Dr. Karl Brantly and Nancy Writebol were working at a hospital in Liberia, where it is believed they contracted the deadly Ebola virus - responsible for 961 deaths during the current outbreak, according to the World Health Organization (WHO) as of August 6th.
At present, treatment for the disease is limited to intensive supportive care. However, the missionaries were offered the opportunity to be given ZMapp - an experimental drug that had previously only been tested on monkeys - and it looks as though the treatment may have saved their lives.
Dr. Scott Podolsky, associate professor of Global Health and Social Medicine at Harvard Medical School, has written in the Annals of Internal Medicine that ZMapp has much in common with methods of treating illness that were being developed toward the end of the 19th century.
History repeating itself?
The experimental combination of pre-formed monoclonal antibodies given to the two American missionaries is one of several potential Ebola treatments that are currently being developed.
ZMapp is a three-mouse monoclonal antibody; it was made by collecting the antibodies created in the blood of mice after exposing them to fragments of the Ebola virus. Podolsky writes that this method mirrors that of passive serotherapy that was developed over a century ago.
The methodology, he writes, first began to be developed following the discoveries of microbiologists Louis Pasteur and Robert Koch, who started to identify the agents of diseases such as anthrax, diphtheria and pneumonia.
By 1890, humoral factors were then discovered in infected animals that could be transferred into laboratory animals to protect them from the toxins of diphtheria and tetanus.
Podolsky writes how this discovery led to treatment for humans:
"From the 1890s onward, this model of production - expose an animal (guinea pig, rabbit, cow, horse, etc.) to an identified microbial pathogen, generate antibodies (or use convalescent serum from former patients), and then 'passively' transfer the pre-formed antibodies to an exposed animal or person - could be expanded to such feared and prevalent diseases as pneumococcal pneumonia and meningococcal meningitis."
Serotherapy was refined during the first half of the 20th century in controlled studies that focused on pneumococcal pneumonia, referred to by some as "the Captain of the Men of Death."
Serotherapy was found to be effective when targeting particular strains of the disease. Podolsky writes of "once-moribund patients described as sitting in their beds reading the newspaper the following morning," following serotherapy.
In some cases, it was able to affect recovery in patients who had previously been considered to be on the brink of death, mirroring the dramatic turnaround in the case of Dr. Karl Brantly. Only days before receiving ZMapp, Brantly had called his wife to say a final goodbye. Fortunately for them, this proved to be premature.
What happens next?
Although it looks as though the two Americans could be heading toward recovery, there is still a lot of uncertainty surrounding ZMapp and its role in the future of the Ebola epidemic.
Many are wondering whether the drug will be given to others who have been affected by the outbreak. As ZMapp is still an experimental drug, which before now had not been tested on humans, officials have said that it is unlikely that it would be rolled out for public use without further research.
The missionaries may have been offered ZMapp on compassionate grounds by the drug's manufacturers, as the WHO and Samaritan's Purse (the missionaries' organization) have said that they did not fund the treatment. The drug has not yet been cleared by the US Food and Drug Administration (FDA) for public use.
Theirs appears to be a fortunate case, but it is hopeful that the apparent success of this treatment could inspire the creation of a fully licensed vaccine to combat the threat of Ebola.
Podolsky believes that the earlier era of passive serotherapy can provide further inspiration for the treatments of tomorrow. Antimicrobial remedies such as bacteriophage therapy, probiotics and passive serotherapy all have their origins in the same era and could become increasingly important as more and more diseases develop resistance to antibiotics.
For more information about Ebola and its potential impacts, Medical News Today has a Knowledge Center article that details precisely what Ebola is and how it is contracted.