We see much discussion of global spread and potential pandemics from zoonotic infectious threats (e.g. Ebola, MERS, cryptosporidiosis) and vector-borne threats (e.g., Chikungunya, dengue). Some of these are both zoonotic and vector-borne (e.g., West Nile virus, Chagas', leishmaniasis, Rift-Valley fever). However, there seems to be less emphasis on the potential for geographical spread, or even global spread, of sapronotic infectious agents (e.g., melioidosis, legionellosis, flesh-eating bacteria) that are not vector-borne or specifically associated with other animals, but which tend to build up in certain environments and could be introduced into similar distant environments by internationally transported contaminants. A good discussion of potential sapronotic threats might raise awareness of potential threats and encourage more vigilance in surveillance and preparedness.
I think that cólera may be a sapronotic disease that may be spread from one couutry to another by contaminated food or water
I think the proactive nature of your coomments is a good start. It's always nice to have an idea that a certain situation may arise in a certain area; that way steps may be able to be taken to prevent them.
I think the spore-forming organisms from soil would most likely fit into this category. Although anthrax is primarily associated with herbivores, it has been imported into the U.S. on goat skin drums made in Africa. For that matter, we still have naturally occurring anthrax in buffalo and occasionally in cattle in the U.S. Anthrax spores are notoriously hardy and can remain in a viable state in soil for 100 yrs. or more. Another dangerous soil spore-former is Clostridium botulinum, perfringens and tetani. In addition their are molds and other saprophytes that are very toxic for humans that can build up under certain environmental conditions. You will find others if you "Google" agroterrorism.
Thanks for teaching me a new term. I had heard of saprophytic but not sapronotic agents. I suppose you could think of them as "incidental" pathogens. Things like Legionella can live quite well without a host. This is an interesting topic.
Well, legionellosis has certainly made the news from time to time, and MRSA has as well. I acquired an MRSA infection while working in Ethiopia which nearly cost me my leg and can attest that it's a very nasty infection indeed.
If I think of significant sapronotic diseases, those that spring to mind are fungi (e.g. histoplasmosis, aspergillosis, cryptococcosis, etc), some bacterial diseases (e.g., legionellosis, Clostridiosis, tetanus, etc), and some protozoa (amebic meningoencephalitis, etc).
But I think that the major reason that sapronotic infections have generally not received the same degree of press attention as zoonotic infections is simply their relatively limited epidemic potential. To take one example, invasive amebiasis can in some cases have a mortality which comes close to that of hemorrhagic fevers such as Ebola. It doesn't evoke the same degree of worry though, because the risk of human to human spread is very low. Unlike the recent multi-city outbreak of Ebola, for example, outbreaks of sapronotic infection can be controlled simply by locating the source and restricting access to it. Even where you have persistent infection among the local population, it tends not to spread.
In contrast, HIV, SARS, Ebola and now MERS have all relatively recently made the jump from animal hosts to humans and demonstrated the ability to become anthroponotic, while West Nile and Chikungunya virus have both spread rapidly over areas where they were previously unknown and are now infecting humans there. In both cases, the ability to establish themselves in human or animal hosts gives these diseases more "reach" than typical sapronotic diseases.
I say typical, because there are some grey zones: Anthrax, for example is a sapro-zoonoitic disease, that has both animal and environmental reservoirs. These have to be taken very seriously because they combine the features of an animal host (with potential for rapid spread) and an environmental reservoir (potential for persistence).
Thanks for your interesting and very thorough answer. I have a question on another topic that's very speculative. Has anyone noticed that the filoviruses look more like tobacco mosaic virus than any of the other animal viruses? Now, I'm not attempting to say that there's a relationship, but it struck me as being very strange. Rhabdoviruses look like bullets, but no other animal viruses yet described have that long, filamentous structure. Any thoughts about this, anyone?
Hi Odile!
Leishmaniasis is a zoonose rather than a sapronose, but you are right, it is spreading. Not just in Africa, either - we have had three substantial outbreaks in the EU in 2011-2013 (two in Spain, one in Italy: a mixture of cutaneous and visceral disease). This illustrates the problems with zoonoses: the disease has never really disappeared in Europe (especially Greece and the Balkans). It's endemic in dogs and hares in the Mediterranean periphery, which means not only is eradicating it almost impossible, but it can (and does) spread to the animal hosts in different areas, making it impossible to contain. Since the insect hosts can also range north of the Mediterranean areas, we see sporadic cases in central Europe, although it is not (yet) endemic. Given the warming climate though, it's almost certainly just a matter of time before it does become endemic north of the Alps.
Cryptosporidiosis has never spread within the US yet, but presumably has that potential if inoculated into other desert environments. It has an episodic, rather than epidemic, type of natural history and does not pose a huge threat to human life. However, we do not know what might happen to otherwise naive wildlife.
I agree with David that this might be an important issue. To sapronoses mentioned by him I would add some others caused by agents such as, e.g., Vibrio parahaemolyticus, V. vulnificus (and certain additiopnal vibrios), Clostridium spp., Mycobacterium spp. (M. kansasii, M. marinum, M. haemophilum, M. ulcerans etc.), Rhodococcus equi, Sporothrix schenckii, Fusarium spp., Cryptococcus spp. and other pathogenic fungi, Naegleria fowleri, Acanthamoeba spp. In most of them, their distribution and spreading potential are not well known.
Great points, Zdenek! Thanks for the input. I am especially interested in oppotunistic amoebae such as Naegleria, Acanthamoeba, and Balamuthia. These have caused infections, generally fatal, in the United States just within the last 2-3 years, and have resulted in many cases in many parts of the world. I'll add your suggestions to my growing list. It does seem that more of these should be incorporated into routine biomonitoring programs for potential environmental health threats.
I tried to summarize the list of sapronoses in the following publication, which has an attachment
Hubálek Z. (2003): Emerging human infectious diseases: anthroponoses, zoonoses, and sapronoses. Emerg. Infect. Dis. 9: 403-404.
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