untitled

acquired during continuous or periodic exposure to the

pathogen. The reactivation of long-term latent infec-

tion cannot be ruled out, because theoretically even a

single latent Pneumocystiscell could give rise to infec-

tion when a host is immunocompromised. But studies

of population genetics have helped to address this

issue, by comparing the strains found in adult patients

who have remained close to their birthplace against the

strains found in patients who moved far away from

their birthplace. The data indicate that adult patients

acquire strains that are more similar to those in their

current place of residence than in their birthplace,

strongly suggesting that infection is reacquired rather

than being carried since early childhood.

The following points can be made in summary of the

current knowledge of Pneumocystis:

• Pneumocystisis a genus of worldwide distribution.
  It exists as many different host-specific species, with
  no evidence of cross-infection between different
  hosts.


• Pneumocystisseems to be a primitive fungus-like
  organism that represents one of the earliest basal
  lineages of fungi and has diversified as an obligate
  parasite that infects many species of mammals,
  including humans.


• In human populations, young children are fre-
  quently infected but typically exhibit only a transient
  infection and subsequently develop immunity.
  Children may be the primary reservoir of infection.


• Adults seem to acquire infection from environmen-
  tal sources close to their areas of residence, but they
  only develop disease if they are immunosuppressed
  or immunocompromised. In these circumstances
  the infection can progress rapidly, and is closely
  correlated with a low count of circulating CD4+T
  lymphocytes.

We return to this and other fungal pathogens of

humans in Chapter 17, where we consider the methods

available for treating human mycoses.

Online resources

Aspergillus fumigatus genome sequence. http://

http://www.tigr.org/tdb/e2k1/afu1

Centers for Disease Control and Prevention, USA, Image

library. http://www.dpd.cdc.gov/dpdx/HTML/

ImageLibrary/Pneumocystis_il.htm

Doctor Fungus website. http://www.doctorfungus.org. [An

excellent, comprehensive source of up-to-date informa-

tion on all the human mycoses]

General texts

Evans, E.G.V. & Richardson, M.D., eds (1989) Medical

Mycology: a practical approach. Oxford University Press,

Oxford.

Kwon-Chung, K.J. & Bennett, J.E. (1992) Medical Mycology.

Lea & Febinger, Philadelphia.

Sutton, D.A., Fothergill, A.W. & Rinaldi, M.G., eds (1998)

Guide to Clinically Significant Fungi. Williams & Wilkins,

Baltimore.

Cited references

Borges-Walmsley, M.I., Chen, D., Shu, X. & Walmsley, A.R.

(2002) The pathobiology of Paracoccidioides brasiliensis.

Trends in Microbiology 10 , 80 – 87.

Brandhorst, T.T., Rooney, P.J., Sullivan, T.D. & Klein, B.S.

(2002) Using new genetic tools to study the patho-

genesis of Blastomyces dermatitidis. Trends in Microbiology

10 , 25–30.

Brouta, F., Descamps, F., Monod, M., Vermout, S., Losson,

B. & Mignon, B. (2002) Secreted metalloprotease gene

family of Microsporum canis. Infection & Immunity 70 ,

5676–5683.

Brown, A.J.P. & Gow, N.A.R. (2001) Signal transduction and

morphogenesis in Candida albicans. In: The Mycota VIII.

Biology of the Fungal Cell(Howard, R.J. & Gow, N.A.R.,

eds), pp. 55–71. Springer-Verlag, Berlin.

Calderone, R.A. & Fonzi, W.A. (2001) Virulence factors of

Candida albicans. Trends in Microbiology 9 , 327–335.

Domer, J.E. & Kobayashi, G.S., eds (2004) The Mycota XII.

Human Fungal Pathogens. Springer-Verlag, Berlin.

Douglas, L.J. (2003) Candidabiofilms and their role in infec-

tion. Trends in Microbiology 11 , 30–36.

Kwon-Chung, K.J. & Bennett, J.E. (1992) Medical Mycology.

Lea & Febinger, Philadelphia.

Magrini, V. & Goldman, W.E. (2001) Molecular mycology:

a genetic toolbox for Histoplasma capsulatum. Trends in

Microbiology 9 , 541–546.

Perfect, J.R. (2004) Genetic requirements for virulence

in Cryptococcus neoformans. In: The Mycota XII. Human

Fungal Pathogens(Domer, J.E. & Kobayashi, G.S., eds),

pp. 89–112. Springer-Verlag, Berlin.

Silva-Vergara, M.L., Martinez, R., Camargo, Z.P., Malta, M.H.,

Maffei, C. M. & Chadu, J.B. (2000) Isolation of

Paracoccidioides brasiliensis from armadillos (Dasypus

novemcinctus) in an area where the fungus was recently

isolated from soil. Medical Mycology 38 , 193–199.

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