Rabies, the disease that drives infected victims wild, is almost always fatal once it reaches the brain. A new finding from two remote communities in the Peruvian Amazon may reveal a chink in the virus's armor. Scientists have tested six native people there who have never received a vaccination yet appear to have developed natural antibodies to the virus. The researchers think that vampire bats, common in the region, bit the sleeping humans and passed along small amounts of the virus over time. The multiple, low-dose exposures gave each person’s immune system a chance to learn how to fight back.

The scientists, from the Centers for Disease Control and Prevention (CDC) and the Peruvian Ministry of Health, made their finding during a search for emerging infectious diseases harbored by bats. They surveyed two communities, Truenococha and Santa Marta, which are respectively two and six hours away from the closest health post and only reachable by boat. "Generally the communities don't appreciate the risk of rabies from a bite," says Amy Gilbert, a postdoctoral fellow at the CDC's National Center for Emerging and Zoonotic Infectious Diseases, who co-led the work. "They don't know how it is transmitted and are unlikely to seek treatment because of the low perceived risk and because care is very far away."

Gilbert and her fellow researchers interviewed 92 people in the two communities and drew blood samples from 63 of them. They found seven individuals who had antibodies that could trigger a fight to neutralize rabies. All of the people reported exposure to bats, whether through a bite, scratch or just a brush against bare skin. Only one of the seven had received vaccine after being exposed, however. The findings were published in the August 2012 issue of the American Journal of Tropical Medicine and Hygiene.

The researchers do not know exactly how the antibodies arose, Gilbert explains. The most likely explanation is that multiple bites over time gave these individuals a low does of live virus—enough to develop an immune response without a full-blown central nervous system infection. "We don't have any evidence that these people had the clinical presentation of the symptoms associated with rabies," Gilbert says. It is possible that the native population, long subject to vampire bats, may have developed genetic protection against rabies. Or this particular strain of rabies is less virulent. The researchers have no data to back either conclusion, but they also cannot rule them out.

"This study is based on a very small amount of scientific data," says Craig Hooper, an immunologist at Thomas Jefferson University not involved in the work. The interviews are an interesting, rich source of information, he says, but the six people who may have developed natural immunity have very low levels of antibody. Additionally, the levels were observed by only one, fairly conventional, technique. More sensitive tests taken over time could reveal when the individuals were infected and how fiercely the infection raged, he says.

Rabies jumps from host to host through the bite of an infected animal. The virus itself travels from the wound to the brain through an unusual highway. Instead of swirling through the blood, it creeps along nerve fibers. This slow progress explains the variable timing of symptoms following a bite: the farther the bite is from the brain, the longer the virus must crawl. The time lag also gives bite victims the opportunity to seek treatment. A vaccine and treatment with rabies-specific antibodies, even after a bite, arms the immune system to fight off the virus. Contrary to popular belief, the post-exposure treatment for previously unvaccinated people is just four shots to the upper arm over two weeks. People who have been previously vaccinated for protection against the virus only need two shots. The critical moment is when the virus reaches the central nervous system (CNS). Without treatment, weeks or months after an attack the virus triggers a full-blown CNS infection, complete with slavering, snarling, aggression and hydrophobia. At this point, it is usually too late for even the best medical treatment.

9 Comments

1. 1. Traveler 007 06:38 PM 8/2/12

   "Bites from Vampire Bats Might Protect People against Rabies"
   
   The bad part is that you won't show up in a mirror anymore and are doomed to walk the earth as a living dead.
   

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2. 2. singing flea 11:02 PM 8/2/12

   So, who want's to volunteer for a fun science project?

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3. 3. LisaZ 11:06 PM 8/2/12

   Ha! In a dozen years in Latin America, I've been bitten five times by bats. (Costa Rica, Nicaragua, Ecuador) Believe me, I wasn't very happy to discover the bites in the morning.
   
   Reading this gives me a touch of emotional relief - wonder if I have developed any antibodies against rabies?
   Z

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4. 4. jaypatela 10:52 PM 8/5/12

   Quite interesting. I would be cool to see if the genes have actually changed to encapsulate a rabies resistant gene caused by the repeated rabies exposure. Who knows, they could be a population that is postively favored by natural selection...

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5. 5. jimfromcanada in reply to LisaZ 12:59 PM 8/8/12

   I would take the rabies shot since the article points out that CNS infection is sometimes delayed since the virus moves slowly along the nervous system and not through the bloodstream but once it is in the CNS it is fatal.
   

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6. 6. ironjustice 01:09 PM 8/12/12

   In theory , couldn't a person fight off an infection and live ? The body is designed to do just that. If a person were , say , more inclined to fight off , mount and EFFECTIVE immune response then the person may , have the time TO ,develope the antibodies , due to the fact they were not killed ?
   "Lactoferrin, an iron-binding glycoprotein synthesized by neutrophils and Lactoferrin, an iron-binding glycoprotein synthesized by neutrophils and exocrine glands, plays an important role in human innate defense mechanisms against bacteria, fungi, and viruses.
   exocrine glands, plays an important role in human innate defense mechanisms against bacteria, fungi, and viruses."
   This 'window' , survival , would have given them that immunity to rabies ? The immune system is based on the removal of iron from an invader , virus or bacteria by the lactoferrin and IF these people were low in iron and DID mount an effective response , IE: anemia of chronic disease / lactoferrin / iron sequestration away from the rabies virus , THEN the person would naturally gain the antibodies , survival induced , and be able to suppress any further onslaughts by this virus ? BUT when one ISN'T able to mount this effective defence , anemia of chronic disease , THEN the virus kills you , and the antibodies are obviously therefore of little use ?
   

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7. 7. ironjustice 01:52 PM 8/12/12

   The body produces a substance which stops virus' at the door. Lactoferrin.
   "Lactoferrin probably exerts its effect at the level of viral adsorption"
   Lactoferrin removes iron , a requirement of virus , bacteria , fungi and thereby disallowing the virus to establish itself in the body , IE: anemia of chronic disease.
   "Antimicrobial and antiinflammatory effect of lactoferrin by chelation of iron"
   When lactoferrin is partially saturated , its ability to stop the invasion is diminished greatly.
   "Low iron-saturated LF effectively combats bacteria and fungi, acting in a bacteriostatic and fungistatic way. The degree of iron saturation also influences antiviral activity of LF. "
   When the body has too much iron the lactoferrin becomes saturated and cannot stop the invader at the door .
   
   "Characterization of antiviral activity of lactoferrin against hepatitis C virus infection in human cultured cells"
   "The results suggest that iron deposition in hepatocytes could facilitate HCV infection in the liver"
   "Lactoferrin inhibits hepatitis C virus viremia in patients with chronic hepatitis C: a pilot study."
   
   Lactoferrin is a globular protein found in milk and many mucosal secretions such as tears. Its molecular atomic mass is 80,000 u (80 kD). This protein belongs to the transferrin family proteins (transferrin, melanotransferrin, ovotransferin, etc.) showing a high
   affinity by iron (ferric state). Lactoferrin is a multifunctional protein with antimicrobial activity (bacteriocide, fungicide) and is part of the innate defense proteins mainly at mucoses. ...
   en.wikipedia.org/wiki/Lactoferrin
   
   

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8. 8. ironjustice 10:37 AM 8/13/12

   These two studies seem to go against everything we have been told about hepatitis ? They tell us we cannot pass the virus by anything but blood but these studies refute this. So does it mean , HIV , too , is passed in the sweat ?
   
   "Hepatitis C virus replicates in sweat glands and is released into sweat in patients with chronic hepatitis C."
   
   "Findings from a study of Olympic wrestlers indicate that hepatitis B is found in the sweat of infected individuals, and so sweating might be a way that the virus could be passed between participants in contact sports."
   

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9. 9. ironjustice 09:57 PM 8/17/12

   This is an example of excess iron and its effects on a virus.
   "Researcher with hereditary hemochromatosis who died from laboratory-acquired plague"
   This scientist had iron overload and by working with the vaccine , it became virulent BECAUSE he had this iron load , and it killed him.
   He should be hailed as a hero.
   
   "Hereditary Hemochromatosis Restores the Virulence of Plague Vaccine Strains."
   "Should not be exposed to live-attenuated plague vaccines"

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