Eastern Equine Encephalitis Virus Biology Essay

On August 13, 2010, public wellness functionaries in Southwest Michigan informed community members that a 3rd individual had contracted an infection from Eastern Equine Encephalitis Virus. Before the terminal of the summer, one more individual would go septic, conveying the one-year sum in that little corner of the province to four ( Emerging Disease Issues ) . Though four instances does non do for an epidemic, this sudden addition in prevalence had wellness functionaries concerned, particularly sing the mean one-year figure of instances of human EEEV infections in the United States is six ( Centers for Disease Control ) , and that since 1964 there have merely been 13 confirmed instances in the full province of Michigan ( Centers for Disease Control ) . In an attempt to appreciate the earnestness of this somewhat vague virus as an infective agent in Michigan, this paper will look at the morphology and “ lifestyle ” of EEEV, and will discourse at length the disease it causes and its impact on public wellness. The position of current research and chances for future research into EEEV will besides be discussed.

Structure and Categorization

Public wellness functionaries have long been cognizant of EEEV and the hazard it poses to both Equus caballuss and people. It was foremost isolated in Equus caballuss in 1933, and in worlds in 1938 ( Aguilar et al. , 4920 ) . It is a member of the household Togaviridae and the genus Alphavirus ( Centers for Disease Control ) . There are four subtypes of EEEV based on antigenic differences between strains ( Arrigo et al. , 1014 ) . Subtype I includes all North American and Caribbean strains, while subtypes II, III, and IV include strains from South and Central America ( Arrigo et al. , 1014 ) .

The subtypes of EEEV vary at the nucleotide degree by every bit much as 38 % . Interestingly, the North American subtype is known to do disease in worlds while the South American strains do non ( Arrigo et al. , 1015 ) .EEEV is an enveloped virus with an icosahedral mirid bug, and possesses a non-segmented, single-stranded RNA genome, doing it a member of the Baltimore categorization IV ( Aguilar et al. , 4920 ) . The genome is about 11.7 kilabases in size and is of a positive sense, intending it can work straight as an messenger RNA transcript and be read from 5 ‘ to 3 ‘ by the host cell ribosome during interlingual rendition ( Aguilar et al.

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, 4920 ) .Similar to other Alphaviruses, EEEV reproduction occurs in the cytol of septic cells. The genome has both a 5 ‘ Cap and a poly ( A ) tail that map to enroll the cell ribosome for interlingual rendition and to forestall debasement, severally ( Arrigo et al. , 1014 ) . Like other positive sense RNA viruses, interlingual rendition of the two unfastened reading frames of the EEEV genome consequences in the formation of a big polypeptide that is subsequently cleaved into smaller protein units ( Aguilar et al. , 4920 ) .

The genome encodes three major structural proteins, the mirid bug and two envelope proteins ( Aguilar et al. , 4920 ) . The envelope proteins, E1 and E2, are rather various and are involved in host cell receptor acknowledgment and binding to these receptors during fond regard ( Aguilar et al. , 4920 ) . They are besides the cardinal proteins involved in incursion and membrane merger during entry into the host cell ( Aguilar et al.

, 4922 ) . Additionally, the envelope proteins interact with the mirid bug during viral assembly and release of atoms ( Aguilar et al. , 4923 ) . The EEEV genome besides encodes four non-structural proteins, including a peptidase, that are used for viral reproduction, RNA, and polypeptide processing ( Aguilar et al. , 4920 ) .


EEEV is endemic to North America, where its natural reservoir is wild birds ( Schmitt et al. , 636 ) . The avian hosts of EEEV typically reside in fresh water hardwood swamps ( Centers for Disease Control ) .

EEEV is considered an arborvirus, an acronym standing for arthropod-born virus ( Centers for Disease Control ) . Transmission from bird to bird is typically carried out by the mosquito Culiseta melanura, a species of mosquito that feeds about entirely on birds ( Centers for Disease Control ) . Transmission of EEEV to non-bird species, including worlds, nevertheless, is normally carried out by mosquito species of the genera Coquillettidia and Aedes ( Michigan Department of Natural Resources and Environment ) . These mosquitoes function as span vectors, reassigning the virus from septic birds to clean mammals, reptilians, and amphibious vehicles ( Schmitt et al. , 635 ) . Animals besides birds are said to be “ dead-end hosts ” because they can non go through the infection on to other animate beings and do non go around adequate virus in their blood to go through the infection on through mosquitoes ( Centers for Disease Control ) .


Once in the organic structure, EEEV travels via lymphatic canals to lymph nodes where it replicates in neutrophils and macrophages ( Cooper and Scott, 1405 ) .

Following an incubation period of between four and ten yearss, these cells begin to exhibit cytopathic effects. Cells become shriveled and show elongated cytoplasmatic borders ( Vogel et al. , 163 ) . At this phase of infection, the host innate immune response is typically activated as evidenced by the release of interferons from host lymph cells ( Vogel et al. , 162 ) . The EEEV infection can either be cleared from the organic structure or consequence in disease, viz.

phrenitis ( swelling of the encephalon ) or systemic viraemia ( Centers for Disease Control ) . The type of unwellness contracted depends on a assortment of host factors including age and immune system wellness ( Centers for Disease Control ) .Systemic viraemia infection typically lasts one to two hebdomads and is characterized by febrility, icinesss, lassitude, and myodynia ( Roy et al. ) . Provided there is no engagement with the cardinal nervous system, recovery from systemic EEEV infection is normally complete.

The encephalitic signifier of the disease ( Eastern Equine Encephalitis, or EEE ) normally arises after one to several yearss of systemic infection, except in babies where marks of phrenitis appear quickly ( Vogel et al. 162 ) . Symptoms of phrenitis include fever above 103-degrees Fahrenheit, concern, purging, diarrhoea, a stiff cervix and back, anorexia, paroxysms, and coma ( Centers for Disease Control ) .


The Centers for Disease Control study that about tierce of people who contract an encephalitic infection from EEEV dice from the disease. Of those who recover, many are left with enfeebling chronic mental and physical jobs such as ictuss, rational damage, nervus disfunction, and personality upsets ( Centers for Disease Control ) . The disease is even more lifelessly in Equus caballus populations, where it kills between 75 and 90 per centum of the animate beings it infects ( Schmitt et al. , 637 ) .The high human death rate makes EEE one of the most unsafe mosquito-born diseases in North America, and to day of the month there is no remedy.

The disease does non typically react to aciclovir or other normally used antiviral drugs ( Centers for Disease Control ) . Symptoms are treated with antiepileptics and anti-inflammatory medicines such as corticoids ( Centers for Disease Control ) . Other steps are taken to supply supportive attention for patients, including disposal of endovenous fluids and antipyretic drugs ( febrility reducing agents ) , and tracheal cannulation ( Centers for Disease Control ) . In Equus caballuss, the antiviral drug Ribavirin has been used to handle encephalitic unwellness with some modest success ( Michigan Department of Natural Resources and Environment ) .


As antecedently stated, EEEV is transmitted to worlds merely through the bite of an septic mosquito. Because the natural reservoir for EEEV is wild birds, this virus ‘s primary transmittal rhythm is rural in nature, happening chiefly in barely populated hardwood swampy countries ( Michigan Department of Natural Resources and Environment ) . Consequently, infections in worlds are comparatively rare.

Since 1964, an norm of merely six instances of human EEEV infection have been reported yearly in the United States ( Centers for Disease Control ) . People life and working in rural countries are at highest hazard of infection, though merely about 4 % of human EEEV infections really result in Eastern Equine Encephalitis, and the bulk of those occur in people older than 50 or younger than 15 ( Centers for Disease Control ) . Those infected by EEEV get life-long unsusceptibility against re-infection, but do non derive unsusceptibility against other encephalitic viruses of the Alphavirus genus such as Venezuelan Equine Encephalitis or Western Equine Encephalitis ( Centers for Disease Control ) .In the United States, most instances of human EEEV infection occur in the southeast provinces of Georgia, Florida, Louisiana, North Carolina, South Carolina, and Mississippi, though infections sporadically occur in provinces in the nor’-east and Great Lakes. Since 1964 when the CDC began maintaining records on EEEV infections, no province West of Texas has reported a human infection ( Centers for Disease Control ) . The virus has an overall geographic distribution that extends north into the Eastern Canadian states of Ontario, Quebec, and New Brunswick, and south into the eastern part of Mexico, through Central America, and as far into South America as Eastern Argentina ( Centers for Disease Control ) .

Current Research

With the coming of the molecular epoch of biological science, much of the current research on Eastern Equine Encephalitis Virus is directed at understanding this pathogen on a little graduated table. Some evolutionary life scientists are utilizing RNA sequence informations to better understand the similarities and differences that exist between the EEEV and other closely related Alphaviruss like Western Equine Encephalitis Virus, Venezuelan Equine Encephalitis Virus, and Sindbis Virus ( Arrigo et al.

, 1016 ) . Besides, a good trade of current research is focused on understanding the virus-host interactions between EEEV and the many animate beings it can infect, particularly on the bird species that serve as its natural reservoir. Possibly the greatest sum of resources, though, is devoted to disease bar and epidemiological surveies to track eruptions of EEEV in the United States.

Potential for Weaponization

Though many infective viruses are considered as possible agents of biological warfare, few possess as many of the features necessary for successful weaponization as the Alphaviruses ( Croddy and Wirtz, 125 ) . In fact, the former Soviet Union reportedly had a big reserve of weaponized EEEV ( Croddy and Wirtz, 126 ) . The United States besides conducted research into the usage of EEEV as a arm before it ratified the Biological Weapons Convention in 1972, seting a halt to all biological warfare activity ( Croddy and Wirtz, 127 ) . The virus can be grown easy in big measures cheaply. Bing a BSL-1 or 2 agent, EEEV is in stock in legion research research labs in the United States and could most probably be attained with comparative easiness.

A recent survey on guinea hogs, the carnal theoretical account of pick for measuring the impact of many aerosolised infections, concluded that EEEV atoms are stable and extremely morbific in aerosol signifier ( Roy et al. , ) . Furthermore, the multiple serotypes of EEEV make the development of effectual defensive vaccinums against it rather hard ( Croddy and Wirtz, 128 ) .

In Michigan

Public wellness functionaries in Michigan have confirmed 130 instances of Eastern Equine Encephalitis in Equus caballuss so far in 2010 ( Michigan Department of Natural Resources and Environment ) . However, it is the four confirmed human instances, the first in Michigan since 2002, which have that province ‘s occupants most concerned ( Emerging Disease Issues ) One possible ground for this addition in prevalence of this disease is the conditions ( Michigan Department of Natural Resources and Environment ) . In 2010, Michigan experienced one of its hottest and wettest summers on record, doing conditions really favourable for mosquito growing and reproduction. Additionally, local veterinaries fear that hapless local economic systems have resulted in less Equus caballuss being vaccinated against the disease. Harmonizing to one appraisal, EEEV inoculation in Michigan Equus caballuss is down by every bit much as 40 % compared to merely ten old ages ago ( Emerging Disease Issues ) . This guess, of class, bears no impact on the figure of human instances, as mammals are dead-end hosts for EEEV. County, State, and Federal wellness functionaries closely monitor all suspected and confirmed instances of EEE in Michigan, and great steps are taken to cut down mosquito populations during peak times of the twelvemonth.


Future research into EEEV will probably maneuver down many roads. Evolutionary life scientists will go on to bring out the molecular relationships between the discrepancies of EEEV and other closely related Alphaviruss. Epidemiologists will go on tracking eruptions of the EEEV disease and local public wellness governments will go on to work to cut down mosquito populations during peak summer months. Virologists and diagnosticians will go on to clarify the mechanisms by which EEEV causes disease in animate beings and worlds, and hopefully bring out the grounds why the immune systems of some are able to unclutter the infection while others develop enfeebling and frequently fatal phrenitis.

The lethality of EEEV infections makes the virus a legitimate public wellness concern. Though the rise in prevalence of human EEE in my place country of Michigan may hold been the consequence of an remarkably hot summer with really high precipitation making conditions optimal for mosquito growing, it besides may hold been a simple statistical anomalousness. We will likely ne’er cognize. What is known, though, is that in the absence of a agency of eliminating this disease, which would intend eliminating the birds who serve as its natural reservoir, continued steps are needed to guarantee close monitoring and prompt response to EEEV eruptions, modest as they may be.


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