3West Nile VirusOne of several mosquito-borne viruses in the United States that can infect peopleThe virus exists in nature primarily through a transmission cycle involving mosquitoes and birds.Mosquitoes become infected with West Nile virus (WNV) when they feed on infected birds
4West Nile Virus Symptoms Majority of people that become infected with the West Nile virus have no illness or experience only a mild flu-like illnessMay include fever, headache and body aches lasting only a few daysSome persons may also have a mild rash or swollen lymph glandsLess than one percent of those infected may develop meningitis or encephalitis, the most severe forms of the disease
5How Long has the West Nile Virus Been Around? Alexander the Great, 336 B.C., conquered a vast empireIt’s speculated that his demise was due to West Nile encephalitisThere is still no human vaccine for West Nile virus
6West Nile Virus Takes Off West Nile Virus is pathogenic, it invades its host and multiplies, causing diseaseIt’s a flavivirus, traveling inside mosquitoes which act as the transferring agent from host to host
76Viral Multiplication - Basic Steps Attach to host cellEnter host (virus or just genetic material)Direct host to make viral genetic material and proteinAssemble viral nucleic acids and proteinsRelease new viral particles
78e Lysis of host cell is induced; infectious particles escape. Lytic Pathwayd The coats get tail fibers, other parts.LyticPathwaya Virus particle injects genetic material into a suitable host cell after binding to its wall.c Viral proteins are assembled into coats around viral DNA.b Viral DNA directs host cell to make viral proteins and replicate viral DNA.a-1 Viral DNA is integrated into the host’s chromosome.a-4 Viral DNA is excised from the chromosome.LysogenicPathwaya-2 Before prokaryotic fission, the bacterial chromosome with the integrated viral DNA is replicated.a-3 After cell division, each daughter cell will have recombinant DNA.Fig , p.344
80Lysis of host cell is induced; infectious particles escape. Lytic PathwayTail fibers and other parts are added to coats.Virus particles bind to wall of suitable host. Viral genetic material enters cell cytoplasm.Viral protein molecules are assembled into coats; DNA is packaged inside.Viral DNA directs host machinery to produce viral proteins and viral DNA.
82Viral DNA usually becomes integrated into the bacterial chromosome. Lysogenic PathwayViral DNA is excised from chromosome and cell enters lytic pathway.Prior to prokaryotic fission, the chromosome and integrated viral DNA are replicated.After binary fission, each daughter cell will have recombinant DNA.
86Replication of an Enveloped Virus Enveloped DNA virus replication
87Nature of DiseaseContagious disease pathogens must directly contact a new hostEpidemicPandemic (AIDS)SporadicEndemic
88Evolution and Disease Host and pathogen are coevolving If a pathogen kills too quickly, it might disappear along with the individual hostMost dangerous if pathogenIs overwhelming in numbersIs in a novel hostIs a mutant strain