Grossly unusual epidemiological features were noted that, to this day, have not been definitively explained. This study performed a historical reanalysis of the data to reveal an estimated geographic involvement of , km 2 , with , cattle and 17, human cases. Here we present the first documented geotemporal visualization of the human anthrax epidemic.
Anthrax is a potentially lethal disease caused by Bacillus anthracis , an aerobic spore-forming bacterium that exists in a complex ecological cycle predominantly involving herbivorous mammals and man. Persistence of anthrax in the environment is due to soil borne spores that remain viable for decades. Anthrax was first recognized in colonial times in southern Africa in and was placed on the list of scheduled diseases in South Africa in Europeans noted the persistent spread of anthrax in their cattle herds and eventually pushed for control programs that yielded the development of vaccines from onward.
In , South Africa had reported the death of 30,—60, cattle; however, once vaccination was initiated, a dramatic reduction in bovine anthrax was noted. In , during the context of the Rhodesian Counterinsurgency, an unprecedented anthrax epidemic in livestock and humans began in Rhodesia.
The epidemic progressed largely unchecked until the mids as the largest known anthrax epidemic in history. This event was documented by Davies in a three-part descriptive study from to that was limited to three of five involved provinces Davies, ; Davies, ; Davies, Additional primary source documentation was limited that provided greater insight into the location, case count, spread, and etiology of this epidemic.
A total of 10, human cases and approximately deaths 1. The majority of reported human cases were the cutaneous form of the disease; however, all known clinical forms of anthrax infection were documented during the course of the epidemic. The universally acknowledged source of human cases was cattle infected in rural, noncommercial farming areas known as Tribal Trust Lands Davies, ; Davies, ; Davies, The majority, if not all of the cases were among indigenous African farmers living on Tribal Trust Lands.
The two primary agricultural land classifications of Rhodesia in the late s were Tribal Trust Lands and commercial farming areas. Tribal Trust Lands covered Over four million people lived in the Tribal Trust Lands, , of them belonging to indigenous African farming families; this represented the majority of the rural indigenous population of the country at twice the population density of the Europeans living on the commercial agricultural areas.
The majority of cattle raised on the Tribal Trust Lands were used for agricultural labor, personal consumption, trade, and sources of fertilizer. Commercial agricultural areas included farms owned by European farmers who raised cattle for profit, as well as tobacco and other cash crops.
The land appropriated for these farms was roughly equal in size to the Tribal Trust Lands and was located in fertile areas World Bank, ; Whitlow, a ; Whitlow, b. African lineages of cattle were comprised of Mashona , Matabele , Zansi , Amabula , Kavuvu , Amabowe types and had been present in Rhodesia since at least the early s, which was the limit of documented history in this region of the world. Cattle were an integral part of migrant indigenous peoples of the region during this period.
These breeds intermingled with European stock introduced during the colonial period Mwatwara, Loosely considered, the African lineages resided on the Tribal Trust Lands, whereas the European lineages resided on commercial agricultural lands.
Prior to , Rhodesians had destroyed much of the indigenous wildlife during the expansion of cattle ranching. However, after , concerted effort was directed to the re-establishment of game and wildlife both on private ranches and in national parks. Prior to the war, the national anthrax control program was considered one of the most advanced and effective in Africa.
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This was a program that had been in place since approximately the mids. During the war, vaccination for anthrax was maintained largely on commercial as opposed to Tribal Trust Land farms due to chronic distrust of indigenous Africans directed towards European veterinary practice Mwatwara, Anthrax was rare in Rhodesia prior to , as shown in Fig. In , 41 cattle died of anthrax in Matabeleland Province, which was the first documented appearance of anthrax in Rhodesia.
In , 14 pigs and one donkey in Ardbennie and six cattle in Umganin, Bulawayo, died of anthrax. At Mount Hampden, nine cattle died in a limited outbreak in A larger epidemic in Shamva two years later resulted in the deaths of head of cattle on 18 farms.
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In , 18 cattle died in Hartley, Mtoko, and Shamva. All of these outbreaks were in western Rhodesia, north of Hartley MacAdam, There were six human cases and two deaths reported in the Mhondoro outbreak; the high fatality rate was attributed to delays in seeking timely medical attention Whitlow, b. Data on human cases were unavailable for the Chipinga and Mount Darwin outbreaks. No outbreaks of anthrax were documented in Rhodesian wildlife until Clegg et al.
The majority of reported human cases in these earlier outbreaks were cutaneous and, to a much lesser degree, gastrointestinal; infections were acquired from handling or eating infected livestock Davies, ; Davies, ; Davies, The approximate annual number of human cases reported nationally was 6 per year, for a total of cases and 20 fatalities from to Davies, The purpose of this study was to re-examine the — anthrax epidemic in Rhodesia in light of new data and analytic insights gained in the years since this important event.
We also reviewed all available veterinary and agricultural literature published in Rhodesia from to Historical land classification maps published for Rhodesia from to were obtained from the United States Library of Congress Surveyor-General, All available original manuscripts regarding anthrax in Rhodesia were reviewed, and a reanalysis of the epidemiological data contained therein was performed. We examined references to epidemic features such as historical pre-epidemic data, route of infection, severity of disease, meteorological data and seasonality, host animals, potential vectors, and vaccination coverage.
The sources of these different aspects of the epidemic are referenced in the results section. World Meteorological Organization archival average temperature and precipitation data for Rhodesia was used to assess meteorological anomalies for — World Bank, Anomalies were calculated using the following equation:. Where monthly data for — was used to calculate the monthly average and standard deviation. The month and year of first cases reported to these district hospitals was the only data available; continuous monthly times series case counts were not available.
Because nearly all of the human anthrax cases followed contact with cattle exhibiting signs of anthrax infection, we investigated the availability of bovine anthrax data from to We were unable to identify any surviving record of bovine anthrax data for this time period S. Chikerema, , personal communication. Geospatial cluster analysis was performed using the Kulldorff space-time permutation model resident in SaTScan v9. Default settings were used for the analysis to allow for identification of possible seasonal patterns.
First recognition of the epidemic was in Nkai District, Matabeleland Province, November , with a low number of human cases reported until June All of the cases were associated with the butchering and skinning of local cattle. Nkai Hospital would later report over cases from January to October , which was 1.
Approximately half of these cases required hospitalization, with 17 fatalities case fatality rate 3. The remainder died of sepsis that followed a cutaneous lesion. This was considered the first phase of the epidemic Davies, ; Davies, ; Davies, The epidemic smoldered until mid, when a second phase of the epidemic was apparent.
Case counts abruptly increased from September to November Fig. While extreme meteorological phenomena were not reported previous to or during the time period of the epidemic, higher than normal precipitation occurred in early Fig. Geotemporal variation in epidemic progression was observed at the provincial level Fig. Midlands Province was noted to begin peaking in October Fig. This was suggestive of a general southwest to northeast progression.
The patients were dominantly Tribal Trust Land inhabitants, with rare documentation of cases among those in the tanning industry Davies, ; Davies, Over the course of five months November —March , explosive spread of anthrax in Mashonaland Province had encompassed 13 districts and , km 2 Davies, ; Davies, ; Davies, A dramatic surge in human cases was observed ahead of the peak of the rainy season.
Arrows indicate the start of the first yellow and second red phases of the human epidemic, in November and September , respectively. Anomaly calculations used data from — see Materials and Methods. Arrows indicate the start of the first yellow and second red phases of the human epidemic, respectively.
These patients were referred to the hospital from across Mashonaland Province. All were Tribal Trust Land inhabitants except one individual from a tanning facility. Resource strain at the hospital was reflected in demand for hospitalizations, as noted in February and December , which was the result of two waves of patients who were hospitalized for two to five weeks.
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By March , the Beatrice Road Infectious Diseases Hospital reported that the most common reason for admission to their hospital was anthrax. The number of cases seen at Beatrice Road was considered enough to prompt concerns about contamination of the hospital with anthrax spores, which resulted in heavy use of masks, gowns and gloves until supplies were unable to meet the demand. However, no infection was noted among healthcare providers or between patients. Although many medical facilities reported abrupt, significant strain on their resources, fatality rates were considered very low and manageable.
There was no report of antimicrobial resistance; rather, the vast majority of the patients were effectively managed with penicillin.
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There was no indication of a penicillin shortage Davies, This hospital, by March , reported that anthrax was the leading reason for hospital admission. The facility experienced resource strain in two periods that coincided with two waves of patients in February and again in December Inhalation, gastrointestinal, and meningitis presentations were documented at the Beatrice Road Infectious Diseases Hospital as well as additional hospitals Davies, Five cases of anthrax meningitis, all fatal, out of 18 total cases seen were reported over the course of 12 months at Parirenyatwa General Hospital, also in Salisbury.
This facility had not previously seen a single case of anthrax from to mid All of these fatal cases had cutaneous lesions that followed contact with cattle upon presentation. Several of these cases had reported a painful insect bite that preceded development of the classic anthrax eschar lesion. Death was observed within one week of initial symptoms.
The unusual volume and variety of clinical presentations led to comparisons at the time to the Sverdlovsk, U. The Sverdlovsk outbreak was later shown to be an accident of a biological weapons laboratory Meselson et al.
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Figure 8 displays where human cases were first recognized, at the finest temporal and spatial resolution the epidemiological data allowed i. Time series data for case counts for district level hospitals was unavailable; therefore data regarding multiple epidemic waves seen for a given hospital was unavailable with the exception of the Beatrice Road Infectious Disease Hospital Fig. We attempted to further elucidate the hopping phenomenon by using a combination of centroid distance measurements and the Kuldorff statistic.
The Kuldorff space-time permutation highlighted four clusters of non-significant, but increased relative risk for high anthrax activity as shown in Table 1 and displayed in Fig. The map corresponding to November in Fig. Another example of a hop was in March , with spread to Chilimanze, Charter, and Seluweke. These hops involved distances of 40—50 km.
The mean of outbreak coordinates is indicated as a centroid coordinate, where each time step is associated with spatial movement of that coordinate. Only time steps associated with the first human cases for each site are shown. A—D Geotemporal clusters associated by the Kuldorff statistic with higher relative risk for high anthrax case counts are shown and denoted with a capital letter.
According to Davies, the spread of anthrax in humans involved a non-contiguous, heterogeneous distribution pattern. The clusters identified were associated with non-significant, higher relative risk Kulldorff, In the pre time period, systematic animal disease surveillance was not performed, especially on the Tribal Trust Lands. The epidemic among humans began nearly exclusively through contact with cattle across all areas of involvement in Rhodesia.
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