040 - Observations on Attempts to Produce Acute Disseminated Encephalomyelitis in Monkeys, and related studies

This entry will address a few issues relating to vaccines that were very serious, at least in their time. Not so much anymore, fortunately, but I’ll get into that later. A number of studies form the basis of this topic^1–9. Our understanding of the topic has changed over the years, but the fundamental issue is something called encephalomyelitis.

Encephalomyelitis comes in a number of forms, caused by different things, but it’s almost always a disorder of the brain and central nervous system in which the sheaths surrounding neurons/nerve cells, which are made of myelin, get broken down somehow, so the neurons stop working. In the worst cases, this leads to paralysis and sometimes death. One example of this is multiple sclerosis. It’s not pleasant.

How does this relate to vaccines though? Well, for a while it was suspected that the rabies vaccine, which was made from nervous system material of animals that had been infected with rabies, occasionally induced acute encephalomyelitis as a rare side effect⁹. But then in the 1920s, Turnbull and McIntosh observed several cases of encephalomyelitis after vaccinating people against smallpox⁴.

Post-Infectious Encephalomyelitis

The vaccine itself was a live virus, called vaccinia, or cowpox. This was inoculated into people’s arms, where it usually caused very little disease but induced enough of an immune response to protect the person from the much deadlier smallpox.

An article in the Lancet describes Turnbull’s and McIntosh’s observations. They saw 7 cases of post-vaccinal encephalomyelitis (or PVE) in 14 years of vaccinating people at their hospitals in London and Middlesex. The appearance of the disease, especially in autopsy, was distinct from poliomyelitis or other similar things². After this, others observed similar cases of encephalomyelitis in Holland, 35 cases of which 15 were fatal. The researchers didn’t find any vaccinia in the brain tissue though, but they all happened 10-13 days after vaccination. They speculated that there might be some latent infection activated by the vaccinia³.

Vaccinia wasn’t the only infection that could induce such a condition; smallpox itself could too, as well as other fever disorders, especially measles^6,7. Others included chickenpox, influenza, mumps, rubella, and possibly diphtheria, pertussis, and scarlet fever⁸.

According to Ricardo Jorge in the Lancet, the most common cause of encephalomyelitis was measles: one in 250 cases got it, though only 10% of the time was it fatal. More often than that, though, there were long-lasting sequelae, which could include partial paralysis or other impairments. Smallpox caused it in about 1 in 400 cases. Chickenpox-induced encephalomyelitis was relatively mild, while that induced by influenza (largely present in the 1918 pandemic) was variable in its severity. Encephalomyelitis from vaccinia was the most often fatal though⁸.

According to the CDC’s website, the vaccine for smallpox is still capable of inducing such reactions (though only in fewer than 14 to 52 out of a million people vaccinated); it’s not an entirely risk-free treatment. So it’s no wonder that it is not recommended for general use anymore; fortunately, smallpox has been essentially eliminated from the world, so it is no longer needed.

Somewhat puzzling was the frequency of post-vaccinal encephalomyelitis in the 1920s, which seemed to reach epidemic proportions, and then faded away to some extent, for no apparent reason:

"Attention may next be directed to the occurrence of encephalitis after vaccination (ordinary cow-pox), a sequel that has aroused some concern in the course of the last three years, over one hundred cases having been recorded in that time. There can be little doubt that such cases were formerly extremely infrequent, and the conclusion seems justifiable that they are somehow connected with the times through which we are passing."¹⁰

But this mystery, I think, remains unsolved.

Post-Rabies Vaccine Encephalomyelitis

Returning to the issue of encephalomyelitis induced by the rabies vaccine, that too was an unfortunate side effect, but better understood now. According to a paper from 2008,

"The susceptibility of humans to the induction of experimental allergic encephalomyelitis was discovered accidentally when patients were vaccinated against rabies with spinal cords from rabbits that were infected with the rabies virus."¹¹

What this means is that the injection of nervous system material induced an immune response against the myelin that surrounds the nerves. The patient’s own immune system then attacked the myelin, breaking it down, thus causing serious damage to the nervous system itself.

This was quite unfortunate, though rare; Stuart and Krikorian estimated that only 28 to 130 people per 100,000 vaccinated came down with the condition⁹. When you were bitten by a rabid animal, you could be virtually 100% certain that you would die from rabies before too long unless treated with the vaccine, so it was definitely worth the risk. The authors also suggested that adequate preparation of the vaccine material to denature and dilute out the myelin could significantly reduce the potential to cause encephalomyelitis, even in 1930⁹.

Since that time, of course, people have developed rabies vaccines with no myelin contaminating them at all, incapable of inducing an immune response against the recipient’s own brain¹².

Attempts to Induce Encephalomyelitis in Monkeys

All this brings me to the study that is the primary focus of this post¹. Thomas Rivers, Sprunt, and Berry had noted others’ previous observations of encephalomyelitis after vaccine or infection (as described above), though they called it “acute disseminated encephalomyelitis” (or ADE, or sometimes ADEM) instead of post-vaccinal encephalomyelitis or other names; I think ADE in later publications is something distinct from what I’m discussing here.

Anyway, the authors decided to try to induce encephalomyelitis in the lab, in rhesus monkeys, in several different ways, using vaccinia virus and some extracts or emulsions of virus-free body tissues.

First, eight monkeys were vaccinated with vaccinia the normal way, in their skin. Five negative controls were unvaccinated. Then at various intervals after vaccination, the monkeys received injections of live virus into their brains. The unvaccinated controls all died of meningitis from vaccinia multiplying in their brains; this was expected. The monkeys injected the soonest after vaccination died the same way, and the second-soonest survived a mild meningitis, but the rest proved immune and unharmed. None of them had encephalomyelitis though.

The authors weren’t satisfied with this, because the monkeys’ immune response was too quick somehow, so they tried again with more concentrated injections of virus. The results were pretty much the same though. Apparently vaccination protects the brain as much as other parts of the body, but even when the virus does get into a susceptible brain, it doesn’t cause encephalomyelitis, or at least not often enough to be detected in 21 monkeys (not very many).

The next hypothesis was that extracts from rabbit testicles might enhance the virus’s action, so they tried this with a few more monkeys. One got just testicle extract, but had no reaction. Another was vaccinated and then received extract, but also had no reaction. A couple more, one vaccinated and the other not, got virus combined with extract injected in their brains. They both had symptoms like stiff neck, lack of activity, etc, but when sacrificed and examined, their nervous system didn’t have the characteristic encephalomyelitis appearance. So testicle extract didn’t really seem to cause or enhance it either (at least not in 2-4 monkeys).

Next, the authors tested the hypothesis that injections of virus-free nervous material from rabbits, like in the rabies vaccine, could cause encephalomyelitis. So they made extracts or emulsions of rabbit brains and injected them into the muscles of eight monkeys, between 14 and 93 injections total, three per week (so over the course of up to 8 months). Five of these monkeys, including two with the fewest injections and two others with the most, had no symptoms or problems. One suddenly died after receiving 50 injections, for no apparent reason. But two had characteristic neurological and mobility problems, and their nervous tissue showed the loss of myelin and increased immune cell activity associated with encephalomyelitis. So that seemed like a positive result!

The four monkeys that hadn’t reacted to injections of brain at all were tested further with injections of vaccinia into their brains, after vaccination or not. The results here were the same as with those that hadn’t been injected with brain material, so the brain injections didn’t seem to affect the course of the vaccinia infection.

The two positive results in this study turned out to be a big deal, cited by almost 400 later papers and reviews; they were labeled “experimental allergic (or autoimmune) encephalomyelitis,” or EAE. This has been studied a lot as a (possibly controversial) model of multiple sclerosis. It was definitely decent evidence of the link between encephalomyelitis and brain-derived rabies vaccines though.

Here are some comments from later papers regarding this study:

 "Rivers and his associates were the first to succeed in producing, in the monkey, sterile, disseminated meningo-encephalomyelitis by often repeated injections of material from central nervous system tissue. Many of the observations made by these authors suggest that the disease induced was the result of an immunologic mechanism. Nevertheless, Rivers and his associates hesitated to express this view. Even 20 years later and after the accumulation of much new information—subsequent to the introduction of the use of adjuvants in the study of sterile experimental disseminated encephalomyelitis—conclusive evidence for its allergic nature is lacking."¹³

"Acute disseminated encephalomyelitis, which is essentially identical to the disease that occurs in patients receiving live or killed rabies virus vaccine, was produced in monkeys by Rivers and his colleagues in the 1930s by repeated injection of the animals with emulsions or extracts of normal nervous tissue from the central nervous system. These findings, together with increasing evidence that central nervous system tissue possesses organ-specific antigenic activity, provided strong evidence that the disseminated encephalomyelitis occurring in humans after rabies vaccination resulted from the host's immunologic responses. These responses, called forth by parenteral injections of nervous tissue, had the capacity to interact with antigenic components of the host's own central nervous system and thus to cause disease. It is important to note, however, that at about this same time there was increasing recognition that smallpox vaccination and some common exanthematous diseases of childhood such as rubeola were occasionally complicated by an acute encephalitic process. These cases of para- or postviral encephalitides had histopathological features that bore a striking similarity to those of the encephalomyelitis associated with rabies vaccine and the disseminated encephalomyelitis induced in monkeys by injections of nervous tissue."¹⁴

"Studies in the 1920s indicated that inoculation of rabbits with extracts of normal human spinal cord, or sheep brain, likewise resulted in occasional instances of post-vaccinal encephalomyelitis. The question was taken up by Thomas Rivers at the Rockefeller Institute, NY, perhaps because he himself had once been incapacited by progressive muscular atrophy and, being a virologist, he would be curious whether a virus could be implicated in post-vaccinal encephalomyelitis...Rivers concluded that the relation of the injections [of monkeys] to the central nervous system disease was 'not clear.'"¹⁵

"Experimental autoimmune encephalomyelitis is a well established model used to investigate the possible autoimmune etiology of multiple sclerosis. This model originated with Louis Pasteur's vaccinations with spinal cord from rabies-infected rabbits from 1885. This acute demyelinating disorder was later found to occur due to contamination of the inoculums by spinal cord components."¹⁶

Mackay and Anderson also provide a good overall history of Rivers’ and colleagues’ work¹⁷.

So overall, these were some legitimate problems with vaccines of old, though no longer. At the time, it was likely that, despite the risks, the vaccines were preferable to the diseases they prevented, on average. But for individual victims of encephalomyelitis, it probably was not worthwhile, so it’s good that those that study vaccines are constantly trying to improve them.

References:

1. Rivers, T. M., Sprunt, D. H. & Berry, G. P. Observations on Attempts to Produce Acute Disseminated Encephalomyelitis in Monkeys. J Exp Med 58, 39–53 (1933).

2. Encephalo-Myelitis Following Vaccination. The Lancet 208, 504–505 (1926).

3. Encephalo-Myelitis Following Vaccination. The Lancet 208, 764 (1926).

4. Turnbull, H. M. & McIntosh, J. Encephalo-Myelitis following Vaccination. Br J Exp Pathol 7, 181–222.19 (1926).

5. Turnbull, H. M. & Mcintosh, J. Encephalo-Myelitis Following Vaccination. The Lancet 211, 1094–1095 (1928).

6. Perdrau, J. R. Encephalo-Myelitis Following Vaccination. The Lancet 211, 1201 (1928).

7. Ward, G. Encephalomyelitis Following Vaccination. The Lancet 214, 1331–1332 (1929).

8. Jorge, R. Post-Vaccinal Encephalitis :: Its Association with Vaccination and with Post-Infectious and Acute Disseminated Encephalitis. The Lancet 219, 267–272 (1932).

9. Stuart, G. & Krikorian, K. S. A Fatal Neuro-Paralytic Accident of Antirabies Treatment. The Lancet 215, 1123–1125 (1930).

10. Wilson, S. A. K. A Lecture On Acute Cerebral Lesions At Different Ages. The British Medical Journal 1, 487–491 (1929).

11. Sampson, J. H., Archer, G. E., Mitchell, D. A., Heimberger, A. B. & Bigner, D. D. Tumor-specific immunotherapy targeting the EGFRvIII mutation in patients with malignant glioma. Seminars in Immunology 20, 267–275 (2008).

12. Glück, R., Matthieu, J. M., Wegmann, A. & Méan, F. Absence of myelin basic protein in an improved purified duck embryo rabies vaccine. Neurochem Pathol 4, 69–75 (1986).

13. Lipton, M. M., Freund, J. & Brady, E. The Transfer of Experimental Allergic Encephalomyelitis in the Rat by Means of Parabiosis. J Immunol 71, 380–384 (1953).

14. Paterson, P. Y. Neuroimmunologic Diseases of Animals and Humans. Reviews of Infectious Diseases 1, 468–482 (1979).

15. Mackay, I. R. Travels and travails of autoimmunity: A historical journey from discovery to rediscovery. Autoimmunity Reviews 9, A251–A258 (2010).

16. Mecha, M., Carrillo-Salinas, F. J., Mestre, L., Feliú, A. & Guaza, C. Viral models of multiple sclerosis: Neurodegeneration and demyelination in mice infected with Theiler’s virus. Progress in Neurobiology 101–102, 46–64 (2013).

17. Mackay, I. R. & Anderson, W. H. What’s in a name? Experimental encephalomyelitis: ‘Allergic’ or ‘autoimmune’. Journal of Neuroimmunology 223, 1–4 (2010).