zoonoses and communicable diseases common to ... - PAHO/WHO

ANTHRAX 25Figure 2. Anthrax. Transmission cycle.Cows andcalves, sheep,goats, horses,swine, dogsinfected withB. anthracisGround contaminatedwith open cadavers,secretions, andexcretionsIngestionSusceptible(not vaccinated)cows and calves,sheep, goats,horses, swine,dogsMainly by contact with dead animals,hides, wool; ingestion of anthracicmeat; inhalation of sporesManskin favors transmission. Products made from contaminated hair (e.g., shavingbrushes), skins (e.g., drums), and bone meal (e.g., fertilizer) may continue to besources of infection for many years. Transmission from animals to man is possibleby means of insects acting as mechanical vectors, but reliably documented cases arefew. A recent case occurred in a Croatian villager who was probably stung by ahorsefly and developed a case of cutaneous anthrax on the back of her neck. The presumedsource of infection was a cow close to her home that had died of anthrax(Braderic and Punda-Polic, 1992).Pulmonary anthrax comes from inhaling spores released from contaminated woolor animal hair.The source of infection for the gastrointestinal form is domestic and wild animalsthat died from anthrax. The pathway of transmission is through the digestive tract.Cases have been observed in Asia, Africa, and Latin America.Animals contract the infection mainly by ingestion of pasture or water contaminatedwith B. anthracis spores, especially in places near anthrax-infected carcasses.An animal dying of anthrax produces an enormous quantity of B. anthracis in its tissues,and if the carcass is opened, the bacilli sporulate, contaminating the soil, grass,and water. Animals that graze in the contaminated area become infected themselvesand produce new foci of infection. Animals and birds that feed on carrion can transportthe infection some distance. The most serious outbreaks occur during dry summersafter heavy rains. The rain washes spores loose and concentrates them in lowspots, forming so-called “cursed fields,” that are usually damp areas with glacialcalcareous soils containing abundant organic material and having a pH above 6 (VanNess, 1971). Nevertheless, outbreaks of anthrax may occur in acidic soil, as hap-