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Examples: Disease resistance in animals

Chickens Resistant to Bird Flu

Once a bird is infected, avian influenza virus is very easily spread amongst other birds and in some cases to humans. Because of this, if even one chicken is found positive for the virus often the only recourse to contain the disease is to kill the entire flock.  Bird flu is a significant problem from both an economic and food security perspective.  Researchers at the Roslin Institute at the University of Edinburgh have developed chickens that do not transmit the avian influenza to other chickens they are in contact with.  Although the birds will still show clinical symptoms of the disease they will not infect other birds, effectively slowing down and potentially stopping an outbreak within and between flocks.  The birds have been modified to produce a small specifically designed molecule, which diverts and binds the flu virus enzymes, which are vital for its replication.  Other than this small change there is no observable difference in the health, development, or growth of these outbreak-stopping chickens.

Further research is currently being done to go beyond preventing bird-to-bird transmission, such as development of new inhibitors and decoy molecules to create greater resistance to bird flu as well as a wide range of other diseases.  Ultimately this work is being done to reduce risk of avian transmitted epidemics to human populations.



PRRSV Resistant Pigs

Porcine reproductive and respiratory syndrome virus, or PRRSV, is responsible for one of the most costly diseases in the pork industry. It causes respiratory disease in young pigs resulting in reduced growth performance or death and can cause pregnant sows to lose their litter or deliver persistently infected low birth weight piglets. Two groups, one at the University of Missouri and one at the Roslin Institute in Scotland, tackled this disease by using gene editing to change the CD163 gene that is responsible for making the receptor on the surface of pig cells to which the virus can bind to initiate infection. They modified part of the receptor that directly interacts with the virus, making the virus unable to bind the receptor and infect the pigs. When challenged with PRRSV, the gene edited pigs were resistant to the disease.




Trypanosome Resistant Cows

Trypanosomes are parasites transmitted through the tsetse fly that cause a wasting disease in both cattle and humans. This disease, trypanomiasis, is prevalent in cattle in 36 countries in sub-Saharan Africa and is one of the most significant diseases threatening production of healthy livestock in affected areas. Cattle in these regions are important not only as sources milk and meat but are also working animals that contribute to the production of crops. Trypanomiasis in cattle therefore contributes greatly to human suffering through losses in food production. Despite the advantages of owning cattle in these regions, the presence of infected livestock can be a source of human infection. Trypanomiasis in humans, sleeping sickness, effects the central nervous system is generally fatal if left untreated. Despite efforts to breed disease tolerant animals, the trait proved to be too complex and has not reduced the reservoir of trypanosomes in animals threating humans.

Researchers at New York’s Hunter College have been studying the mechanism of resistance to trypanomiasis and discovered a novel protein (Trypanosome Lytic Factor (TLF)) capable of killing the causative parasite. A transgenic approach has been undertaken to develop a breed of cattle able to express TLF making them resistant to trypanomiasis. Currently a bull carrying the baboon TLF gene has sired two offspring that will be the foundation of breed of cattle able to reduce the disease burden of trypanomiasis in both cattle and humans.