Interview with an expert

Spiroplasma may cause Creutzfeldt-Jakob Disease.  An interview with a leading expert in infectious diseases: Dr. Frank Bastian.

What is Creutzfeldt-Jakob Disease (CJD?)

CJD is a transmissible disease characterized by spongy degeneration of the brain. It strikes about one in 1 million people annually. About 5% of CJD cases occur in families or among certain ethnic groups. The disease has been transmitted inadvertently during medical treatment and surgical procedures. CJD has been transmitted by the administration of growth hormone derived from the pituitary glands of people who died from CJD. The disease also has been transmitted by transplantation of corneas and dura tissue obtained from people who died from CJD. CJD has been transmitted experimentally to monkeys by oral feeding of contaminated tissue and to lab animals by infusion of white cells.

CJD symptoms usually appear when people are in their 40s, 50s, and 60s. Ninety percent of people with CJD die within a year of the onset of signs and symptoms. Most die in four to six months.

CJD is difficult to diagnose early. At first, people experience psychological disturbances and bizarre behavior, and then proceed to dementia, memory loss, stiffening of muscles, and difficulty walking. Although this illness may be confused with Alzheimer's disease, people with Alzheimer's usually do not develop neurologic signs. The clinical diagnosis is usually in error at least 25% to 30% of the time.

Researchers suspect that 10 people in Britain who contracted a CJD-like illness were infected by cows afflicted with bovine spongiform encephalopathy. How do these British cases compare with classic CJD?

Researchers showed that the CJD-like illness in Britain had a different clinical course than classic CJD. All of the British cases occurred in people younger than 42 years; in fact, three cases occurred in teenagers. Moreover, the duration of illness exceeded a year in five of the 10 cases. The CJD-illness also had a pathology different from CJD. For example, the CJD variant is characterized by extensive amyloid plaque formation and by degeneration of the cerebellum.

You postulate that Spiroplasma bacteria causes CJD. Please describe them.

Spiroplasmas are similar to mycoplasmas in that they do not have a cell wall and have among the smallest genomes of any living organisms. Spiroplasmas, which were only discovered in 1976, are present in the hemolymph of almost all insects. There probably are several million strains of spiroplasmas. They are very fastidious organisms. Many spiroplasmas grow at fairly low temperatures. A few strains grow at 37° C, human body temperature. Many spiroplasmas cause diseases in plants. Spiroplasmas usually are associated with a vector. For example, a leaf hopper carries a spiroplasma that infects orange trees. These organisms are essentially resistant to all bacteriocidal antibiotics.

How did you connect spiroplasmas with CJD?

In 1976, I examined a brain biopsy from a patient with CJD using electron microscopy. I saw a spiral structure foreign to the tissue. It had features of the newly reported spiroplasmas. In 1981, a team in New York reported finding a fibril protein in scrapie-infected brain tissue. This scrapie-associated fibril (SAF) protein was 4 nm in diameter and 200 nm long. In 1983, the team looked at various tissues of CJD and kuru and demonstrated scrapie-associated fibrils consistently in these diseases but not in control tissues. These SAF are identical morphologically to the internal fibrils of spiroplasmas. This similarity, in my mind, as a pathologist, solidifies the link between spiroplasmas and CJD.

Moreover, antibodies to SAF react with internal fibrillar proteins from Spiroplasma and digested brain material from people with CJD, suggesting that these proteins essentially are the same. I have shown in my laboratory that spiroplasmas are neurotropic. If you inoculate them peripherally into suckling rats, they will eventually localize to the brain tissues. The organisms will produce a persistent infection and produce a spongy change in the brain tissue of these animals. The neuropathologic changes are similar to those seen in CJD.

Another piece of circumstantial evidence is that spiroplasmas are within the size range of the agent that transmits CJD and other transmissible spongiform encephalopathies. Spiroplasmas will pass through a 50 nm-pore filter. The transmissible agent's size has been determined to be 42 nm.

What would prove that Spiroplasma causes CJD and related illnesses?

Definitive evidence of this link would be to demonstrate that spiroplasma DNA occurs in the brain tissue of people with CJD and related illnesses, but not in brain tissue from controls. This could be done by using polymerase chain reaction assays to detect nucleotide sequences in genes unique to spiroplasmas and common to all types of spiroplasmas. I have 15 types of spiroplasmas in my laboratory and am in the process of looking for nucleotide sequences common to all of them.

Why have investigators failed to find a causative agent despite 30 years of looking?

The obvious way to look for an agent directly is by electron microscopy, but this method may not be appropriate for spiroplasmas. Spiroplasmas are similar to mycoplasmas, and it is a well-known phenomenon that mycoplasmas are able to blend with cell membranes. What happens, possibly, is that spiroplasmas essentially fuse with host-cell organelle membranes, thereby blending with the background, so you would not see it unless you had a marker to label it. Developing such as marker has been difficult because spiroplasmas are difficult to cultivate. No more than half of the known strains are culturable.

After inoculating spiroplasma in suckling rats, we examined brain tissues by electron microscopy early in the infection and could document the organisms in the tissues. They appeared as membrane-bound forms, except for the one instance in which I observed the spiral form. Later in infection, when we knew that the tissues were infectious by broth culture, we couldn't find any evidence of the organism by looking at the tissues extensively with electron microscopy.

What do you make of the prion theory?

The prion is a red herring. Prions are thought to be self-replicating proteins. Some researchers believe prions are the cause of CJD and related illnesses because they have found prions in brain tissue from people with CJD and sheep with scrapie but not in normal brain tissue. A shortcoming in the prion theory is that CJD and scrapie can be transmitted without prions. Brain material from which the prion has been removed with antibodies can still infect animals. Moreover, the prion has been found in unrelated disease processes, such as Kawsaski syndrome and inclusion body myositis.

The protein that some researchers believe causes CJD and related illnesses is a reconfigured normal host protein. Studies have shown that if you take the gene for the normal protein out of the mouse, the mouse does not develop spongiform encephalopathy when injected with infectious material. The protein is likely important in the pathogenesis of the disease. Researchers have jumped to conclusions from that evidence to suggest that the protein has to be the causative agent, and they have not considered any other possibility. It is quite possible that spiroplasmas may be inducing the formation of this prion protein to protect itself from the immune system.

The immune system is very important in the pathogenesis of CJD. We know that the agent replicates in the spleen and lymph nodes and occasionally causes an immunologic reaction. Auto-antibodies are characteristically seen in the late stages of experimental and naturally occurring disease.

A common phenomenon among the mycoplasmas is that the organisms bind host proteins that often are of identical molecular weight to their surface proteins and, therefore, are looked at by the immune system as being the same as the host. The spiralin protein on the surface of spiroplasmas shows a migration pattern on gel electrophoresis with a molecular weight of 27,000 Da to 30,000 Da, similar to that of the so-called prion protein. This biochemical similarity is compatible with spiroplasma etiology.

If spiroplasmas turn out to be the cause of CJD and related illnesses, could antibiotics be used to treat them?

Spiroplasmas are susceptible to erythromycin and tetracycline, but these drugs would not be of value in treating CJD or related illnesses because the drugs are bacteriostatic, not bacteriocidal. I would hope that one of the newer quinolones would be useful in killing the organism.

Why might humans have contracted a CJD variant from cows with bovine spongiform encephalopathy (BSE)?

The transmission from cows to humans might be related to an increase in virulence in the BSE agent. It is known that a pathogen's virulence can be increased by passing a strain of the agent through a series of hosts of the same species. Experiments with scrapie have shown that such serial passage of the scrapie agent can increase the virulence and cut the incubation time in half.

In Britain, sheep and cattle tissue used to be ground up and added to cattle feed. Cows may have initially contracted BSE by eating feed containing scrapie-infected tissue. Eventually, infected cattle tissue was fed to cattle, so the infectious agent was passed through one cow to another. This may have increased the virulence of the infectious agent to the point where it could infect humans.