Darwin Chronicles

June 2005

Equine influenza jumped species; caused one canine flu outbreak

Greyhounds in at least six states have died from a mysterious respiratory illness, which University of Florida researchers said might be from an equine influenza virus that jumped the species barrier.

Veterinarians investigated one outbreak, which occurred in Jacksonville, Fla., in January. During this outbreak, eight of 24 racing greyhounds that developed respiratory symptoms died.

“I want to stress that our team’s findings are preliminary and confined to the dogs affected by an outbreak at one Florida track, an outbreak that occurred three months ago and was contained through a voluntary statewide quarantine, which is no longer in effect,” said Cynda Crawford, DVM, PhD, a veterinary immunologist from the University of Florida, who spearheaded the research funded by the University of Florida College of Veterinary Medicine Racing Laboratory and the state’s division of pari-mutuel wagering, which regulates greyhound racing in Florida. Crawford could not be reached for comment, but the university provided a press release and an abstract scheduled for presentation at an upcoming veterinary meeting posted on ProMED-mail (www.promedmail.org).

The researchers collected blood and nasal samples from sick and convalescing dogs as well as from two additional dog populations in Florida, including randomly selected pets and racing greyhounds from a track in South Florida. Samples were collected from 35 dogs, and veterinarians performed postmortem examinations on five of the dogs that died. Both control groups tested negative for equine influenza virus, but influenza A subtype H3N8 was isolated from the lungs of two dogs, both of whom died. According to CDC researchers, this strain of influenza is an equine strain.

Equine influenza virus comes from the same group of viruses that caused influenza in people, according to the release, but Crawford said there was no indication at this time that the virus could cause human infection. The disease is present in horse populations throughout Europe, North America and parts of Asia. Horses typically develop a fever and a dry hacking cough; they are reluctant to eat or drink for several days but usually recover in two to three weeks.

With 16 tracks, Florida is the leading state for greyhound racing, according to the National Greyhound Association. Respiratory disease outbreaks in greyhounds appear generally in winter and early spring. The last significant outbreak occurred in March 2003, when state officials approached University of Florida scientists for help. A respiratory illness also struck greyhounds at tracks across the nation in 1999.

Ed Dubovi, PhD, director of the virology section at Cornell’s Animal Health Diagnostic Lab, tested the samples. “Cornell’s virology group is one of the best in the country, and Dr. Dubovi cracked this,” Crawford said in the release. “He was able to isolate an influenza-like virus, which he then sent to the CDC, which routinely monitors influenza outbreaks involving interspecies transmission to determine if there is a threat to public health.”

On the basis of genetic sequencing, Ruben Donis, PhD, and his colleagues at the influenza branch at the CDC concluded that the virus found in the canine samples resembled H3N8 that appeared in horses in Wisconsin last year.

“The virus found in the canine samples is probably representative of the strain that is circulating now in horses in Florida and elsewhere in the United States,” Donis said, adding that to strengthen its findings, the CDC plans to sequence the entire genome of the canine virus.

The dogs developed antibodies specific for the influenza virus, adding more weight to their findings.

The scientists say they have no idea how the Jacksonville greyhounds were exposed to equine influenza virus, but they will continue to research these outbreaks. Although the researchers stress that the findings involve only these particular Jacksonville dogs, they will investigate possible connections to similar disease outbreaks that have affected racing dogs in Florida and elsewhere in recent years.

Crawford said dog owners should not experiment with prevention products approved for other species because of the potential for extremely negative consequences, including death.

Crawford said there was no evidence that the virus posed any significant threat to people or their pets. – Marie Rosenthal

ProMED-mail, the Program for Monitoring Emerging Disease, is a program of the International Society for Infectious Diseases. For information and free subscription, go to www.promedmail.org.

Rodents suspected of infecting transplant patients with LCM

Lymphocytic choriomeningitis (LCM), a viral infection that presents as aseptic meningitis, encephalitis or meningoencephalitis, appears to have caused three deaths in organ transplant recipients, according to the Rhode Island Department of Health.

The common house mouse is the primary host, but pet rodents, such as hamsters, can also carry the virus. About 5% of mice throughout the United States carry this virus, according to the CDC (MMWR 2005;54:1-2).

This is the second report of LCM transmission through organ transplants. In 2003, four transplant recipients from Wisconsin died of LCM. In 1975, 181 symptomatic cases were identified in 12 states. The cases were associated with pet hamsters from one distributor. There were no deaths.

In these new deaths, a trace-back investigation found that the people received organs from the same Rhode Island organ donor, who died of stroke. Kidneys, liver and lungs were transplanted to four people in Massachusetts and Rhode Island. All but one died shortly after the transplant. The donor’s pet hamster tested positive for LCM, although tissue and blood samples from the donor tested negative.

“We continue to investigate the source of infection and events leading to this sad outcome,” said David R. Gifford, MD, MPH, director of health at the Rhode Island Department of Health.

This is only the second time LCM transmission through organ transplant has ever been seen, a release from the department of health said. Public health officials are trying to determine the risk to the public from LCM in pet hamsters.

People can prevent LCM infection by avoiding or minimizing direct physical contact with wild rodents or exposure to rodent urine, feces or saliva, according to the CDC. Transmission may occur when these materials are directly introduced into broken skin, the respiratory system and, perhaps, through a bite by an infected rodent, according to the CDC.

LCM in humans is underreported, and infections can be asymptomatic. The CDC said LCM infection in humans ranges between 2% and 5%. In those who develop frank infection, symptoms begin eight to 13 days after exposure. There is a characteristic biphasic febrile illness as well as any or all of the following symptoms: fever, malaise, lack of appetite, muscle aches, headache, nausea and vomiting. Patients may also experience sore throat and cough as well as pains in joints, chest, testicles and the salivary gland, according to the CDC.

Following a few days of recovery, the infection begins a second phase consisting of meningitis or encephalitis symptoms. Hydrocephalus may occur. Rarely, infection causes myelitis or myocarditis. LCM is not normally fatal, and most people who develop meningitis or encephalitis recover completely, although they may suffer long-term sequelae.

LCM infection has also been associated with miscarriage and neurological illness in newborns, so pregnant women should take precautions and avoid exposure to rodents, especially during the first and second trimester of pregnancy, Gifford said. – Marie Rosenthal

South American moth reeking havoc in Florida

A South American moth is attacking valuable ornamental cactus plants used in landscaping in Florida and could be a threat to the nation’s $70 million cactus industry.

First spotted in the Florida Keys about 15 years ago, the tiny moth has already spread northward to Alabama and South Carolina. The invasive pest could spread even farther, attacking natural and cultivated prickly pear cacti in other areas of the United States, according to University of Florida entomologists. The insect feeds only on prickly pear cacti.

Jim Cuda, an associate professor of entomology at the University of Florida’s Institute of Food and Agricultural Sciences, said in a release that residents should watch for the cactus moth, Cactoblastis cactorum, and the damage it causes in yards, plant stores and nurseries. People should report suspected infestations to the Department of Agriculture (USDA).

Cuda, who believes the spread of the insect may have been hastened by the 2004 hurricanes, said the pest is troublesome because it has no natural predators.

The USDA and others are trying to control the prickly pest. They are looking at a sterile insect release program as well as the feasibility of importing effective biological controls. “Widespread use of pesticides is not practical because the pest potentially inhabits thousands of square miles in Florida alone, including habitat for the endangered Schaus swallowtail butterfly,” Cuda said in a release.

The moth is one of several recent insect invaders to threaten ornamental and food crops in Florida, along with the pink hibiscus mealybug, Asian citrus psyllid and diaprepes citrus root weevil, Cuda said.

The moth can fly short distances, but is mostly spread when infested plants are shipped to another location. Telltale signs of infestation are tiny stacks of eggs on the sides of the fleshy cactus pads. The stacks look like inch-long cactus spines. When caterpillars hatch, they burrow into cactus pads to feed, leaving tiny holes that ooze green slime.

“Once something as tiny as this moth gains a foothold in an area where it has no enemies, stopping it is almost impossible,” said Richard Moyroud, chairperson of the Florida Endangered Plant Advisory Council and owner of Mesozoic Landscapes, a native plant nursery in Lake Worth, Fla. – Marie Rosenthal

Infectious prion proteins invade and move within brain cells

For the first time, scientists have watched the prions that cause transmissible spongiform encephalopathies (TSEs) as they invade nerve cells and enter the brain.

These findings may help to better understand TSE diseases and may lead to ways to prevent or minimize their effects. TSE diseases include scrapie in sheep and goats, chronic wasting disease in deer and elk, mad cow disease in cattle and Creutzfeldt-Jacob disease in humans. Under the direction of Byron Caughey, PhD, at the Rocky Mountain Laboratories (RML) in Hamilton, Mont., and Marco Prado, PhD, at the Federal University of Minas Gerais in Belo Horizonte, Brazil, researchers performed the research in laboratory cultures using a rodent-adapted form of scrapie protein and cells taken from the central nervous system of mice and hamster brains. Researchers branded the proteins with fluorescent dyes.

“When I started working on TSEs, I thought about them as being similar to intracellular bacterial pathogens — something that replicates within an animal or human host cell,” Gerald Baron, PhD, a lead researcher at RML, said in a release. “I wanted to know how such a pathogen binds to the host cell and how it enters, replicates and spreads to other cells.”

Baron said researchers have tracked infectious prion proteins moving through other parts of animal bodies up to the brain, but no one had ever tracked the proteins movement within animal brain cells. One of the most difficult aspects of the experiment, he said, was finding a way to tag the TSE prion proteins with a fluorescent dye without altering it, while still allowing researchers to identify the prions as they penetrated the cells and spread within the long projections that nerve cells develop to send signals to other nerve cells.

“This was difficult from a technical aspect because the scrapie pathogen is largely a corrupted form of a host cell protein,” Baron said. “It can be hard to detect the corrupted prion protein in living infected cells and distinguish it from its normal counterpart.”

Once researchers learned how to mark the prion proteins, they added them to a culture of nerve cells and watched them, taking photo images with a confocal microscope. Confocal microscopy uses laser light to scan many thin sections of a fluorescent sample, resulting in a clean three-dimensional image. The painstaking job of analyzing and deciphering about 1,000 different images primarily belonged to Ana Cristina Magalhães, PhD, from the Federal University of Minas Gerais, who filled a file cabinet drawer with CDs containing microscopic images. The effort results in striking photos that, when formatted for video, show prion proteins moving within cells, then along narrow cellular projections called neurites and ultimately into close proximity with adjacent cells.

The work also revealed that a similar trafficking process might occur with the key plaque-forming protein in Alzheimer’s disease, which is not a TSE but a different type of degenerative brain disease, according to Baron.

The report appeared recently in The Journal of Neuroscience (2005;25:5207-5216). – Marie Rosenthal