For more than a century many strands of evidence have pointed toward an infectious cause for MS.
Pierre Marie, lecturing in 1892, said that “the causative agent in multiple sclerosis is manifestly of an infective nature. What is its precise nature? No one so far has been able to isolate it but one day this goal will be achieved.” 
For a long time, little progress was made. In the 1950s, however, Paul Le Gac noticed similarities between multiple sclerosis and symptoms developed in the aftermath of diseases like Rocky Mountain spotted fever and typhus caused by Rickettsia bacteria.  Rickettsia are obligate intracellular parasites that cannot survive outside a host. By 1966, Le Gac recognized that the Chlamydiae, another order of intracellular parasitic bacteria, might be responsible for MS. 
Le Gac tried treating multiple sclerosis with tetracyclines and other broad spectrum antibiotics, and reported a number of cures. Here is one of his case studies:
Mr. Maurice Q., a Belgian citizen, 46 years of age. Multiple sclerosis was manifested in 1955 by transient retrobulbar neuritis. In 1956 he became bedridden. As of November 1961, [he had been] totally quadriplegic for three years….
Antibiotic treatment and alginated baths were followed, within a few months, by a spectacular improvement.
In May 1962, Mr. Q. was walking normally. He was able to discard all assistive devices, and soon afterward went back to work as a freight–truck driver. 
However, Le Gac’s work was criticized on the ground that MS patients generally lacked antibodies to Rickettsia, not all MS patients responded to Le Gac’s treatment, and no controlled clinical trials had been conducted. 
Meanwhile, epidemiological evidence was accruing in support of the idea of an infectious origin. For instance, MS was virtually unknown in the Faeroe Islands until British troops were stationed there in 1940, after which an epidemic of MS occurred. Nearly all the MS cases diagnosed between 1943 and 1960 were in people who had resided as children in the towns where the British were stationed.  In general, MS risk is increased in populations with low vitamin D and poor hygiene; both associations are suggestive of an infectious origin, since vitamin D is so crucial for intracellular immunity. 
Technological advances in molecular biology in the 1980s and 1990s finally made possible a robust investigation into microbial causes. A key invention was real-time PCR, which was honored by the Nobel Prize for Chemistry in 1993. This technique permitted sensitive detection of bacterial DNA from tissue or fluid samples, and enabled for the first time reliable detection (and species identification) of intracellular bacteria. PCR entered research use in the 1990s.
Some scientists at Vanderbilt, who had previously been studying the role of Chlamydia pneumoniae in chronic fatigue, discovered its presence in the cerebrospinal fluid of MS patients.  PCR showed that DNA from C. pneumoniae was present in the cerebrospinal fluid of up to 97% of MS patients.  In 2002, the Vanderbilt scientists patented a combination-antibiotic therapy for C. pneumoniae . They established a clinic at Vanderbilt specializing in antibiotic treatment of chronic fatigue syndrome and MS.
In medicine, some of the most important progress has been made by doctors and scientists trying to cure their own conditions. The combination of high motivation, intimate familiarity with the disease, and technical expertise is hard to beat. For this reason, I think the story of Dr. David Wheldon, a clinical microbiologist from Britain, and his wife Sarah is significant in the history of MS. I will abridge their story from various accounts they have published. [10, 11, 12, 13]
In 1999, the Wheldons contracted a respiratory infection which produced a mild pneumonia. In its aftermath, Sarah developed asthma and David developed a myalgia which prevented him from turning his head. By 2003, Sarah had developed full-blown multiple sclerosis: she could not walk unaided, her speech was slurred, she was numb from the waist down, and an MRI revealed numerous white-matter brain lesions.
Dr. Wheldon searched the literature and found the Vanderbilt work. He gave his wife doxycycline and roxithromycin, both effective anti-chlamydial agents. He writes:
What followed was dramatic. For a few days, Sarah had a Herxheimer-like reaction, with a fever and night-sweats. After this, her mental fog and cognitive deficits speedily began to vanish. Slowly, the disease was rolled back … 
Sarah improved from a grade of 7 on the Kurtzke Expanded Disability Status Scale (EDSS) to a grade of 2, and remains at that grade seven years later. The same antibiotics cured David’s myalgia.
Dr. Wheldon and Dr. Stratton of the Vanderbilt group have since collaborated on papers summarizing the evidence for C. pneumoniae as the causal agent of MS.  Dr. Wheldon now treats MS patients, and he and his wife also helped popularize a site, cpnhelp.org, set up by a chronic fatigue and fibromyalgia patient, Jim Kepner, to help chronic disease suffers defeat C. pneumoniae infections. This site has a rich lode of MS patients recounting their experiences with antibiotics.
On the clinical research side, pilot trials of antibiotic therapies for MS have been undertaken by several groups, with promising results. [15, 16, 17] It seems only a matter of time, patient pressure, and perhaps a few funerals before large-scale trials are funded.
The experience of MS patients shows that combination antibiotic treatments targeted at C. pneumoniae often halt MS progression and sometimes, as in the case of Sarah Wheldon, bring about substantial recovery.
In an upcoming post, I’ll talk about dietary reasons why antibiotics may fail, or succeed only after a protracted struggle with exceptionally difficult side effects.
 Marie, P., Leçons sur les Meladies de la Moelle, Paris, Masson, 1892. Cited in: “Cures” for multiple sclerosis. Br Med J. 1970 Jan 10;1(5688):59-60. http://pmid.us/5411441.
 “Cures” for multiple sclerosis. Br Med J. 1970 Jan 10;1(5688):59-60. http://pmid.us/5411441.
 Le Gac P et al. The psittacosis virus in the etiology of multiple sclerosis. C R Acad Sci Hebd Seances Acad Sci D. 1966 Nov 28;263(22):1793-5. http://pmid.us/4963916. A translation of the full text is available here: http://www.davidwheldon.co.uk/Le%20Gac%204.pdf. More case studies may be found here: http://www.davidwheldon.co.uk/Le%20Gac%206.pdf.
 Field EJ, Chambers M. Rickettsial antibodies in multiple sclerosis. Br Med J. 1970 Jan 3;1(5687):30-2. http://pmid.us/4983591.
 Kurtzke JF, Hyllested K. Multiple sclerosis in the Faroe Islands: I. Clinical and epidemiological features. Ann Neurol. 1979 Jan;5(1):6-21. http://pmid.us/371519. Kurtzke JF, Heltberg A. Multiple sclerosis in the Faroe Islands: an epitome. J Clin Epidemiol. 2001 Jan;54(1):1-22. http://pmid.us/11165464.
 Cantorna MT. Vitamin D and multiple sclerosis: an update. Nutr Rev. 2008 Oct;66(10 Suppl 2):S135-8. http://pmid.us/18844840.
 Sriram S et al. Multiple sclerosis associated with Chlamydia pneumoniae infection of the CNS. Neurology. 1998 Feb;50(2):571-2. http://pmid.us/9484408. Stratton CW et al. Does Chlamydia pneumoniae play a role in the pathogenesis of multiple sclerosis? J Med Microbiol. 2000 Jan;49(1):1-3. http://pmid.us/10628821.
 Sriram S et al. Chlamydia pneumoniae infection of the central nervous system in multiple sclerosis. Ann Neurol. 1999 Jul;46(1):6-14. http://pmid.us/10401775.
 Mitchell, William M. & Stratton, Charles W. “Diagnosis and management of infection caused by Chlamydia,” U.S. Patent Number 6,884,784, http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=1&f=G&l=50&co1=AND&d=PTXT&s1=6884784.PN.&OS=PN/6884784&RS=PN/6884784.
 David’s story told by himself: http://www.cpnhelp.org/?q=david_wheldons_story_cpn_treatment_of_cardiac_myalgic_symptoms
 Sarah’s story told by herself: http://www.cpnhelp.org/?q=node/4
 Sarah’s story told by David: http://avenues-of-sight.com/Ignoring-the-Evidence.html
 Stratton CW, Wheldon DB. Multiple sclerosis: an infectious syndrome involving Chlamydophila pneumoniae. Trends Microbiol. 2006 Nov;14(11):474-9. http://pmid.us/16996738. Stratton CW, Wheldon DB. Antimicrobial treatment of multiple sclerosis. Infection. 2007 Oct;35(5):383-5; author reply 386. http://pmid.us/17882356.
 Sriram S et al. Pilot study to examine the effect of antibiotic therapy on MRI outcomes in RRMS. J Neurol Sci. 2005 Jul 15;234(1-2):87-91. http://pmid.us/15935383.
 Minagar A et al. Combination therapy with interferon beta-1a and doxycycline in multiple sclerosis: an open-label trial. Arch Neurol. 2008 Feb;65(2):199-204. http://pmid.us/18071030.
 Metz LM et al. Glatiramer acetate in combination with minocycline in patients with relapsing–remitting multiple sclerosis: results of a Canadian, multicenter, double-blind, placebo-controlled trial. Mult Scler. 2009 Oct;15(10):1183-94. http://pmid.us/19776092.