Fatores de virulencia em fungos

INTRODUCTION

Mycologists estimate that there are 100,000 species of fungi in nature. These fungi inhabit different niches, a number of them are symbiotic and may live in commensalism, mutualism or parasitism with other organisms. However, only some of the fungal species are pathogenic to man, a fact that has led to several studies providing a better understanding of the relationship among parasite, host and virulence factors 14,93.
The symbiotic-parasitic relationship produces an infectious process leading to lesions of the host tissues and establishment of disease due to a direct imbalance in parasite-host interaction. The host provides conditions for growth that usually differ markedly from the ecological niche that the fungus normally inhabits. In order to survive in this new environment, potential pathogens must withstand high temperatures, hormonal influences and attacks by phagocytes cells of the immune system 93 (Figure 1).

Fig. 1 - Factors that affect the transition from the saprophytic to parasite form in host-fungus relationship.

This process of adaptation to a more resistant form to the new microenvironment frequently results in aggression to host tissues.
Some fungi, such as dimorphic fungi, have a greater ability to grow in adverse conditions provided by the host, and to produce disease. This process called pathogenicity is considered to be the result of direct interaction between the pathogen and host.
Several fungal factors may help in this relationship and are frequently studied being known as virulence factors 14,38.
For an organism to cause disease it must (1) enter the host, (2) multiply in host tissues, (3) resist or not stimulate host defense mechanisms, and (4) damage the host. The success of all these processes will depend on which virulence factor the fungus uses 14.
Some virulence factors are of obvious importance. For example, the ability of a fungus to grow at 37ºC is a virulence factor for
invasive