This anthrax outbreak affected both humans and cattle. Cattle which were slaughtered or died due to unknown illnesses were the source of infection while meat was the vehicle of transmission. Most of the cases of human anthrax were cutaneous with the hands most affected. The case fatality rate was low. The following were found to be risk factor for contracting anthrax eating meat from cattle which were slaughtered or died alone due to unknown illnesses, source of meat from other villagers, skinning, cutting and cooking meat, cuts/ abrasions during skinning or cutting meat and belonging to religion which permits eating meat from cattle slaughtered or died alone due to unknown illnesses. Having heard of anthrax before was protective of contracting the disease. The carcasses of the dead cattle were incorrectly buried, and disinfection of sites were the animals died was not done. The district was not prepared to handle the outbreak. The outbreak was prolonged, and it took time for the district to institute control measures.
The anthrax eschar was more common in hands. This was consistent with the findings from other studies [15, 16]. This is because hands are used for handling meat and are at higher risk of developing abrasions, bruises and cuts which creates the route for entry of the anthrax spores. The case fatality rate for this outbreak was very low. The finding is consistent with other studies which have also recorded low fatality cases in anthrax outbreaks [17, 18]. The low case fatality rate in anthrax outbreaks might be due to the fact that the commonest form anthrax i.e. cutaneous anthrax has the least mortality rate as compared to other form of anthrax [1]. In our study all the interviewed cases had cutaneous anthrax and the victim who died in this outbreak might have developed respiratory anthrax based on the described symptoms and signs. Respiratory anthrax has a higher mortality as compared to cutaneous anthrax [19, 20].
The following were found to be risk factor for contracting anthrax eating meat from a dead animal, skinning, cutting and cooking meat, cuts/ abrasions during skinning or cutting meat and religion which permits eating meat of a dead animal. These finding are consistent with other studies done locally and might be due to similarity of practices [15, 21, 22]. The reason why having cuts or abrasions was associated with contracting anthrax is due to the fact that during the process of preparation of meat cuts and abrasions are likely to develop and these creates access routes for the spores to the sub-dermal tissue [1]. Belonging to a religion which permits eating meat from animals which died on their own was associated with contracting anthrax. These finding is however not consistent with other study done locally where one’s religion belief on consumption of meat from a dead animal was a was not associated with contracting anthrax [15, 21]. Having heard of anthrax before was protective against contracting anthrax in our study. This is because those who heard of anthrax will be aware of the modes of transmission, signs and symptoms and preventive measures so they will not put themselves at risk [23].
The environment assessment showed some factors which increased the risk of anthrax in the area. There were inadequate grazing land and pastures in the affected areas. This outbreak started a few months before the rainy season, a period typically associated with lack of grazing grass. During this period the grass will be short which predisposes grazing cattle to ingestion of the anthrax bacilli due to overgrazing [24, 25]. Anthrax spores can survive for a long period of time in conducive soil conditions [26]. The presence of an army base in one of the affected wards raises the possibility of anthrax having been introduced to the area as part of bioterrorism during the liberation struggle [27]. One of the wards also bordered a game reserve. The sharing of grazing land with game often result in transmission of anthrax to livestock [28].
The outbreak was prolonged, and it took time for the district to institute control measures. The district delayed starting outbreak control measures. This might have been caused by several reasons. The district did not have an Emergency preparedness response plan and had no adequate resources to use which included protective clothing. Chloride of lime which is used for disinfection of sites where cattle died is corrosive. The zoonotic committees which are key in quick identification of zoonotic diseases were not functional both at district and local level. As soon as the district started to institute outbreak control measures the outbreak did not prolong further. The massive health education and awareness campaigns conducted could have significantly contributed to the end of the outbreak [17, 21].
Strength of the study
Our study had most of the components of outbreak investigation practically implemented
A team was set up and prepared for the outbreak field work. A case definition was established which was used to identify, count and line list cases. We described the outbreak in terms of person, place and time together with risk factor analysis. Outbreak control and preventive measures were instituted, results disseminated and later the outbreak was controlled.
Limitations
However, our investigations had limitations. There was no laboratory diagnosis of anthrax in humans but laboratory confirmation in animals was performed. Of the 64 cases recorded in both Ward 22 and 23, we only managed to interview 39. We could not interview other cases due to distant. The small sample size affected the precision of our point estimates. Recall bias could have affected our results since data was collected after exposure and cases are usually more likely to remember the exposures more than controls.