Vaccines targeting the innate immune systems of invertebrates could be a major boon for agriculture
People are getting vaccinated. Cats and dogs get vaccinated. Cows, fish and even koalas get vaccinated. As part of a shift in the way researchers think about immune protection, invertebrates are now also getting vaccinated.
The first bee vaccine received conditional approval from the U.S. Department of Agriculture three years ago and began rolling out to farms across the United States and Canada. Last month, at the World Vaccine Congress in Washington, DC, the company behind the vaccine announced early testing results of a potential shrimp vaccine.
These developments could be big news for agriculture. The beekeeping industry is valued at over $10 billion, with losses due to diseases and pests estimated at hundreds of millions of dollars each year. For shrimp aquaculture, valued at tens of billions of dollars, disease-related costs could run into the billions of dollars. Strengthening the immune systems of invertebrates could stave off these diseases while reducing the need for antibiotics, which may encourage antibiotic resistance.
But unlike humans and other vertebrates, invertebrates do not have an adaptive immune system. This is the system that vaccines typically exploit to make antibodies that mark specific pathogens for destruction. Although invertebrates, like vertebrates, possess innate immunity, this form of immunity has not been widely considered a vaccine target in itself. The innate immune system is generally less specificprimarily targets features found in broad classes of pathogens and does not recognize or remember pathogens in the same way that the adaptive immune system does.
“For a long time, it was considered impossible, as if vaccination couldn’t happen,” said Erin Strait, veterinarian and chief scientific officer of Dalan Animal Health, the animal health organization. company behind vaccines. “In recent years this has proven not to be true.”
Over the past few decades, it has become increasingly clear that the innate immune system has its own means of creating immune memory. Scientists believe that this memory is achieved through epigenetic changes, modifications to DNA that do not alter its genetic sequence, and that these epigenetic changes can be passed down from one generation to the next. This is how Dalan’s team thinks its invertebrate vaccines work.
The existing vaccine for bees is made from inactivated viruses Paenibacillus larvaea bacterial pathogen that causes American foulbrood, a disease that infects and kills bee larvae. When the vaccine is given to the queen and she reproduces, her offspring become more resistant to these bacteria, as well as to a varroa bee-borne virus.
For the potential shrimp vaccine, inactivated bacteria — Dalan did not disclose the type — are given to a brood stock that breeds to produce a new generation that inherits immunity. These shrimp babies are born vaccinated.
In a proof-of-concept laboratory trial, vaccinated shrimp were exposed to Vibrio parahaemolyticus bacteria, which cause early mortality syndrome, and another pathogen called white spot syndrome virus. For shrimp exposed to V. parahaemolyticusvaccination increased survival from 27 percent to 48 percent. For shrimp exposed to the virus, vaccination increased survival from zero percent to 58 percent.
While traditional vaccines are specific to a single pathogen, bee and shrimp vaccines appear to offer protection against multiple pathogens. In shrimp, this protection is specifically intended for pathogens different from that used in the vaccine.
Although a shrimp vaccine could be helpful, Arun Dhar, a crustacean infectious disease researcher at the University of Arizona in Tucson, would like Dalan Animal Health to publish its data in a published paper before commenting on its promises. He has studied shellfish pathology for many years and is skeptical of potential vaccine candidates. “The field data would really indicate true effectiveness,” he says.
Dalan is moving toward field trials in Southeast Asia, starting with Indonesia, that could provide such data and lead to regulatory approval.
Other teams have also worked on shrimp vaccines, but challenges include a limited immune response in juvenile shrimp. Dalan avoids this problem by administering the vaccine to adult shrimp who then pass on immunity to their offspring.
If these vaccines prove effective, other invertebrate species could also be candidates for vaccination, particularly those used in agriculture. Applied entomologist Christopher Williams of Liverpool John Moores University suggests that vaccines against silkworm pathogens would be attractive. His work showed that probiotic interventions could also protect against the pathogenic fungus. Beauveria bassianawhich grows on silkworms, destroys their cuticle and releases toxins, ultimately killing them.
