By: B Gianetti1, BM Katemba1, A Moraes1, C Groeneveld1, KM Kanyanga1, R Hamoonga1, ML Mazaba1
1. Information Systems Unit, Zambia National Public Health Institute.
Citation Style For This Article: B Gianetti, BM Katemba, A Moraes, et.al. Anthrax Update (2018-2019). Health Press Zambia Bull. 2019 3(2); pp 8-13.
Anthrax is a zoonotic disease caused by the spore-forming bacteria Bacillus anthracis. Anthrax spores are resistant to extreme environmental pressures and are able to persist in the soil. Humans generally acquire anthrax by ingesting infected meat or handling infected animal carcasses and products. People can develop three forms of anthrax infection dependent on the inoculation route: cutaneous, gastrointestinal, and pulmonary . Cutaneous anthrax occurs when spores enter the body through a wound or opening in the skin and has a 20% mortality rate if left untreated. Gastrointestinal anthrax infection occurs when persons ingest contaminated food and has a mortality rate between 25 to 60%. Pulmonary anthrax infection occurs when an individual inhales spores from the environment and has a mortality rate of greater than 80% .
Although several nations have made efforts to eliminate anthrax, infection still occurs in most sub-Saharan African countries. Anthrax is endemic in Zambia’s Luangwa valley and Zambezi floodplain [2–4]. Multiple anthrax outbreaks have been recorded in Zambia since 1990 due to the ingestion of contaminated beef and game meat, with case fatality rates (CFR) ranging from 4-20% [5–7].
In accordance with the Zambia Public Health Act (Chapter 295, Section 9), anthrax is a notifiable disease, and as such any suspected case requires a rapid Integrated Disease Surveillance and Response (IDSR) field investigation. Although reported anthrax cases have consistently decreased over the past 10 years, a recent outbreak of eight suspected cases in the Sesheke district of Western province prompted a review of reported anthrax cases in Western province from 2016-2019. This report presents an overview of the frequency and spatial distribution of suspected anthrax cases from January 2016 to January 2019.
We conducted a retrospective analysis of anthrax data collected using the IDSR system between January 2016 and January 2019 in order to identify trends in suspected anthrax cases in Zambia. Data was extracted from the weekly 2018 and 2019 IDSR reports as well as 2016 and 2017 outbreak investigation reports and analyzed using Microsoft Excel and Tableau.
The IDSR definition for a suspected cutaneous anthrax case is any person with an epidemiological link to confirmed or suspected animal cases or products who presents with a skin lesion that evolves over 1-6 days from a popular lesion to a vesicular lesion and ultimately to a black eschar accompanied by oedema. A suspected gastrointestinal anthrax case is any person with an epidemiological link to confirmed or suspected animal cases or products who presents with abdominal distress, characterised by nasusea, vomiting, anorexia, and fever. The suspected case definition for pulmonary anthrax is any person with an epidemiological link to confirmed or suspected animal cases or products who presents with symptoms resembling acute viral respiratory illness, followed by rapid onset of hypoxia, dyspnea, high temperature, and X-ray evidence of meditational widening.
The majority of suspected anthrax cases occurred between July and December (Table 1). One hundred and twenty-seven suspected
Table 1. Suspected Anthrax cases 2016- 2019
anthrax cases were reported across Muchinga and Western provinces in 2016. Ninety cases were reported in Western province in 2017, and only four suspected anthrax cases were reported in Western province in 2018. Samples for laboratory testing were collected from about 17% of reported suspected anthrax cases (Table 1).
An anthrax outbreak occurred in Muchinga district in September 2016 that consisted of 79 cases. The majority of suspected cases presented with cutaneous infection, were under 20 years of age, and reported having consumed hippopotamus meat (96%) . Of the twelve samples collected from suspected anthrax cases, three samples tested positive for B. anthracis (Table 1, ).
Except for the 2016 outbreak in Muchinga province, all reported outbreaks between 2016 and 2019 occurred in Western province (Table 1). Within Western province, four anthrax outbreaks were reported in 2016 and six in 2017. Between November 2016 and February 2017 anthrax outbreaks resulted in 87 cases and 6 deaths in Shangombo, Nalolo, Kalabo, and Limulanga districts. In July 2017 a small outbreak consisting of two suspected anthrax cases occurred in Kalabo district, and from September to November 2017 anthrax outbreaks resulted in 49 suspected cases and two deaths in Nalolo, Sioma, Senanga, and Shangombo districts (Table 1, Figure 1).
The 2016/2017 outbreaks in Western province comprised 138 suspected anthrax cases and 8 deaths (CFR 5.8%). Slightly more than 50% of all suspected cases were male, and almost half of all cases were between the ages of 5 and 19 years of age (44.9%) (Table 2). The majority of cases were reported in Kalabo and Shangombo districts (62.3%) (Table 2, Figure 1). One hundred and seventeen cases presented with cutaneous anthrax infection (84.8%), eleven cases had gastrointestinal anthrax (8.0%), and six cases presented with pulmonary anthrax (4.3%) (Table 2). Nearly all suspected anthrax cases received treatment (97.8%), most commonly at an outpatient health facility (88.4%). However, about three quarters (76.8%) of all suspected anthrax cases did not have a specimen collected for laboratory testing. Of the 28 specimens that were tested for B. anthracis, only 15 (53.6%) tested positive for anthrax infection (Table 2).
Figure 1. Map of suspected anthrax cases in Western province 2016 – 2019
Table 2. Characteristics of suspected anthrax cases in Western province 2016-2017
Table 3. Characteristics of anthrax deaths in Western province 2016-2017
Although the majority of cases reported during the 2016/2017 anthrax outbreaks in Western province were cutaneous infections, deaths due to anthrax occurred primarily amongst cases with gastrointestinal anthrax infections (62.5%) (Table 3). Deaths were reported in Kalabo, Nalolo, Shangombo, and Sioma districts. Three of eight (37.5%) reported anthrax fatalities did not receive treatment, and of those who sought care, 62.5% were treated at an inpatient health facility (Table 3).
Four isolated suspected cases of anthrax occurred in Limulunga, Shangombo, and Senanga districts in Western province in 2018. Furthermore, a recent outbreak in Sesheke district in Western province in January 2019 amassed eight suspected anthrax cases (Table 1, Figure 1). Laboratory samples were not tested from any suspected case in 2018 and 2019 (Table 1).
Between January 2016 and January of 2019 nine outbreaks and 265 suspected cases of anthrax were reported. During this period, one outbreak occurred in Chama district of Muchinga province and all other outbreaks occurred in Western province. In Western province, suspected anthrax cases were reported from Kalabo, Nalolo, Shangombo, Sioma, Senanga, Limulunga, and Sesheke districts. The highest numbers of suspected cases were reported in Shangombo and Kalabo districts, and the majority of anthrax cases occurred between the months of July and December. Over 80% of cases reported in Western province in 2016 and 2017 were cutaneous infections; however, 62.5% of anthrax fatalities were cases with gastrointestinal infections.
Traditionally, the majority of anthrax outbreaks in Zambia have occurred in Western province. A large outbreak occurred in Western province in 1990, during which 220 cases were documented. Between 1991 and 1998 a total of 248 cases and 19 deaths were reported across eight districts in Western and North-western provinces. Most cases consisted of gastrointestinal anthrax, although 33 cases presented with cutaneous anthrax infection . Between 1999 and 2007 a total of 1,790 anthrax cases and 83 anthrax deaths were reported in the Kalabo, Lukulu, Mongu, Kaoma, Senanga, and Sesheke districts in Western province, and a small outbreak consisting of 3 cases of cutaneous anthrax was investigated in five villages in Sesheke district in 2010 [4,8].
Most outbreaks in Western province are associated with suboptimal vaccination of cattle and transmission to humans due to contact with infected animals and consumption of found animal carcasses [5,6]. As such, farming families and persons classified as food insecure have a high risk of contracting anthrax . Historically, an increase of anthrax outbreaks in Zambia bas been observed between June and December, when the dry climate promotes increased human and livestock occupancy of the floodplain .
Alternatively, anthrax outbreaks in Muchinga province have been associated with the consumption of contaminated hippopotamus meat. The majority of anthrax cases reported during the 2016 Chama outbreak responded that they had eaten hippo meat. Moreover, an anthrax outbreak investigated in Chama district of Muchinga province in 2011 also found an association between anthrax infection and contact with and consumption of contaminated hippopotamus meat. Similar to the 2016 outbreak, a vast majority (95%) of cases presented with cutaneous anthrax .
Regardless of the location of an anthrax outbreak or the type of anthrax infection, less than 20% of suspected anthrax cases had specimens collected for laboratory diagnosis. Of the samples that were tested from cases during the 2016 and 2017 Western province anthrax outbreaks, 46.4% tested negative for a Bacillus anthracis infection. However, nearly all suspected cases received treatment for anthrax. Collection of samples from suspected animal and human infections is required to improve anthrax surveillance and help monitor the potential development of antimicrobial resistance in endemic Bacillus anthracis strains.
Conclusions and recommendations
Previous efforts to control anthrax outbreaks in endemic regions include mass vaccination of livestock, quarantine of infected animals, burning or burying of animal carcasses, and sensitization of the community . Despite these measures, the close proximity of people and animals and food insecurity in the region continue to drive anthrax transmission [8,11,12]. While most people are aware of the threat of anthrax, entrenched behaviors and cultural practices are difficult to change. Continued outbreaks in Western province highlight the importance of increasing community sensitization and health education campaigns in the area. Moving forward, a well-coordinated One Health approach is required to prevent animal and human anthrax infections in endemic regions of Zambia.
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