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Clinical Presentation of West Nile Virus

Clinical Presentation

What are the clinical signs of West Nile virus infection?

The clinical signs of WNV infection vary between species; however, WNV does not always produce illness in animals or people.  Clinical signs according to species are outlined below:

• Dogs and Cats
• Although it is possible for dogs and cats to be exposed to West Nile Virus, the virus does not tend to cause serious illness in these animals.

• Birds – West Nile virus has been reported in more than 150 species of North American birds 

• Illness in birds includes three phases, although birds do not usually show signs of infection until the last stage of the disease:
• Phase I signs include depression, anorexia and drowsy appearance; recovery is likely
• Phase II signs include depression, anorexia, drowsy, greenish diarrhea, central blindness and ataxia; recovery possible with intense therapy
• Phase III signs include seizures, tremors and death 

• Horses – the virus infects the central nervous system and may cause symptoms of encephalitis 

• Muscle fasciculations
• Mentation/behavior changes
• Lethargy
• Loss of appetite
• Weakness (especially of hind limbs) 

• Ataxia
• Paralysis (especially of hind limbs)
• Convulsions
• Circling
• Head pressing 

• Humans
  
• Asymptomatic disease
• Most people infected (approximately four out of five) have no symptoms
• West Nile fever (seen in about 20% of human cases)
• Fever
• Headache
• Tiredness
• Body aches
• Skin rash on trunk of body
• Swollen lymph glands
• Severe disease (Neuroinvasive disease, West Nile encephalitis, meningitis or West Nile poliomyelitis) is seen in about 1 of every 150 human cases

• Headache
• High fever
• Neck stiffness
• Stupor
• Disorientation
• Coma
• Tremors
• Convulsions
• Muscle weakness
• Paralysis

What can you do to prevent West Nile Virus?

A Case of West Nile Encephalitis in a Human:

This author was given a rare opportunity to interview a young woman in Guilford County, N.C. who became infected with West Nile virus in 2007.  Here is her story in her own words:

In July 2007, when I was 17 years old, I traveled to Costa Rica to participate in a tropical ecology course.  I stayed there for three weeks, mostly in the rainforest.  Needless to say, I received a lot mosquito bites during that time.  During the return trip home, I was feeling tired and run down, like I was getting the flu.  The day after I returned home, I developed a high fever, nausea, vomiting, joint pain and really bad headaches.  I was in bed for about five days and was incredibly weak; I felt like I had a brain fog – I couldn’t concentrate and was having trouble remembering things.  By about the fifth day, my fever had reached nearly 105 degrees and my mother took me to the emergency room at the hospital.  I was having violent chills, hallucinations and I was dehydrated and so weak and my head hurt badly.  I was given IV fluids and anti-inflammatories and they ran a bunch of tests.  My fever came down and they let me go home.  

I continued to have some nausea and vomiting for about two more days, and weakness, terrible joint pain and that “brain fog” for about two more weeks.  I had followed up with my regular doctor shortly after my ER visit and he drew more blood for testing.  After about two more weeks passed, I began feeling better.  Around the same time I was feeling better, my doctor called and said, “You have West Nile virus.”  

The end result of my infection with this virus is that I was not allowed to give blood for five years, which was okay with me because I developed a terrible phobia of needles.  I think the phobia comes from the hallucinations I was having in the emergency room coupled with the multiple needle sticks I had to endure since I was so dehydrated and they had such a hard time finding a vein.  I still have occasional random joint pains, which may be related to the viral infection.   T.S.

Thank you to “T.S.” for sharing her story with me.  I have first-hand knowledge that she suffered cruelly when she was ill with West Nile virus.  She is now 23 years old and employed as an Environmental Specialist with the North Carolina Department of Environment and Natural Resources. 

References: 

Centers for Disease Control and Prevention, (2012). West nile virus; Symptoms of west nile virus. Retrieved from website: http://www.cdc.gov.

Subbiah, E. Equine Viruses Class Notes.  VM8124. 2013.

Pennsylvania’s West Nile Virus Control Program, (2013). What horse owners should know about west nile virus.  Retrieved from website:  http://www.westnile.state.pa.us/animals/horses.htm.

West Nile Virus, (2012). West nile virus symptoms in birds. Retrieved from website: http://www.west-nile-virus-prevention.com/article-west-nile-virus-birds.html.

Images:  

http://www.countrysidemag.com/issues/96/96-1/west_nile_virus_in_horses.html

http://www.cdc.gov

http://www.blogs.equisearch.com

http://wobm.com/west-nile-virus-found-in-three-more-birds/

http://stayhealthla.org

http://www.vdh.state.va.us

West Nile Virus Overview

·      What is West Nile Virus?

o   West Nile Virus is a virus of the family Flaviviridae, specifically of the genus Flavivirus Japanese Encephalitis Antigenic Complex.  Flaviviruses are about 40-60nm in size, enveloped and contain positive-sense single stranded RNA.

·      Where does West Nile Virus occur?

o   West Nile virus exists in Europe, Africa, the Middle East, west and central Oceania.  West Nile Virus was first documented in the United States in 1999 and since then, cases of West Nile Virus have been documented in every state except Oregon, Hawaii, and Alaska.

 

West Nile virus (WNV) activity reported to ArboNET, by state, United States, 2012 (as of December 11, 2012)

http://www.cdc.gov/ncidod/dvbid/westnile/Mapsactivity/surv&control12MapsAnybyState.htm

·      How is West Nile Virus transmitted?

o   There are at least 64 different species of mosquitos that can carry West Nile Virus.  Birds serve as the reservoir host for West Nile Virus, which is then amplified by adult mosquitos following blood feeding.  Mosquitos serve as the primary vector for transmission of West Nile Virus and carry the virus particles in their salivary glands.  When a mosquito feeds on a bird, the virus is transmitted to the bird where it causes an infectious viremia for 1-4 days.  After the viremia subsides in the bird, it develops life-long immunity.  Among bird species, geese have been documented as the only natural host of West Nile Virus, but house sparrows are noted as the most important reservoir host given the high quantity of virus they carry once infected and since they do not die from the viral infection like some other bird species.

There are a very small number of reported cases of West Nile Virus transmission through blood transfusion, transplants, nursing, and pregnancies.

        http://www.cdc.gov/ncidod/dvbid/westnile/cycle.htm

·      Who gets West Nile Virus?

o   West Nile Virus has been detected in more than 326 species of birds.  Some birds, mainly crows and jays, will die from West Nile Virus, but most birds do survive. People, horses, and most other mammals are known to be dead-end hosts for West Nile Virus, meaning they can contract the disease if bitten by an infected mosquito.  Serious disease has not been reported in dogs and cats, but could be possible if the virus is transmitted from an infected mosquito.  Horses are one of the most highly publicized victims of West Nile Virus, with about 40% of infections in horses resulting in death.

Humans can also contract West Nile Virus from infectious mosquito bites.  In 2012, a total of 5,387 cases were reported with 283 deaths.  Individuals over the age of 50 are at increased risk for severe disease.

Infections in chipmunks, bats, squirrels, skunks, llamas, and rabbits have also been reported infrequently.

·      What are the clinical signs of West Nile Virus?

o   Clinical signs of West Nile Virus vary with species affected, but the virus can cause very serious illness and death.  Please see section on Clinical Presentation for more information.

·      How can people get West Nile Virus?

o   There is no evidence that humans can contract West Nile Virus from handling dead or infected birds, but precautions such as avoiding direct contact with bare hands should still be employed.  There is also no evidence of direct human to human transmission or animal to human transmission of West Nile Virus, though blood transfusion/organ transplants and mother to child transmissions have been reported rarely.  The mosquito vector is therefore required to obtain most active West Nile Virus infections.

·      How is West Nile Virus diagnosed?

o   Clinical signs of West Nile Virus allow for presumptive diagnosis.  Collection of whole blood of suspected animals during acute and convalescent stages of the disease and demonstration of a substantial increase in antibody titers is best for definitive diagnosis of the disease.  Virus isolation, serology, Real-Time PCR are all methods of diagnosis applicable to West Nile Virus.

·      How do you treat West Nile Virus?

o   Supportive care for clinical signs and fluid losses are the main treatments of choice.  Virus-specific treatments do not exist for West Nile Virus, so prevention is crucial.

·      How do you prevent West Nile Virus?

o   Mosquito control and the prevention of mosquito bites is the best means to prevent West Nile Virus infection.  Avoiding outdoor exposures during dawn and dusk when mosquitos are most active, using insect repellent/protective clothing, and eliminating common mosquito breeding areas involving standing water are all valid means of decreasing mosquito exposure.

Vaccination for West Nile Virus in horses in the United States is considered by the AAEP as a core viral vaccine and should be used in all horses.  A DNA vaccine is licensed for use in horses as well as a canary poxvirus recombinant vaccine. Regular vaccination of horses is recommended, but should still be employed with appropriate mosquito control protocols.

There are currently no West Nile Virus vaccines for humans, but a vaccine may become available in the future.

·      What is being done to monitor West Nile Virus in the United States?

o   Any horse that develops CNS signs with suspicion of West Nile Virus should be quarantined and appropriate state veterinary officials should be notified.

Federal and State government agencies as well as field veterinarians and physicians monitor and report any cases of West Nile Virus (in any species) to information databases.  The CDC alone has an active surveillance program that provides weekly updates on reported West Nile Virus cases in all species.

REFERENCES

Centers for Disease Control and Prevention, (2012). West nile virus. Retrieved from website: http://www.cdc.gov/ncidod/dvbid/westnile/wnv_factsheet.htm

Subbiah, E. VM 8124 Course Notes, Equine Viruses I. Spring 2013; Lecture 13.

West Nile Virus Crossword

Think you know a lot about West Nile Virus? Try solving this crossword puzzle! A printable version is available here along with the solution to the puzzle. Enjoy!

References:

• Trevejo, Rosalie T., and Millicent Edson. "Vet Med Today: Zoonosis Update- West Nile Virus." JAVMA, Vol 232 No. 9 (2008). <https://www.avma.org/News/Journals/Collections/Documents/javma_232_9_1302.pdf>
• Subbiah, E. Equine Virus Class Notes. VM8124. 2013.

Madison Keller