It would break out about once a decade, killing lambs and calves and causing abortion in ewes and cows.  At these times, a dengue-like illness was observed in animal handlers.  In 1977, an major animal outbreak occured in the delta and valley of the Nile.  This was the first time many humans were affected.  Ina 1978 outbreak, over 200,000 Egyptians fell ill and over 600 died.  The next spurt of virus activity was observed in eastern Africa and in western Africa, which left hundreds of humans dead in Mauritania and Senegal. There is currently an outbreak of Rift Valley Fever in Kenya and Somalia.
 

California Encephalitis Virus

California Encephalitis Virus was isolated in 1943 by Reeves and Hammond in Kern County, California.  Since then, related strains of viruses causing encephalitis have been isolated.  For instance, in 1960, La Crosse virus was isolated from a fatal case of encephalitis in La Crosse, Wisconsin.

Bunyamwera Serogroup Viruses

Bunyamwera virus was first isolated in central Africa from mosquitos.  These viruses have not caused epidemics or epizootics.

Hantaan Virus--Hemorrhagic Fever with Renal Syndrome

In 1951, there was an epidemic of hemorrhagic fever among United Nations soldiers in Korea.  This was later called HFRS (Hemorrhagic Fever with Renal Syndrome).  Similar diseases were observed in the former Soviet Union, Manchuria, and China.  Circumstantial evidence suggested that the infection was contracted from wild rodents and their parasites.  The agent was identified by the demonstration of immunofluorescent antigen in the lungs of the field mouse, using sera from patients with Korean hemorrhagic fever.

Sin Nombre Virus--Hantavirus Pulmonary Syndrome

This disease was reported from the Four Corners Region of the southwestern U.S. in May of 1993.  Most cases were in healthy young adults and progressed to death in a matter of days.  See useful links for many web sites containing information about HPS.  It was discovered that the virus was spread by rodents.

Crimean-Congo Hemorrhagic Fever

This virus was isolated first in Africa and later independently in the former Soviet Union.  After World War II, hemorrhagic fever was observed in agricultural workers in the Crimean Peninsula.  It was associaated with the bites of Ixodid ticks.  During the 1960s, a virus causing severe febrile disease was isolated from patients in Zaire and Uganda.  This was subsequently shown to be identical to the Crimean hemorrhagic fever virus.