Anthrax epidemiology and demographics
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Incidence of the natural disease in humans is dependent on the level of exposure to affected animals. For any country, national incidence data for non-industrial cases reflect the livestock situation. Human case rates for anthrax are highest in Africa and Central and Southern Asia. While, statistically, in Northern Europe and countries with similar epidemiological situations, there is one human cutaneous case per every 10 livestock carcasses butchered, there can be some 10 human cutaneous and enteric cases per single carcass butchered in Africa, India, and the Southern Russian Federation.[1]
Epidemiology and Demographics
Incidence
Non Industrial Anthrax
- Human case rates for anthrax are highest in Africa, Central and Southern Asia. In locations where the disease manifests infrequently in livestock, it is rarely seen in humans. However, low sporadic incidence may result in obliviousness and disregard, leading to a surge in the number of human exposures from a case in livestock.
- Historical analysis of global epidemiological data reveals the following approximate ratios:
- In Northern Europe and countries with similar epidemiological situations, there is 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. Rural malnutrition and poor veterinary supervision has resulted in 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, also occur. Because they lead individuals to perceive that there is a lower risk of contracting lethal disease, from the consumption of meat from animals having succumbed to sudden death, subclinical cases contribute indirectly to the diseases' persistence in indigenous populations.
- In regions where ingestion anthrax occurs commonly, oropharyngeal anthrax appears to be a relatively infrequent manifestation.
- Some caution should be exercised in making projections of potential human cases, based on fixed human to animal ratios. There are variables that may dramatically alter the situation from area to area, such as economic conditions, surveillance data quality, and dietary habits.
- 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 goat skin products. Unlike cutaneous anthrax, ingestion anthrax is notably rare in Haiti, presumably because of the local practice of cooking all meat well before consumption.
- 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.
- In other countries such as Thailand, ingestion anthrax is associated with consumption of undercooked meats.
- Intestinal anthrax was quite a common disease on the Korean peninsula prior to about 1940 and was still seen in the 1990s.
- 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.[1]
Industrial Anthrax
- 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.[1]
- In addition, certain countries suppress anthrax reporting at the local or national levels.[1]
Age
- In contrast to reports of anthrax in animals, age-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-related differences was also noted in the records of 112 anthrax cases, occurring in 7 villages bordering the Tarangire national Park in the United Republic of Tanzania between 1986 and 1999.[1]
Gender
- In contrast to reports of anthrax in animals, sex-related bias is generally not apparent in human anthrax. Differences in incidence have been readily explained in terms of likely exposure of the different groups to the organism.
- The lack of obvious sex-related differences was also noted in the records of 112 anthrax cases, occurring 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.[1]
Developed Countries
Developed countries, such as the United States and North-Western Europe, have lower incidence of anthrax.[1]
Developing Countries
Developing countries, such as Africa, India, Haiti, and the Southern Russian Federation have higher incidence of anthrax, particularly due to malnutrition and poor veterinary supervision.[1] However, unreliable reporting makes it difficult to estimate the true incidence of human anthrax in these countries.[2]