by Professor Elsheikh Mahgoub, Faculty of Medicine, Jordan University of Science & Technology, Irbid, Jordan (Formerly of Faculty of Medicine, Khartoum, Sudan ).
Perhaps it is important, in this article, to reflect first, on the diseases caused by the genus Aspergillus as outlined by Denning ( 2000)[1] which could be summarized as follows :
This article will solely discuss the role of A.nidulans and A.flavus as causative agents of this latter condition.
The term Mycetoma is preferred to the old term madura foot which was derived from the early cases when the foot was affected in almost all patients seen when the disease was discovered in India and fully reported by Carter (1874)[2] .
"Mycetoma is a chronic, progressive, fungal tumour of skin and subcutaneous tissues and will ultimately attack bone as well.Development is slow, pain is not a marked feature and sinuses discharge at the skin surface. From these sinuses discharge little grains or granules of various colours, the grains being colonies of the causal organisms and the colour dependent on the species".
A.nidulans :
According to Nicolle and Blanc (1920) [4], the first report
of isolating A.nidulans from a patient with mycetoma was
in 1906 by Pinoy from Tunisia [5]. No other report was made till
Baylet et al (1968) [6] isolated A.nidulans from
a patient with mycetoma of the knee in Senegal. In 1971 a fully
documented case of maduromycetoma (eumycetoma) of the foot caused
by A.nidulans was reported from Sudan by Mahgoub [7].
Three more cases due to A.nidulans were also seen in Sudan
since then.
A.flavus :
The first authentic case of mycetoma caused by A.flavus
was reported by Mahgoub (1973)[8] when the fungus was isolated from
the foot of a Sudanese patient, confirmed by presence of grains in
histological sections and demonstration of antibodies to it in his
blood. This was confirmed by the report of mycetoma of the back due
to A.flavus in an American patient successfully treated
with itraconazole by Witzig, Greer and Hyslop (1996)[9] .
The clinical picture of mycetoma due to aspergilli is not
different from that caused by eumycetoma due to known fungi. It
occurs on the foot in most cases (Figs.1 & 2) and other sites
as in the American case [9]. However there were two unusual phenoma
in the Sudanese cases. The lesion caused by
A.nidulans showed more bleeding than usually seen in
mycetoma and that caused by A.flavus was more painful than
what usually reported by mycetoma patients.
All cases had a long standing history and lesions showed sinuses
through which yellowish white grains were discharged.
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Figure1: Mycetoma of the right foot due to A.nidulans.
Figure2: Mycetoma of the right foot due to A.flavus.
Grains from both A.nidulans and A.flavus mycetomas grow well on routine bacteriological media but identification is made from cultures onto 2% glucose peptone agar (Sabourauds). A.nidulans is characteristically identified by the presence of perithecia and Hulle cells (Fig.3) in aging cultures and A.flavus by the greenish yellow colour of colonies and its rough conidiophores.
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Figure 3: Aspergillus head and Hulle cells of A.nidulans in lactophenol cotton blue.
No special stain is needed because grains are quite visible in sections stained with the routine haematoxylin and eosin (H/E ).They take a light eosinophilic stain and usually seen in the middle of polymorphonuclear leucocytes. Grains may be circular or oval in shape, composed of compact hyphae with or without spores and may be partly vesicular (Fig.4).They measure about 150 x 70 m. Special stains e.g periodic acid schiff and silver reveal the details of colonies showing individual segmented hyphae.
Figure 4: Vesicular pale grain of A.flavus in histological section, H/E stain x 800.
Serology:
Both circulating antibodies and antigens have been demonstrated
using counterimmunoelectrophoresis and ELISA [8 and 9] and can
therefore be made use of in diagnosis and monitoring treatment.
Treatment :
Aspergilli in general and A.flavus in particular have shown good response to itraconazole, Gumaa et al (1992 )[10]; Witzig et al (1996 ) [9]. However treatment of mycetoma has to be continued for periods between six months and one year.This can be shortened if the lesion allows bulk reduction surgery, but amputation in mycetoma pedis should be avoided.
Treatment is well monitored by assessing the level of antibodies to or antigens of the causative organism or both [8 and 9]
References (in separate window)