U. FLORIDA (US) — Genetic analysis may hold the key to finding an effective vaccine against a tick-borne pathogen that costs the U.S. cattle industry as much as $300 million a year.
Even more devastating in developing countries, bovine anaplasmosism can cause animals to develop a fever, have difficulty breathing, and become anemic. Thirty percent of the animals that contract it die.
In the journal Vaccine, veterinary scientists report sequencing the genes of multiple strains of the bacteria from across North America to identify common substances that could be candidates for vaccine development.
“At the DNA level, we examined genes to determine how similar they are among various strains of the disease,” says Michael J. Dark, assistant professor of infectious diseases and pathology at the University of Florida. “If they show similarity, they are probably better vaccine candidates because they would presumably offer cross-protection against multiple strains.”
Although many attempts have been made since the early 1900s to develop a vaccine against Anaplasma marginale, none have provided complete protection against infection with different strains of the bacteria, Dark says. Previous studies have focused on two particular proteins, MSP2 and MSP3, known to protect against certain strains, but which have not yielded universal protection.
Researchers used pyrosequencing to compare multiple strains of Anaplasma marginale and determine which showed fewer DNA changes from strain to strain.
“No vaccine has been proven 100 percent effective against all strains, which is necessary for an effective vaccine,” Dark says. “Ideally, the perfect vaccine would also have other characteristics, such as not needing to be refrigerated; otherwise in places like Africa, you’d never be able to use it. You’d also want a vaccine to be effective quickly and long-lasting, hopefully for the life of the animal, or at least so that it wouldn’t need booster shots every year.”
But, for several reasons, the disease is difficult to defend against.
“We already have vaccines for diseases that are relatively easy to produce vaccines for, such as smallpox in people,” Dark says. “The biology of Anaplasma marginale is more difficult to protect against, because the organism has evolved in order to infect cattle for life. Because of its ability to adapt and evade the immune system, this disease has made our lives that much more difficult in terms of trying to find a vaccine that is effective.”
More is understood about the way in which Anaplasma affects the immune system than is known about many human diseases and even many other tick-borne diseases that affect livestock and other animals, “yet, despite that knowledge, we still can’t create a vaccine that protects against every strain,” Dark says.
Molecular analysis has given researchers useful tools for examining differences between individual organisms, such as information that could be gleaned to yield important epidemiologic information, or determine disease origin.
“We are starting to get into more of the details as to what makes up the organism, but what is the difference between Anaplasma marginale in Florida and in Puerto Rico, and how can we use genetic information to determine where a disease comes from?” Dark says.
“Does every strain from Florida have certain characteristics? Might something work against a disease found in that state but not elsewhere? We have a lot of questions open up when we can look at all these organisms quickly and fairly cheaply at the genetic level, and we can also get more information than we ever have before.”
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