Anthrax epidemiology and demographics: Difference between revisions
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Human Incidence
The major sources of naturally acquired human anthrax infection are direct or indirect contact with infected animals, or occupational exposure to infected or contaminated animal products. The incidence of the natural disease in humans is dependent on the level of exposure to affected animals and, for any one country, national incidence data for non-industrial cases reflect the national livestock situation.
Historical analysis of epidemiological data globally reveals the following approximate ratios:
- In northern europe and countries with similar epidemiological situations there has been one human cutaneous case per 10 livestock carcasses butchered
- In Africa, India, and the southern Russian Federation, there can be some 10 human cutaneous and enteric cases per single carcass owing to rural malnutrition in the former and poor veterinary supervision in the latter. This has produced significant numbers of human cases each year in Chad, ethiopia, india, Zambia and Zimbabwe.
While enteric anthrax is frequently lethal, subclinical cases, which provide subsequent immunity, are believed to occur with some frequency also. These would contribute indirectly to persistence of the disease by engendering the concept among indigenous populations that the risk of contracting lethal disease from consuming meat from animals having succumbed to sudden death is not very high.
Some caution should be exercised in making projections of potential human cases based on fixed human: animal ratios. Economic conditions, surveillance data quality and dietary habits are examples of variables that may dramatically alter the situation from area to area. For example in the united States and north-western europe, cutaneous anthrax associated with animal anthrax has been rare since the first half of the 20th century, with most cutaneous cases being associated with processing of imported goat hair, hides and other animal products. despite
The rarity of the human disease since then, many thousands of animal cases have occurred. Similarly, in Haiti human cutaneous anthrax is quite common, but reports of animal anthrax are essentially non-existent despite a well-documented problem with B. anthracis-contaminated goatskin products. the value of hides and cultural demands for caretakers in at least some regions of Africa to preserve as much as possible from dead animals to present later to the owner exacerbate the problem of persisting contaminated animal parts.
Unlike cutaneous anthrax, ingestion anthrax is notably rare in Haiti, presumably because of the local practice of cooking all meat well before consumption. In other countries such as Thailand, ingestion anthrax is associated with consumption of undercooked meats and in sub-Saharan Africa, the value of the meat from an animal that has died unexpectedly outweighs the perceived risks of illness that might result from eating it (section 9.7). evidently intestinal anthrax was quite a common disease on the Korean peninsula prior to about 1940 and was still seen in the 1990s (oh et al., 1996).
Industrial anthrax incidence data can be inferred from the volume and weight of potentially affected materials handled or imported, taking into account the quality of prevention, such as vaccination of personnel and forced ventilation of the workplace. these relationships are essentially all that can be used for many countries where human anthrax is infrequently, erratically or incompletely reported. in addition, certain countries suppress anthrax report- ing at the local or national levels.
Human case rates for anthrax are highest in Africa and central and southern Asia. Where the disease is infrequent or rare in livestock, it is rarely seen in humans. however with low sporadic inci- dence comes forgetfulness of the risk and, when a case in livestock does occur, it may result in a surge in the number of cases and people exposed.
In contrast to reports of anthrax in animals, age- or sex-related bias is generally not apparent in human anthrax and differences in incidence have been readily explained in terms of likely exposure of the different groups to the organism. The lack of obvious age- or sex-related differences was also noted in the records of 112 anthrax cases occur- ring in 7 villages bordering the tarangire national Park in the united republic of tanzania between 1986 and 1999. There is, however, a bias towards higher occupational risk of exposure to anthrax in men in many countries.