Fungal disease agents are widespread and can be isolated from a wide range of animals, from the soil and the environment. This makes fungal diseases a group of transmissible infections in which animals can represent important reservoirs and asymptomatic carriers for people in close contact with them. The important role of farm and pet animals as carriers and spreaders is well known. Fungal infections in animals and immunocompetent individuals are commonly associated with asymptomatic infections or mild and transient local skin or mucosal lesions, but they can represent important risk factors in HIV infected or AIDS affected patients, due to the impairment of their immune systems (Durden and Elewski, 1997).
Cryptococcus neoformans is an ubiquitous encapsulated yeast. The microorganism has a gelatinous capsule and measures 4 to 12 µm. It is frequently found in soil and pigeon excreta. There are four cryptococcal serotypes, types A and D belong to Cryptococcus neoformans var. neoformans and types B and C belong to Cryptococcus neoformans var. gattii. Of those, type A is the most common cause of cryptococcal disease in HIV infected and AIDS affected patients (Stevens, 1990).
C. neoformans is commonly found in pigeon droppings and less frequently in soil (Levitz, 1991). Bird droppings provide an enriched media for the yeast. Wild birds, especially pigeons are frequently infected with these organisms but they usually become asymptomatic carriers and do not themselves become sick. Other animals, especially cats, may develop cutaneous infections, but these are not considered a public health hazard because the organism does not aerosolize from these sites. Transmission of the yeasts to humans occurs by inhalation of airborne organisms. However, even in highly contaminated areas, only a small number of organisms of the appropriate size to reach the alveoli are aerosolized.
Cryptococcus neoformans is a common infectious agent found in the accounting of HIV infected or AIDS affected patients. Occurring in 5-10 percent of patients, it is considered the most common life-threatening fungal infection in the AIDS affected population and it represent a frequent cause among all opportunistic infections in HIV infected individuals (Kirkpatrick, 1990).
Infections in most immunocompetent individuals are subclinical, but in HIV infected or AIDS affected patients, over half develop widespread cryptococcal dissemination rather than localized disease. Neurological findings are common, and occur in 75 percent of HIV infected patients with cryptococcosis.
Skin lesions occur in up to 10 percent of all patients with disseminated cryptococcosis, and include subcutaneous nodules, herpetiform lesions, Kaposis sarcoma-like lesions, and molluscum contagiosum-like lesions. Skin lesions permit easy access to tissue for biopsy and diagnosis. Oral and rectal lesions may also occur.
Histoplasma capsulatum var. capsulatum is a dimorphic fungus. It grows as an intracellular yeast in the host and as a mould in the laboratory or environment. The organism is prevalent in soil enriched with guano in caves, old buildings, school playgrounds, farms and parks. Infection occurs through the inhalation of arthroconidia that invade alveolar macrophages and induce a dissemination of infection. Risk factors are all occupations or activities involving exposure to chickens, starlings and bats (Wheat, 1988).
Clinical presentations of infection are characterized by fever, weight loss, hepatomegaly, splenomegaly, enteritis, chorioretinitis, endocarditis, skin lesions, meningitis and cough. Fulminant disease with multiorgan failure and rapid death can occur. Skin and mucous membrane lesions are non-specific and include keratotic papules, nodules, ulcers, abscesses, plaques, pustules, erythema nodosum and herpetiform lesions. Petechiae secondary to thrombocytopenia may be present. Chronic mucosal ulceration, particularly on the tongue, palate, rectum and buccal mucosa are common (Minamoto and Armstrong, 1988).
Candida spp. account for one of the most common fungal infections in humans in general and are the most common cause of fungal infections in HIV infected or AIDS affected patients. The most common species is Candida albicans, but other species, including C. tropicalis, C. krusei, and Torulopsis (Candida) glabrata, are frequently found in human infections.
In HIV infected or AIDS affected patients, due to the intact humoral immune response, mucous membrane infections rather than disseminated candidiasis occur. Mucocutaneous candidiasis in HIV infected persons is often associated with an early progression to AIDS (Kirkpatrick, 1990).
The oral carriage rate of Candida spp. approaches 100 percent in patients with HIV (Stevens, 1990). Oral candidiasis occurs in approximately 45 percent of patients with AIDS (Daar and Meyer, 1992) and often occurs when the CD4 T cell count falls below 250 cells/microlitre. Of those, more than 50 percent will develop AIDS within 18 months.
Lesions in the oral cavity with Candida spp. can be characterized by pseudomembranous plaques, erythema with erosions and ulcers, hyperplastic, yellowish-whitish plaques and crusting or fissuring of the lips. Other signs often reported are oesophagitis, gastritis and enteritis. Candidal vulvovaginitis in women is a common feature. Skin lesions include intertrigo, folliculitis and onychomycosis.
Disseminated candidiasis is a common consequence of HIV infection in individuals who are neutropenic.
CONTROL OF FUNGAL INFECTIONS
Fungal disease agents are widespread either in the environment or in farm and pet animals, the latter serving as asymptomatic carriers. This makes the chances of contact with these insidious infective agents very high. Usually the infections are benign and mild but the immunocompromised persons are unable to counteract the infections. This should always be taken into serious consideration and proper hygienic attitudes followed in order to minimize health risks.
As a result, the following general rules are of paramount importance:
wash hands after contact with soil or animal hairs;
avoid puncture wounds from thorns and slivers;
avoid inhaling soil or dust;
avoid exposure to chicken or pigeon coops, bird roosts and bat-inhabited caves.