WNV Preventing

Preventing West Nile Virus in Horses & Horse Owners: 

Preventing West Nile Virus in Horses & Horse Owners Dr. Douglass E. Stevenson, Ph.D. Extension Associate

West Nile Virus (WNV): 

West Nile Virus (WNV) WNV is a member of the flavivirus family of the Japanese Encephalitis virus serocomplex WNV may cause severe encephalitis (brain or spinal cord disease) in humans, horses and birds, particularly crows and blue jays

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West Nile Virus (WNV) normally circulates between wild birds and mosquitoes Humans can also get the virus. Horses are particularly susceptible. People and horses do not pass on the virus.

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WNV Bird Reservoir Birds are the reservoir - the animal species in which the virus is maintained Greater than 80 species of birds have been found infected in North America Members of the Corvid spp (crows and blue jays) are unusually susceptible to illness and frequently die from the disease.

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Avian Reservoir

WNV: 

WNV WNV is transmitted by mosquitoes, the primary species being Culex pipiens (Northern House Mosquito) WNV has been detected in >20 species of mosquitoes in North America Therefore, protection against mosquito bites is very important

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Mosquitoes Infected with WNV Culex Aedes Pipiens Restuans Salinarius Aegypti Albopictus Cantator Japonicus Triseriatus Vexans Bird Feeders Mammal Feeders

The Southern House MosquitoCulex pipiens quinquefasciatus: 

The Southern House Mosquito Culex pipiens quinquefasciatus Female mosquito with raft of eggs Up to 500 eggs/raft

WNV: 

WNV 1st equine outbreak 1962-65 in France Also 1963 in Egypt, Morocco in 1996, Israel and Italy in 1998 Morocco – 42/94 = 44.7% of horse cases died Italy – 6/14=42.9% of horse cases died

WNV in US: 

WNV in US 1999 - 25 equine cases/9 deaths; 9/25=36% 2000 – 60 equine cases/23 deaths; 23/60=38% 2001 – 731 equine cases/71 deaths so far; 71/295=24.1% as of 12/08/01 2002 – 202 confirmed cases in Texas

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WNV in US 2001 Outbreak 28 states & DC 66 humans with 9 fatalities 731 horses in 19 states 7,338 birds all states & DC 918 mosquito pools in 15 states & DC

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WNV in Horses

Common Clinical Signs: 

Common Clinical Signs Ataxia (incoordination)– 85% of cases Depression or apprehension – 50% of cases Weakness – 48% of cases Recumbency (down) – 45% of cases Muscle fasciculations – (neck & body) 40% of cases Fever – 23% of cases Paralyzed or droopy lip – 18% of cases Twitching muzzle – 13% of cases Teeth grinding – 7% of cases Blindness – 5% of cases

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Other Similar Diseases Rabies Ascending paralysis ( from rear to front) Botulism Severe muscle shaking (head, trunk, muzzle) Equine Protozoal Myeloencephalitis (EPM) Asymmetric incoordination and weakness

Diagnosis: 

Diagnosis Diagnosis may be made using serum or cerebrospinal fluid Samples should be sent to Ohio Department of Agriculture Diagnostic Lab Post mortems should not be done in the field, but should be done at the ODA Lab as well

WNV Treatment: 

WNV Treatment Supportive only – fluids, anti-inflammatory medications, nutrients, sling No antiviral medications are available at this time

Can my horse infect me?: 

Can my horse infect me? No, not likely, as the level of virus in the blood is too low. 3 studies have been attempted with 16 horses >600 naïve mosquitoes were fed on 7 infected horses. None of the mosquitoes became infected Since we don’t know about severely affected horses, caution should always be taken.

WNV Prevention: 

WNV Prevention There is currently a vaccination available for horses Horses should receive 2 initial doses, 3 to 6 weeks apart Second dose no later than April 15th If vaccinated early in year, should receive a booster in July

Vaccine Efficacy: 

Vaccine Efficacy Unknown at this time In the same serocomplex as Japanese Encephalitis (JE) virus JE vaccine has proven very effective in horses and people Therefore, it is expected the current WNV vaccine will be effective

WNV Prevention: 

WNV Prevention No vaccine is 100% effective, therefore mosquito control is necessary both for the horses and their owners Reducing the sources for mosquito breeding both around your house and other areas around your farm and personal protection will help to reduce the risk for WNV infection

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Most horse facilities have multiple mosquito breeding areas!

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Stagnant pools should be drained or larvicide's should be used WNV Prevention

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Mosquito dunks are non-toxic, biological mosquito control May be safely used in horse water troughs WNV Prevention

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Mosquito magnet Offers coverage up to 1 acre Attracts the mosquitoes and then dries them up Expensive WNV Prevention

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Remove old tires as mosquitoes love to breed in them If you must keep them, cut them in half or treat them WNV Prevention

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Whole tires should not be used on silos WNV Prevention

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Split tires are much safer for mosquito reduction WNV Prevention

WNV Prevention: 

WNV Prevention Old equipment where stagnant water may accumulate should be emptied, turned over or removed

WNV Prevention: 

WNV Prevention Old tubs or water troughs not in use should be turned over or trashed

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Keep vegetation down at the edge of ponds or lagoons WNV Prevention

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Ponds and lagoons should be kept free of debris WNV Prevention

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Keep horses inside during high mosquito activity Lights off at night Use fans Put incandescent lights on outside of farm property WNV Prevention

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Keep all birds away from the barn Remove any potential reservoir www.birdbgone.com WNV Prevention

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For information regarding this slide presentation, please contact: Dr. Douglass E. Stevenson Extension Associate Texas Cooperative Extension d-stevenson@tamu.edu 115-A Agronomy Field Laboratory Texas A&M University College Station TX 77843-2488