HISTOPLASMOSES is a dimorphic pathogen, a disease caused by a fungus found in BAT AND BIRD DROPPINGS.
It is also known as Darling's disease, reticuloendotheliosis, reticuloendothelial cytomycosis, Ohio Valley disease, tingo, and Maria fever. It is actually a very common disease in the Ohio and lower Mississippi River Valleys, but rarely causes severe disease.
Histoplasma capsulatum is called a thermal dimorph because it has two forms. In nature at "room temperature" about 25° C it takes on a mycelial (filamentous) form, forming the macroconidia. As well as smaller microconidia. At body temperature (37° C) it morphs into a yeast.
When inhaled into the alveolar spaces it is primarily the microconidia that germinate and then transform into small budding yeasts 2-5 um diameter. Yeast cells are found in reticuloendothelial system. The fungus also grows as a yeast in culture at 37° C.
Histoplasma capsulatum yeast and mycelial cultures at different temperatures. The true human-pathogenic fungi have a yeast phase inside the human body to get around the human immune system-- although the conidia formed by the mycelial form are the cause of infection. Not only does the phase shift, but there is a concomitant change in the chemicals making up the wall of the fungus. Thus the antigens change and the immune system must retool, giving the fungus just enough time to establish itself in the lungs. The other true human pathogens include:
- Blastomyces dermatitidis, cause of a lung disease called blastomycosis, Chicago disease, Namekagon River fever. This disease is endemic to the Central, Southern and Northern United States and Canada, as well as many other areas.
- Paracoccidioides brasiliensis, cause of the lung disease
- The other true human-pathogenic fungus is Coccidioides immitis, cause of coccidioidomycosis, also known as Valley fever. It is restricted mostly to the desert South west USA and the San Joachin Valley in California. It is probably the most virulent of the human pathogenic fungi. It is dimorphic, producing a mycelial form in nature and a spherule form in the host organism.
- In addition there are two other opportunistic pathogens that are dimorphic. Sporothrix schenckii causes "rose picker's disease," and must be traumatically implanted under the skin to cause infection. The other is Penicillium marneffei, which is an opportunistic fungal pathogen so far found only in South-east Asia.
- Histoplasma capsulatum calcification in spleenHistoplasma capsulatum yeast budding in tissueInfection results after inhalation of the conidia. This results in a variety of clinical manifestations. Approximately 95% of cases are inapparent, subclinical, or completely benign. The disease is diagnosed only by the X-ray findings of residual areas of pulmonary calcification and a positive histoplasmin skin test. Approximately 40 million people in the USA (that number is not a typo) have had the disease, and 200,000 new infections occur every year
- The remaining 5% develop a chronic progressive lung disease, a chronic cutaneous or systemic disease, or an acute fulminating rapidly fatal systemic infection. The latter form is particularly common in children. Following infection there is an acute alveolitis, and macrophages engulf the organism, resulting in an inflammatory reaction. Macrophages probably carry the organism to other parts of the body very early in the course of the infection.
Histoplasma capsulatum sign in a starling area. The fungus also forms a sexual state, forming spores by meiosis. It is a heterothallic ascomycete. The teleomorph or sexual state is Ajellomyces capsulatus found in the Arthrodermataceae, Onygenales, Ascomycota. It forms a gymnothecium, which is similar to the cleistothecium formed by powdery mildews, but the structure of a gymnothecium is much more open, allowing the spores to fall out and be dispersed.
The fungus has been found all over the world. Its growth is particularly associated with the guano and debris of birds and bats, particularly with birds that congregate in large numbers, such as starlings.
Before histoplasmosis came to be widely recognized (before the early 1950's), its disease symptoms were mistaken for tuberculosis . Of course that meant sufferers of the disease were given antibacterial antibiotics to treat the disease. This usually worsened the disease because after the bacteria were killed off there was essentially no competition for the fungus in the body and it could take over. A proper diagnosis is very important. So how much medical mycology study do you think the average doctor gets in medical school? Sometimes only one or two lectures!!! That certainly is not enough, especially with fungal diseases becoming so important because of people's compromised immune systems.
Histoplasmosis is a fungal infection caused by the Histoplasma capsulatum fungus.
It occurs throughout the world. In South Africa it is found everywhere except in Kwa-Zulu Natal.
The infection enters the body through the lungs. Histoplasma fungus grows as a mold in the soil, and infection results from breathing in airborne particles. Soil contaminated with bird or bat droppings may have a higher concentration of histoplasma.
There may be a short period of active infection, or it can become chronic and spread throughout the body. Histoplasmosis may have no symptoms. Most people who do develop symptoms will have a flu-like syndrome and lung (pulmonary) complaints related to pneumonia or other lung involvement. Those with chronic lung disease (such as emphysema and bronchiectasis) are at higher risk of a more severe infection.
About 10% of people with histoplasmosis will develop inflammation (irritation and swelling) in response to the initial infection. This can affect the skin, bones or joints, or the lining of the heart (pericardium). These symptoms are not due to fungal infection of those body parts, but to the inflammation.
In a small number of patients, histoplasmosis may become widespread (disseminated), and involve the blood, meninges (outer covering of the brain), adrenal glands, and other organs. Very young or very old people, or those who have a weakened immune system (due to AIDS, cancer, or transplant, for example) are at higher risk for disseminated histoplasmosis
However, please do not write to me about any of your medical problems caused by fungi. I am not a medical doctor.
Through inhalation of spores (conidia) from soil that may be contaminated with bat guano or bird droppings; not transmitted directly from person to person.
Distributed worldwide, except in Antarctica, but most often associated with river valleys. Activities such as spelunking, mining, construction, excavation, demolition, roofing, chimney cleaning, farming, gardening, and installing heating and air-conditioning systems are associated with histoplasmosis. Activities that expose people to areas where bats live and birds roost also increase risk. Outbreaks have been reported associated with travel to many countries in Central and South America, most often associated with visiting caves.
Incubation period is typically 3–17 days for acute disease. Ninety percent of infections are asymptomatic or result in a mild influenzalike illness. Some infections may cause acute pulmonary histoplasmosis, manifested by high fever, headache, nonproductive cough, chills, weakness, pleuritic chest pain, and fatigue. Most people spontaneously recover 2–3 weeks after onset of symptoms, although fatigue may persist longer. Dissemination, especially to the gastrointestinal tract and central nervous system, can occur in people who are immunocompromised.
Culture of H. capsulatum from bone marrow, blood, sputum, and tissue specimens is the definitive method. Demonstration of the typical intracellular yeast forms by microscopic examination strongly supports the diagnosis of histoplasmosis when clinical, epidemiologic, and other laboratory studies are compatible. EIA on urine, serum, plasma, bronchoalveolar lavage, or cerebrospinal fluid is a rapid diagnostic test commercially available
No bat has ever tested positive for canine rabies in South Africa.
Lyssaviruses are so-called rabies-related viruses. In South Africa two lyssaviruses have been associated with bats
Lagos Bat Virus is found at very low levels (less than one case a year) in the population of Wahlberg’s epaulletted fruit bats, and there have two cases of the disease in cats.
To date there has been no evidence of Lagos Bat Virus infecting people. Any fruit bat that dies for no obvious reason should be handed to a vet with a request that the bat be tested for Lagos. If the bat should test positive then it is recommended that a course of post exposure rabies shots be administered to anyone who had contact with the bat.
Duvenhage Virus is closely related to Lagos virus and has caused the death of two people in the North West Province of South Africa (1970 and 2006). In both cases the patients had been either bitten or scratched by an insectivorous bat some time before the disease manifested itself.
Always be careful not to get bitten when handling any wild animal, including bats. Use thick gloves or a cloth to handle bats and do not allow children to stroke or handle any grounded bat.
Anyone that is bitten by any wild or stray animal should immediately scrub the wound with soap and water and go within 24 hours to their nearest clinic to start a course of post-exposure rabies vaccinations. These vaccinations are free at State clinics.