Antibody fragments produced by horses have been shown to be highly potent in neutralising Covid-19.
Research in Brazil has demonstrated that the neutralising antibodies produced after inoculating horses with the Covid-19 spike protein were up to 150 times more concentrated that those in human convalescent plasma.
In developing countries that do not have effective vaccination programmes, the use of horse antibodies could be an especially effective tool in the fight against the SARS-CoV-2 pandemic, as horses can produce the plasma more cheaply and at higher volumes than in other species.
The research by Cunha et al, published in the journal iScience this week (23 October), is the most recent of five studies into equine Covid-19 antibodies, with work also having been carried out in Argentina, China and Costa Rica.
Cunha et al’s study took plasma from immunised horses and used the digestive enzyme pepsin to purify the antibodies, yielding an F(ab’)2 preparation, an antibody fragment that has two antigen-binding regions.
Hamsters were then used in a challenge study — a type of controlled infection trial.
The use of the equine F(ab’)2 preparation was found to reduce viral load in the hamsters’ pulmonary tissues, while improvement in clinical signs of the virus was also demonstrated by significant weight gain.
The study’s authors said that while more than 20 Covid vaccines had been approved for human use in different countries, the world remained “far from a solution” to the pandemic owing to the “lack of antiviral treatments” for infected individuals.
“The development of virus-neutralising purified hyperimmune globulins produced in horses or llamas may be an approach to treat SARS-CoV-2 infection. The use of llamas to develop passive immunisation therapies is still experimental and limited by animal availability. On the other hand, hyperimmune serum, immunoglobulins or IgG fragments produced in horses have been used to treat many diseases, such as rabies, tetanus, and snake envenomation, among others,” they said.
“Brazil, such as many other countries, has a large established capacity to produce equine hyperimmune globulin preparations for a range of indications, which makes the production of such products against SARS-CoV-2 highly feasible.”
A clinical study this year by Lopardo et al demonstrated improvement in patients infected with Covid-19 after treatment with equine antibodies. It was found to be especially effective in severe cases.
Cunha et al’s study differed from previous work in that it used a different vaccination strategy on the horses, aiming to maximise the formation of the neutralising antibodies.
Their serum was found to be effective against both the Gamma and Brazilian variants of the virus.
The study’s authors said the strategy could be easily reproduced “anywhere in the world” and “could rapidly be tested as a therapy for Covid-19”.
Work on an equine hyperimmune serum in Argentina recently received emergency approval after clinical studies demonstrated a 45% reduction in mortality.
One horse can typically be bled up to six times per year without causing suffering and the study’s authors estimated that 80 horses could produce 100,000 doses of the Covid antibody therapy annually.
Horses are regularly used around the world to produce anti-venoms as well as anti-viral therapies for diseases such as rabies.
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