Plague, caused by Yersinia pestis, is a widespread threat to endangered black-footed ferrets (Mustela nigripes) and their primary prey, prairie dogs (Cynomys spp.). Wildlife biologists most commonly manage plague using insecticides to control fleas, the primary vectors of Y. pestis. We tested edible baits containing the insecticides lufenuron and/or nitenpyram in prairie dogs. During a laboratory study, we treated 26 white-tailed prairie dogs (Cynomys leucurus) with lufenuron at 300 mg/kg body mass. All animals remained clinically healthy over the 9 wk monitoring period. Although serum lufenuron concentrations were >130 ppb in two treatment groups at week 1, concentrations declined to ≤60 ppb after 3 wk in non-torpid prairie dogs and after 7 wk in torpid prairie dogs. In a field experiment, we tested baits containing a combination of 75 mg lufenuron and 6 mg nitenpyram, respectively, in black-tailed prairie dogs (Cynomys ludovicianus). We uniformly distributed baits at 125 baits/ha on two plots (treated once) and 250 baits/ha on two plots (each treated twice 4.4 wk apart). Following treatments, flea abundance increased on prairie dogs and remained stable in burrows. Our findings indicate that baits containing lufenuron and nitenpyram, at the reported treatment rates, are ineffective tools for flea control on prairie dogs. Future experiments might evaluate efficacy of higher doses of lufenuron and nitenpyram, and repetitive treatments at differing intervals over time to evaluate potentially therapeutic treatments.

Plague, a fleaborne rodent-associated zoonosis, is a neglected disease with most recent cases reported from east and central Africa and Madagascar. Because of its low incidence and sporadic occurrence, most of our knowledge of plague ecology, prevention, and control derives from investigations conducted in response to human cases. Long-term studies (which are uncommon) are required to generate data to support plague surveillance, prevention, and control recommendations. Here we describe a 15-year, multidisciplinary commitment to plague in the West Nile region of Uganda that led to significant advances in our understanding of where and when persons are at risk for plague infection and how to reduce morbidity and mortality. These findings provide data-driven support for several existing recommendations on plague surveillance and prevention and may be generalizable to other plague foci.

Global health security depends on effective surveillance for infectious diseases. In Uganda, resources are inadequate to support collection and reporting of data necessary for an effective and responsive surveillance system. We used a cross-cutting approach to improve surveillance and laboratory capacity in Uganda by leveraging an existing pediatric inpatient malaria sentinel surveillance system to collect data on expanded causes of illness, facilitate development of real-time surveillance, and provide data on antimicrobial resistance. Capacity for blood culture collection was established, along with options for serologic testing for select zoonotic conditions, including arboviral infection, brucellosis, and leptospirosis. Detailed demographic, clinical, and laboratory data for all admissions were captured through a web-based system accessible at participating hospitals, laboratories, and the Uganda Public Health Emergency Operations Center. Between July 2016 and December 2017, the expanded system was activated in pediatric wards of 6 regional government hospitals. During that time, patient data were collected from 30,500 pediatric admissions, half of whom were febrile but lacked evidence of malaria. More than 5,000 blood cultures were performed; 4% yielded bacterial pathogens, and another 4% yielded likely contaminants. Several WHO antimicrobial resistance priority pathogens were identified, some with multidrug-resistant phenotypes, including Acinetobacter spp., Citrobacter spp., Escherichia coli, Staphylococcus aureus, and typhoidal and nontyphoidal Salmonella spp. Leptospirosis and arboviral infections (alphaviruses and flaviviruses) were documented. The lessons learned and early results from the development of this multisectoral surveillance system provide the knowledge, infrastructure, and workforce capacity to serve as a foundation to enhance the capacity to detect, report, and rapidly respond to wide-ranging public health concerns in Uganda.

BACKGROUND: The distribution of human plague risk is strongly associated with rainfall in the tropical plague foci of East Africa, but little is known about how the plague bacterium is maintained during periods between outbreaks or whether environmental drivers trigger these outbreaks. We collected small mammals and fleas over a two year period in the West Nile region of Uganda to examine how the ecological community varies seasonally in a region with areas of both high and low risk of human plague cases. METHODS: Seasonal changes in the small mammal and flea communities were examined along an elevation gradient to determine whether small mammal and flea populations exhibit differences in their response to seasonal fluctuations in precipitation, temperature, and crop harvests in areas within (above 1300 m) and outside (below 1300 m) of a model-defined plague focus. RESULTS: The abundance of two potential enzootic host species (Arvicanthis niloticus and Crocidura spp.) increased during the plague season within the plague focus, but did not show the same increase at lower elevations outside this focus. In contrast, the abundance of the domestic rat population (Rattus rattus) did not show significant seasonal fluctuations regardless of locality. Arvicanthis niloticus abundance was negatively associated with monthly precipitation at a six month lag and positively associated with current monthly temperatures, and Crocidura spp. abundance was positively associated with precipitation at a three month lag and negatively associated with current monthly temperatures. The abundance of A. niloticus and Crocidura spp. were both positively correlated with the harvest of millet and maize. CONCLUSIONS: The association between the abundance of several small mammal species and rainfall is consistent with previous models of the timing of human plague cases in relation to precipitation in the West Nile region. The seasonal increase in the abundance of key potential host species within the plague focus, but not outside of this area, suggests that changes in small mammal abundance may create favorable conditions for epizootic transmission of Y. pestis which ultimately may increase risk of human cases in this region.

The presence of bartonellae in invasive rats (Rattus rattus) and indigenous rodents (Arvicanthis niloticus and Cricetomys gambianus) from two districts in Uganda, Arua and Zombo, was examined by PCR detection and culture. Blood from a total of 228 R. rattus, 31 A. niloticus, and 5 C. gambianus was screened using genus-specific primers targeting the 16S-23S intergenic spacer region. Furthermore, rodent blood was plated on brain heart infusion blood agar, and isolates were verified as Bartonella species using citrate synthase gene- (gltA) specific primers. One hundred and four fleas recovered from R. rattus were also tested for the presence of Bartonella species using the same gltA primer set. An overall prevalence of 1.3% (three of 228) was obtained in R. rattus, whereas 61.3% of 31 A. niloticus and 60% of five C. gambianus were positive for the presence of Bartonella species. Genotypes related to Bartonella elizabethae, a known zoonotic pathogen, were detected in three R. rattus and one C. gambianus. Bartonella strains, similar to bacteria detected in indigenous rodents from other African countries, were isolated from the blood of A. niloticus. Bartonellae, similar to bacteria initially cultured from Ornithodorus sonrai (soft tick) from Senegal, were found in two C. gambianus. Interestingly, bartonellae detected in fleas from invasive rats were similar to bacteria identified in indigenous rodents and not their rat hosts, with an overall prevalence of 6.7%. These results suggest that if fleas are competent vectors of these bartonellae, humans residing in these two districts of Uganda are potentially at greater risk for exposure to Bartonella species from native rodents than from invasive rats. The low prevalence of bartonellae in R. rattus was quite surprising, in contrast, to the detection of these organisms in a large percentage of Rattus species from other geographical areas. A possible reason for this disparity is discussed.

Increasingly, the need to strengthen global capacity to prevent, detect, and respond to public health threats around the globe is being recognized. CDC, in partnership with the World Health Organization (WHO), has committed to building capacity by assisting member states with strengthening their national capacity for integrated disease surveillance and response as required by International Health Regulations (IHR). CDC and other U.S. agencies have reinforced their pledge through creation of global health security (GHS) demonstration projects. One such project was conducted during March-September 2013, when the Uganda Ministry of Health (MoH) and CDC implemented upgrades in three areas: 1) strengthening the public health laboratory system by increasing the capacity of diagnostic and specimen referral networks, 2) enhancing the existing communications and information systems for outbreak response, and 3) developing a public health emergency operations center (EOC) (Figure 1). The GHS demonstration project outcomes included development of an outbreak response module that allowed reporting of suspected cases of illness caused by priority pathogens via short messaging service (SMS; i.e., text messaging) to the Uganda District Health Information System (DHIS-2) and expansion of the biologic specimen transport and laboratory reporting system supported by the President's Emergency Plan for AIDS Relief (PEPFAR). Other enhancements included strengthening laboratory management, establishing and equipping the EOC, and evaluating these enhancements during an outbreak exercise. In 6 months, the project demonstrated that targeted enhancements resulted in substantial improvements to the ability of Uganda's public health system to detect and respond to health threats.

Rodents pose serious threats to human health and economics, particularly in developing countries where the animals play a dual role as pests: they are reservoirs of human pathogens, and they inflict damage levels to stored products sufficient to cause food shortages. To assess the magnitude of the damage caused by rodents to crops, their level of contact with humans, and to better understand current food storage and rodent control practices, we conducted a survey of 37 households from 17 subsistence farming villages within the West Nile region of Uganda. Our survey revealed that rodents cause both pre- and post-harvest damage to crops. Evidence of rodent access to stored foods was reported in conjunction with each of the reported storage practices. Approximately half of the respondents reported that at least one family member had been bitten by a rat within the previous three months. Approximately two-thirds of respondents practiced some form of rodent control in their homes. The abundance of rodents was similar within homes that practiced or did not practice rodent control. Together, our results show that current efforts are inadequate for effectively reducing rodent abundance in homes.

The cat flea, Ctenocephalides felis, is an inefficient vector of the plague bacterium (Yersinia pestis) and is the predominant off-host flea species in human habitations in the West Nile region, an established plague focus in northwest Uganda. To determine if C. felis might serve as a Y. pestis bridging vector in the West Nile region, we collected on- and off-host fleas from human habitations and used a real-time polymerase chain reaction-based assay to estimate the proportion of off-host C. felis that had fed on humans and the proportion that had fed on potentially infectious rodents or shrews. Our findings indicate that cat fleas in human habitations in the West Nile region feed primarily on domesticated species. We conclude that C. felis is unlikely to serve as a Y. pestis bridging vector in this region.

Over the past two decades, the majority of human plague cases have been reported from areas in Africa, including Uganda. In an effort to develop affordable plague control methods within an integrated vector control framework, we evaluated the efficacy of indoor residual spraying (IRS) techniques commonly used for mosquito control for controlling fleas on hut-dwelling commensal rodents in a plague-endemic region of Uganda. We evaluated both the standard IRS spraying (walls and ceiling) and a modified IRS technique that included insecticide application on not only on walls and ceiling but also a portion of the floor of each treated hut. Our study demonstrated that both the standard and modified IRS applications were effective at significantly reducing the flea burden and flea infestation of commensal rodents for up to 100 d after application, suggesting that IRS could potentially provide simultaneous control of mosquito and fleaborne diseases.

Plague is a flea-borne rodent-associated zoonotic disease that is caused by Yersinia pestis and characterized by long quiescent periods punctuated by rapidly spreading epidemics and epizootics. How plague bacteria persist during inter-epizootic periods is poorly understood, yet is important for predicting when and where epizootics are likely to occur and for designing interventions aimed at local elimination of the pathogen. Existing hypotheses of how Y. pestis is maintained within plague foci typically center on host abundance or diversity, but little attention has been paid to the importance of flea diversity in enzootic maintenance. Our study compares host and flea abundance and diversity along an elevation gradient that spans from low elevation sites outside of a plague focus in the West Nile region of Uganda ( approximately 725-1160 m) to higher elevation sites within the focus ( approximately 1380-1630 m). Based on a year of sampling, we showed that host abundance and diversity, as well as total flea abundance on hosts was similar between sites inside compared with outside the plague focus. By contrast, flea diversity was significantly higher inside the focus than outside. Our study highlights the importance of considering flea diversity in models of Y. pestis persistence.

Quantifying the abundance of host-seeking fleas is critical for assessing risk of human exposure to flea-borne disease agents, including Yersinia pestis, the etiological agent of plague. Yet, reliable measures of the efficacy of existing host-seeking flea collection methods are lacking. In this study, we compare the efficacy of passive and active methods for the collection of host-seeking fleas in both the laboratory and human habitations in a plague-endemic region of northwest Uganda. In the laboratory, lighted "Kilonzo" flea traps modified with either blinking lights, the creation of shadows or the generation of carbon dioxide were less efficient at collecting Xenopsylla cheopis Rothchild and Ctenocephalides felis Bouché fleas than an active collection method using white cotton socks or cotton flannel. Passive collection using Kilonzo light traps in the laboratory collected significantly more X. cheopis than C. felis and active collection, using white socks and flannel, collected significantly more C. felis than X. cheopis. In field studies conducted in Uganda, Kilonzo traps using a flashlight were similar in their collection efficacy to Kilonzo traps using kerosene lamps. However, in contrast to laboratory studies, Kilonzo flea traps using flashlights collected a greater number of fleas than swabbing. Within human habitations in Uganda, Kilonzo traps were especially useful for collecting C. felis, the dominant species found in human habitations in this area.

Plague, caused by the bacteria Yersinia pestis, is a severe, often fatal disease. This study focuses on the plague-endemic West Nile region of Uganda, where limited information is available regarding environmental and behavioral risk factors associated with plague infection. We conducted observational surveys of 10 randomly selected huts within historically classified case and control villages (four each) two times during the dry season of 2006 (N = 78 case huts and N = 80 control huts), which immediately preceded a large plague outbreak. By coupling a previously published landscape-level statistical model of plague risk with this observational survey, we were able to identify potential residence-based risk factors for plague associated with huts within historic case or control villages (e.g., distance to neighboring homestead and presence of pigs near the home) and huts within areas previously predicted as elevated risk or low risk (e.g., corn and other annual crops grown near the home, water storage in the home, and processed commercial foods stored in the home). The identified variables are consistent with current ecologic theories on plague transmission dynamics. This preliminary study serves as a foundation for future case control studies in the area.

In recent decades, the majority of human plague cases (caused by Yersinia pestis) have been reported from Africa. In an effort to reduce the risk of the disease in this area, we evaluated the efficacy of a host-targeted rodent bait containing the insecticide imidacloprid for controlling fleas on house-dwelling commensal rodents in a plague-endemic region of northwestern Uganda. Results demonstrated that the use of a palatable, rodent-targeted, wax-based bait cube was effective at reducing the prevalence of fleas on commensal rodents and flea burdens on these animals at day 7 postbait exposure, but lacked significant residual activity, allowing flea populations to rebound in the absence of additional bait applications. Our results indicate the use of a palatable host-targeted bait block containing imidacloprid was an effective technique for quickly reducing flea numbers on rodents in northwest Uganda and, thus, could be useful for lowering the potential risk of human flea bite exposures during plague outbreaks if applied continuously during the period of risk.

Plague, a life-threatening flea-borne zoonosis caused by Yersinia pestis, has most commonly been reported from eastern Africa and Madagascar in recent decades. In these regions and elsewhere, prevention and control efforts are typically targeted at fine spatial scales, yet risk maps for the disease are often presented at coarse spatial resolutions that are of limited value in allocating scarce prevention and control resources. In our study, we sought to identify sub-village level remotely sensed correlates of elevated risk of human exposure to plague bacteria and to project the model across the plague-endemic West Nile region of Uganda and into neighboring regions of the Democratic Republic of Congo. Our model yielded an overall accuracy of 81%, with sensitivities and specificities of 89% and 71%, respectively. Risk was higher above 1,300 meters than below, and the remotely sensed covariates that were included in the model implied that localities that are wetter, with less vegetative growth and more bare soil during the dry month of January (when agricultural plots are typically fallow) pose an increased risk of plague case occurrence. Our results suggest that environmental and landscape features play a large part in classifying an area as ecologically conducive to plague activity. However, it is clear that future studies aimed at identifying behavioral and fine-scale ecological risk factors in the West Nile region are required to fully assess the risk of human exposure to Y. pestis.