Geographical and seasonal correlation of multiple sclerosis to sporadic schizophrenia

Abstract

BACKGROUND: Clusters by season and locality reveal a striking epidemiological overlap between sporadic schizophrenia and multiple sclerosis (MS). As the birth excesses of those individuals who later in life develop schizophrenia mirror the seasonal distribution of Ixodid ticks, a meta analysis has been performed between all neuropsychiatric birth excesses including MS and the epidemiology of spirochaetal infectious diseases. RESULTS: The prevalence of MS and schizophrenic birth excesses entirely spares the tropical belt where human treponematoses are endemic, whereas in more temperate climates infection rates of Borrelia garinii in ticks collected from seabirds match the global geographic distribution of MS. If the seasonal fluctuations of Lyme borreliosis in Europe are taken into account, the birth excesses of MS and those of schizophrenia are nine months apart, reflecting the activity of Ixodes ricinus at the time of embryonic implantation and birth. In America, this nine months' shift between MS and schizophrenic births is also reflected by the periodicity of Borrelia burgdorferi transmitting Ixodes pacificus ticks along the West Coast and the periodicity of Ixodes scapularis along the East Coast. With respect to Ixodid tick activity, amongst the neuropsychiatric birth excesses only amyotrophic lateral sclerosis (ALS) shows a similar seasonal trend. CONCLUSION: It cannot be excluded at present that maternal infection by Borrelia burgdorferi poses a risk to the unborn. The seasonal and geographical overlap between schizophrenia, MS and neuroborreliosis rather emphasises a causal relation that derives from exposure to a flagellar virulence factor at conception and delivery. It is hoped that the pathogenic correlation of spirochaetal virulence to temperature and heat shock proteins (HSP) might encourage a new direction of research in molecular epidemiology.

Figure 1

Geographical correlation of schizophrenic birth excesses and MS prevalence to spirochaetal diseases The gradient of MS prevalence [15] and schizophrenic birth excesses [16,28] entirely spares the tropical belt where human treponematoses prevail [27]. In subtropical zones between the 37° latitudes, there exists an additional climatic effect diminishing the prevalence rates of MS worldwide. This 'rule' of variation by latitude, however, is violated in Europe, Australia and New Zealand where circumpolar migratory seabirds reportedly introduce Ixodes uriae and Borrelia garinii [29] from the MS hot spots in the north [12,15]. The arrows represent the migratory routes and distribution of seabirds if a number of species such as puffins (shearwaters), seagulls and terns are taken together [56-59]. The sites from where samples in search for Borrelia garinii were collected by Olsen et al. [29] are marked with a red dot and include the Egg and St. Lazaria Islands (Alaska), Gannet Island in Newfoundland (Canada), Iceland, the Falklands, the Faroes, Bonden Island (Sweden), Cape Sizun (France), the Crozet Islands (South Africa), and Campbell Island (New Zealand). There are just a few subtropical areas including Madeira, Morocco and Tunisia from where the presence of B. burgdorferi s.l. has been documented. Two protective factors could thus explain the rarity of MS and schizophrenic birth excesses in developing countries: acquired immunologic resistance against spirochaetes in the tropics, and higher temperature being inversely related to tick-borne spirochaetal transmission in subtropical zones.

Figure2

Seasonal correlation of neuropsychiatric birth excesses to Ixodes ticks and Lyme borreliosis in America and Europe In America, the seasonal distribution of schizophrenic [48] and MS [47] birth excesses exactly mirrors the periodicity of Ixodes scapularis along the East Coast [37] and that of Ixodes pacificus along the West Coast [49]. Curiously enough, in many studies conducted in the USA, the month of June is often the month with the lowest risk of developing schizophrenia (Jean-Paul Selten, personal communication, 2002). This schizophrenic birth deficit corresponds to the tick activity, which is at its lowest nine months earlier in September, being particularly striking, if both species Ixodes scapularis and Ixodes pacificus are taken together. If stochastic annual fluctuations are taken into consideration [43,44], the spring (a) population of Ixodes ricinus [37] likewise mirrors the significant birth excess rates of schizophrenia [45], ALS [51] and MS [8] in Europe. The nine months' shift between sporadic schizophrenia on the one hand and ALS and MS on the other reflects the possible transplacental transmission of Borrelia burgdorferi [23] at the time of conception [16] and delivery [24].