There appears to be a connection between the distribution of histoplasma and the prevalence of PD in South America.

"Histoplasmosis is a cosmopolitan mycosis with areas of particularly high endemicity. In North America, the endemic regions are in the Midwestern and Southeastern of United States ... In Latin America, the most prevalent areas are in Venezuela, Ecuador, Brazil, Paraguay, Uruguay and Argentina ... (Fig. 2)." [1]

The figure shows endemic areas around the north and east coasts of South America and along the Amazon. All this detail would be very interesting if only we had detailed maps showing the distribution of PD within these countries. Unfortunately, we have, at best, national statistics. Most countries have zones within and without the endemic area. The exception is Uruguay which is entirely within the endemic area.

If histoplasma is a driver of PD, we would expect a higher prevalence of PD in those areas in which a higher proportion of the population are in the endemic area.

Parkinson's prevalence statistics are difficult to get, but many point to Uruguay as being a hot spot, e.g. a crude prevalence rate of 405 per 100,000 of population [2].

References

[1] "Diagnosis of histoplasmosis"
Allan Jefferson GuimarãesI,II; Joshua D. NosanchukII; Rosely Maria Zancopé-OliveiraI
Braz. J. Microbiol. vol.37 no.1 São Paulo Jan./Mar. 2006
http://www.scielo.br/scielo.php?pid=...pt=sci_arttext

[2] "The challenge of Parkinson's disease management in Africa"
Age and againg, vol 36.2, pp 122-127
C. L. Dotchin, O. Msuya and R. W. Walker
http://ageing.oxfordjournals.org/content/36/2/122.full

John