Eastern Equine Encephalitis in Three Alpacas by Amy Bright, DVM

Eastern Equine Encephalitis in 3 Alpacas

Amy Bright, DVM

Fall is supposed to be a quieter time in a mixed animal veterinary practice. Farm visits are generally spent enjoying nature’s colorful show while examing healthy animals ready for the fair season. However, two weeks in late September 2005 brought a whirlwind of sick alpacas, dying of a disease that was not previously on the veterinarian’s radar for camelid species.

When the storm was over the casualties were 3 dead alpaca crias and one yearling alpaca. Three of these animals were diagnosed post mortem with Eastern Equine Encephalitis (EEE). The 4th animal (and first presented case) did not have any postmortem diagnostic tests run, but was also strongly suspected to have succumbed to EEE.

EEE is a virus that is maintained in the wild bird and mosquito populations. It is transmitted by mosquito bites and can cause illness in humans, horses, camelids, as well as other species. Symptoms of the disease are related to the central nervous system malfunction. The virus causes inflammation in the brain and associated tissues that prohibits many normal neurologic functions.

Presentation of these animals to the hospital fell between September 17th and 27th, 2005. On presentation, the neurologic signs of these animals were mild and included: star gazing (staring off into space with head tilted upwards), ataxia (incoordination of limbs), inability to maintain a nursing position, mental dullness, head tilt, and difficulty rising. Three animals were young crias, between 2 and 4 weeks old. One animal was a yearling. Fever was present only intermittently.

The lab work of these animals was inconsistent. They did not have any common values in the serum chemistry, nor did they have similar complete blood counts. Only the yearling exhibited leukopenia (decreased white blood cell count) that is sometimes seen in other species when fighting off viruses.

Various supportive treatments in these animals such as oral nutritional supplementation, antibiotics, vitamin B and selenium supplementation, intravenous fluid therapy, non steroidal anti-inflammatories (Flunixin meglumine), and free radical scavengers (DMSO) did not achieve anything more than mild temporary improvement of neurologic status and fever reduction. All these cases progressed within 6–96 hours to a state in which they were unable to rise and exhibiting seizure activity. The younger animals seemed to progress more quickly. Seizure activity did not respond to treatment with benzodiazepams (anti-convulsant drug). With worsening signs and a grave prognosis for survival the owners elected euthanasia for these animals.

Diagnosis of EEE was confirmed in three cases by Reverse Transcriptase PCR (confirming the presence of viral DNA) in brain tissue samples obtained post mortem. These samples were all negative for West Nile Virus, another mosquito born virus that can cause neurologic signs. We were fortunate to receive the diagnosis on the first case while the other two animals were still in the hospital. This new information allowed us to try new therapies and counsel the owners accordingly.

In the midst of two weeks like the above a veterinarian (and involved breeders) can feel frustrated and helpless. Hoping only for a hard frost before more animals can become infected. However, I feel a lot of good has come from this outbreak.

The most impressive factor I noticed during the outbreak was the open communication between breeding farms. The group of breeders we worked with kept each other informed with medical changes and provided moral support for the farms with affected animals. There were no secrets kept about sick animals even though the cause of the sickness had yet to be determined. The breeders had an increased awareness of early signs of illness and began watching their animals closely for mild neurologic signs. Because of this communication, I feel that the last two cases were presented to the hospital earlier in the progression of disease. Although the outcome for these animals was the same, in the future, this communication and cooperation between farms may help save lives and valuable breeding stock.

Two other positive outcomes of this past fall’s tragedy are publicizing that camelids are susceptible to EEE when in the very recent past it was thought that they were not affected by this virus. The second is the research projects that have been stimulated. We are currently gathering scientific evidence about the natural frequency of this disease and performing a trial with an equine vaccine (test animals have been kindly donated by local breeders) to start investigating the possibility of vaccination to help prevent EEE outbreaks in the future.