Breakthroughs Blog: Zika

In this regular feature on Breakthroughs, we highlight some of the most interesting reads in global health research from the past week. During the recent Ebola epidemic in West Africa, an experimental drug, ZMapp, showed promise in treating the disease, but with only enough doses to treat seven people, the drug’s true impact remained unknown. Now, results of a randomized control trial conducted during the outbreak indicate that ZMapp likely increases a patient’s chance of survival, but fall just short of statistical significance. The researchers hoped to enroll 200 patients across Liberia, Sierra Leone, and Guinea, however, as the number of new cases waned, so too did eligible participants for the trial. Ultimately, the team recruited only 72 participants, all of whom received the standard care for Ebola and half of whom also received ZMapp. Further complicating the results, many of the patients were enrolled after the virus had already caused irreparable tissue damage and did not survive long enough to receive all three doses of ZMapp. The results suggest high probability—91.2 percent—that ZMapp is effective against the virus and confirm the drug’s safety. ZMapp is composed of three antibodies against Ebola, and research is underway to develop improved antibodies which could enhance the drug’s efficacy. Viruses are constantly mutating, and often incorporate genes from the organisms they infect—viruses that infect bacteria often have bacterial DNA and viruses that infect animals often have animal DNA. The WO virus targets the bacteria Wolbachia, which in turn targets spiders and insects. Consequently, when researchers at Vanderbilt University sequenced the genome of WO, they expected to find snippets of Wolbachia DNA. Instead, they found that one third of WO’s genes came from the arthropods that Wolbachia infects. Further, WO contains genes for latrotoxin, the chemical cornerstone of the venom found in black widow spiders, a particularly surprising discovery as latrotoxin has never been reported outside of spiders. The scientists suspect WO’s unique evolution relied on the way Wolbachia intertwines itself with animal cells, requiring WO to drill through the animal cell membranes to reach the bacteria. Zika virus, first discovered in 1947, was long considered innocuous, rarely reported in humans and associated with a mild infection. The virus raised concern, however, when scientists discovered its connection to microcephaly—a birth defect in which an infant’s brain does not develop properly, resulting in an abnormally small head. Now, one year after a spike in microcephaly cases in Brazil led to this important discovery, infants with what’s been deemed congenital Zika syndrome are coping with a range of devastating symptoms not usually reported in infants with microcephaly, including seizures, impaired vision and hearing, difficulty swallowing, and arm and leg deformities. Additionally, some infants have presented with neurological and physical defects despite having normal-sized heads and others still have developed microcephaly after birth, as the growth of the head has not kept up with that of the body.

Scientists have devised a Trojan horse strategy to prevent the Ebola virus from infecting human cells. To infect humans, the virus binds to the surface of a human cell, enters the cell, and then binds to the protein Niemann-Pick C1 (NPC1). Once it binds to NPC1, the virus can start replicating and spreading throughout the body. Consequently, the researchers first engineered two antibodies: one that targets the human protein NPC1 and another that targets the viral protein that binds to NPC1. However, they needed a Trojan horse: a molecule that could deliver the antibodies to the scene of the crime, deep inside human cells, where the virus binds to NPC1. The solution? The team synthesized each antibody with a third antibody that binds to the surface of the Ebola virus. In short, the team created two molecules by combining the antibody that could latch onto the virus with two antibodies that could prevent the virus from infecting human cells. Both combinations proved effective in the lab against all five strains of the Ebola virus and in mouse trials, one of the molecules effectively treated infected mice. Next, the molecules will be tested in nonhuman primates. A recent piece in STAT takes an in-depth look at the critical advances in hepatitis C research that paved the way for the development of Sovaldi, the first drug proven to cure hepatitis C. Hepatitis C was first discovered in 1989, however, the virus is notoriously difficult to reproduce in the lab. Consequently, the time and cost of producing the virus hindered research. Ralf Bartenschlager and Charles Rice, researchers at the University of Heidelberg and Rockefeller University, respectively, determined that certain mutations of the virus enabled select strains of the virus to survive in the lab, and engineered versions of the virus—deemed “replicons”—with those mutations. Using these replicons, drug companies were able to rapidly screen the efficacy of different compounds in combatting hepatitis C. Among these companies, the small biotech firm Pharmasset developed a particularly promising drug, which was eventually—after the company was acquired by Gilead Sciences—approved and marketed as Sovaldi. The drug became the first cure for Hepatitis C, however, its price tag of up to US$94,000 for the full regimen has impeded access to it. While existing evidence suggests that Zika infection has the greatest impact on fetal brain development during the first trimester of pregnancy, new research indicates that infection later in pregnancy can still have a devastating impact. Scientists at the University of Washington infected a pregnant monkey with the virus at the beginning of her third trimester, and in less than a month, significant damage to the fetus was reported: both the white matter in the brain and the head itself stopped growing. However, the team administered the virus in higher doses than would be found in individual mosquitoes, and researchers at the University of Wisconsin-Madison, who used lower doses, found no fetal brain damage after infecting four pregnant monkeys.

In this regular feature on Breakthroughs, we highlight some of the most interesting reads in global health research from the past week. In this edition, we cover new insights into the impact of the Zika virus on the brain. Researchers have released medical images of 46 fetuses and infants born to women who were infected with the Zika virus during pregnancy, revealing serious brain damage beyond microcephaly. The images, which include 23 MRI scans, 41 CT scans, and 93 ultrasounds, were taken at Instituto de Pesquisa in Campina Grande State Paraiba in northeastern Brazil and analyzed by neurologists at the Instituto in partnership with a team at the Beth Israel Deaconess Medical Center in Boston. The brain damage manifests in distinct ways: many of the scans showed skulls filled with cerebrospinal fluid, and in one case there was so little brain tissue that the skull collapsed in on itself, resulting in a flattened skull with extra skin. The images indicated damage to the brain stem, which regulates breathing and heart rate; the cerebellum, which is responsible for motor control; and the cortex, which is involved for learning, memory, emotion, and language. New research suggests that Hofbauer cells, found in the placenta and tasked with protecting the fetus from pathogens, may be the key to the Zika virus' ability to cross the maternal-fetal barrier. Hofbauer cells are macrophages, immune cells that combat pathogens by consuming them. However, dengue virus—a flavivirus related to Zika—is able to hijack macrophages, using them to replicate and disseminate throughout the body. While the researchers have confirmed that the Zika virus is able to survive within Hofbauer cells, they suspect that the immune cells may also be enabling the virus to travel to the fetal brain. The study also confirms that the virus can replicate within fibroblasts, a critical component of the placenta’s structure, a finding described as, “a bit of a surprise,” by one of the study’s authors. Scientists at Rockefeller University have also described their recent findings as "kind of a surprise," in this case, that certain adult brain cells are also susceptible to the virus. Fetal brains are primarily comprised of neural progenitor cells; while these stems cells are not as ubiquitous in adults, they play a critical role in learning and memory. Earlier this year, researchers determined that fetal neural progenitor cells are particularly vulnerable to Zika. Now, the team at Rockefeller has confirmed that adult neural progenitor cells are no exception. The study revealed an increase in cell death but a decrease in the production of new brain cells in infected adult mice. More research is needed to determine how this translates to humans, however, such damage could increase risk for cognitive challenges, depression, and Alzheimer’s disease.

Penicillin, the world’s first antibiotic, works by targeting certain proteins—appropriately named penicillin-binding proteins (PBPs)—that play a critical role in building and maintaining the bacterial cell wall. Now, scientists at Harvard Medical School have identified another class of proteins which play a similar role and could be a target for the next generation of antibiotics. The road to discovery started in 2003, when it was determined that certain bacteria could grow without PBPs. In their absence, the proteins responsible for maintaining cell wall shape, elongation, division, and spore formation (SEDS proteins) continued to function normally, enabling the bacteria to thrive. SEDS proteins are found in more types of bacteria than PBPs, and consequently a treatment targeting SEDS proteins could have even broader application than penicillin. On February 22, the Obama Administration requested US$1.9 billion in emergency funding for the Zika response, and 181 days later, Congress has yet to approve it. Consequently, the Department of Health and Human Services (HHS) has shifted $81 million from other programs to support Zika vaccine research and development—$34 million of which will go to the National Institutes of Health (NIH) and $47 million of which will be allocated to the Biomedical Advanced Research and Development Authority (BARDA). Earlier this year, HHS repurposed $589 million in funding from the Ebola response to combat Zika, however, that funding will run out by the end of this month. The NIH will use its funding for human clinical trials of its leading Zika vaccine candidate, however, the agency will need an additional $196 million for additional trials and to advance a second and third candidate. BARDA’s funding will enable the agency to secure contracts and establish partnerships for Zika vaccine development, however, an additional $342 million will be required to continue its work. New research suggests that infection with the Plasmodium parasite, which causes malaria, could reduce the severity of Ebola infection. A team of scientists at the US National Institute of Allergy and Infectious Diseases has examined 1,868 blood samples from an Ebola treatment unit in Liberia—1,182 of which tested positive for Ebola—concluding that patients co-infected with malaria were 20 percent more likely to survive. These results held true even when controlling for the patient’s age and viral load. Viral load actually correlated with survival rates: those with the highest levels of Plasmodium had an 83 percent survival rate, compared to 46 percent of those only infected with Ebola. At the treatment center, all patients were provided with antimalarials, and consequently, treatment for malaria was not responsible for survival rates. While the reason for this trend remains a mystery, Drs. Emmie de Wit and Kyle Rosenke—the study’s lead scientists—suspect that an existing malaria infection expedites the immune response to Ebola, consequently increasing survival rates.