Intervention To Stop Transmission of Imported Pneumonic Plague - Uganda, 2019.

Plague, an acute zoonosis caused by Yersinia pestis, is endemic in the West Nile region of northwestern Uganda and neighboring northeastern Democratic Republic of the Congo (DRC) (1-4). The illness manifests in multiple clinical forms, including bubonic and pneumonic plague. Pneumonic plague is rare, rapidly fatal, and transmissible from person to person via respiratory droplets. On March 4, 2019, a patient with suspected pneumonic plague was hospitalized in West Nile, Uganda, 4 days after caring for her sister, who had come to Uganda from DRC and died shortly thereafter, and 2 days after area officials received a message from a clinic in DRC warning of possible plague. The West Nile-based Uganda Virus Research Institute (UVRI) plague program, together with local health officials, commenced a multipronged response to suspected person-to-person transmission of pneumonic plague, including contact tracing, prophylaxis, and education. Plague was laboratory-confirmed, and no additional transmission occurred in Uganda. This event transpired in the context of heightened awareness of cross-border disease spread caused by ongoing Ebola virus disease transmission in DRC, approximately 400 km to the south. Building expertise in areas of plague endemicity can provide the rapid detection and effective response needed to mitigate epidemic spread and minimize mortality. Cross-border agreements can improve ability to respond effectively.

Use of Insecticide Delivery Tubes for Controlling Rodent-Associated Fleas in a Plague Endemic Region of West Nile, Uganda.

Plague is a primarily flea-borne rodent-associated zoonosis that is often fatal in humans. Our study focused on the plague-endemic West Nile region of Uganda where affordable means for the prevention of human plague are currently lacking. Traditional hut construction and food storage practices hinder rodent exclusion efforts, and emphasize the need for an inexpensive but effective host-targeted approach for controlling fleas within the domestic environment. Here we demonstrate the ability of an insecticide delivery tube that is made from inexpensive locally available materials to reduce fleas on domestic rodents. Unbaited tubes were treated with either an insecticide alone (fipronil) or in conjunction with an insect growth regulator [(S)-methoprene], and placed along natural rodent runways within participant huts. Performance was similar for both treatments throughout the course of the study, and showed significant reductions in the proportion of infested rodents relative to controls for at least 100 d posttreatment.

Engagement with Traditional Healers for Early Detection of Plague in Uganda.

In rural Uganda, many people who are ill consult traditional healers prior to visiting the formal healthcare system. Traditional healers provide supportive care for common illnesses, but their care may delay diagnosis and management of illnesses that can increase morbidity and mortality, hinder early detection of epidemic-prone diseases, and increase occupational risk to traditional healers. We conducted open-ended, semi-structured interviews with a convenience sample of 11 traditional healers in the plague-endemic West Nile region of northwestern Uganda to assess their knowledge, practices, and attitudes regarding plague and the local healthcare system. Most were generally knowledgeable about plague transmission and its clinical presentation and expressed willingness to refer patients to the formal healthcare system. We initiated a public health outreach program to further improve engagement between traditional healers and local health centers to foster trust in the formal healthcare system and improve early identification and referral of patients with plaguelike symptoms, which can reflect numerous other infectious and noninfectious conditions. During 2010-2019, 65 traditional healers were involved in the outreach program; 52 traditional healers referred 788 patients to area health centers. The diagnosis was available for 775 patients; malaria (37%) and respiratory tract infections (23%) were the most common diagnoses. One patient had confirmed bubonic plague. Outreach to improve communication and trust between traditional healers and local healthcare settings may result in improved early case detection and intervention not only for plague but also for other serious conditions.

Efficacy of indoor residual spraying using lambda-cyhalothrin for controlling nontarget vector fleas (Siphonaptera) on commensal rats in a plague endemic region of northwestern Uganda.

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.

Evaluation and modification of off-host flea collection techniques used in northwest Uganda: laboratory and field studies.

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.

Epidemiology, Ecology and Prevention of Plague in the West Nile Region of Uganda: The Value of Long-Term Field Studies.

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.

Evaluation of rodent bait containing imidacloprid for the control of fleas on commensal rodents in a plague-endemic region of northwest Uganda.

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.

An Evaluation of the Flea Index as a Predictor of Plague Epizootics in the West Nile Region of Uganda.

Plague is a low incidence flea-borne zoonosis that is often fatal if treatment is delayed or inadequate. Outbreaks occur sporadically and human cases are often preceded by epizootics among rodents. Early recognition of epizootics coupled with appropriate prevention measures should reduce plague morbidity and mortality. For nearly a century, the flea index (a measure of fleas per host) has been used as a measure of risk for epizootic spread and human plague case occurrence, yet the practicality and effectiveness of its use in surveillance programs has not been evaluated rigorously. We sought to determine whether long-term monitoring of the Xenopsylla flea index on hut-dwelling rats in sentinel villages in the plague-endemic West Nile region of Uganda accurately predicted plague occurrence in the surrounding parish. Based on observations spanning ~6 yr, we showed that on average, the Xenopsylla flea index increased prior to the start of the annual plague season and tended to be higher in years when plague activity was reported in humans or rodents compared with years when it was not. However, this labor-intensive effort had limited spatial coverage and was a poor predictor of plague activity within sentinel parishes.

An Evaluation of Removal Trapping to Control Rodents Inside Homes in a Plague-Endemic Region of Rural Northwestern Uganda.

Rodents pose a significant threat to human health, particularly in rural subsistence farming communities in Africa, where rodents threaten food security and serve as reservoirs of human pathogens, including the agents of plague, leptospirosis, murine typhus, rat-bite fever, Lassa fever, salmonellosis, and campylobacteriosis. Our study focused on the plague-endemic West Nile region of Uganda, where a majority of residents live in Uganda government-defined poverty, rely on subsistence farming for a living, and frequently experience incursions of rodents into their homes. In this study, we show that rodent removal was achieved in a median of 6 days of intensive lethal trapping with multiple trap types (range: 0-16 days). However, rodent abundance in 68.9% of homesteads returned to pretreatment levels within a median of 8 weeks (range 1-24 weeks), and at least a single rodent was captured in all homesteads by a median of 2 weeks (range 1-16 weeks) after removal efforts were terminated. Results were similar between homesteads that practiced rodent control whether or not their neighbors implemented similar strategies. Overall, intensive lethal trapping inside homes appears to be effective at reducing rodent abundance, but control was short lived after trapping ceased.

Rat Fall Surveillance Coupled with Vector Control and Community Education as a Plague Prevention Strategy in the West Nile Region, Uganda.

Plague, primarily a disease of rodents, is most frequently transmitted by fleas and causes potentially fatal infections in humans. In Uganda, plague is endemic to the West Nile region. Primary prevention for plague includes control of rodent hosts or flea vectors, but targeting these efforts is difficult given the sporadic nature of plague epizootics in the region and limited resource availability. Here, we present a community-based strategy to detect and report rodent deaths (rat fall), an early sign of epizootics. Laboratory testing of rodent carcasses is used to trigger primary and secondary prevention measures: indoor residual spraying (IRS) and community-based plague education, respectively. During the first 3 years of the program, individuals from 142 villages reported 580 small mammal deaths; 24 of these tested presumptive positive for Yersinia pestis by fluorescence microscopy. In response, for each of the 17 affected communities, village-wide IRS was conducted to control rodent-associated fleas within homes, and community sensitization was conducted to raise awareness of plague signs and prevention strategies. No additional presumptive Y. pestis-positive carcasses were detected in these villages within the 2-month expected duration of residual activity for the insecticide used in IRS. Despite comparatively high historic case counts, no human plague cases were reported from villages participating in the surveillance program; five cases were reported from elsewhere in the districts. We evaluate community participation and timeliness of response, report the frequency of human plague cases in participating and surrounding villages, and evaluate whether a program such as this could provide a sustainable model for plague prevention in endemic areas.

Comparison of Zoonotic Bacterial Agents in Fleas Collected from Small Mammals or Host-Seeking Fleas from a Ugandan Region Where Plague Is Endemic.

Fleas (n = 407) were collected from small mammals trapped inside huts and surroundings of homesteads in five villages within the Arua and Zombo districts of Uganda. The most common flea species were Dinopsyllus lypusus (26%) and Xenopsylla cheopis (50%). Off-host fleas (n = 225) were collected inside huts by using Kilonzo flea traps. The majority of the off-host fleas were Ctenocephalides felis (80%). All fleas were examined for the presence of Bartonella spp., Rickettsia spp., and Yersinia spp. Bartonella DNA was detected in 91 fleas, with an overall prevalence of 14%. Bartonella prevalence was significantly higher in rodent or shrew fleas than in off-host fleas (22% versus 1%). The majority of Bartonella-positive fleas were of the species D. lypusus (61%), X. cheopis (20%), and Ctenophthalmus calceatus (14%). Sequencing analysis identified 12 Bartonella genetic variants, 9 of which belonged to the zoonotic pathogen B. elizabethae species complex. Rickettsia DNA was detected in 143 fleas, giving an overall prevalence of 23%, with a significantly higher prevalence in off-host fleas than in rodent or shrew fleas (56% versus 4%). The majority (88%) of Rickettsia-positive fleas were C. felis and were collected from Kilonzo traps, while a small portion (10%) were X. cheopis collected from rodents. Sequencing analysis identified six Rickettsia genogroups that belonged either to zoonotic R. felis or to the closely related "Candidatus Ricksettia asemboensis" and "Candidatus Ricksettia sengalensis." Yersinia DNA was not detected in the fleas tested. These observations suggested that fleas in northwestern Uganda commonly carry the zoonotic agents B. elizabethae and R. felis and potentially play an important role in transmitting these infections to humans. IMPORTANCE Fleas play critical roles in transmitting some infections among animals and from animals to humans. Detection of pathogens in fleas is important to determine human risks for flea-borne diseases and can help guide diagnosis and treatment. Our findings of high prevalence rates of B. elizabethae and R. felis in fleas in the Arua and Zombo districts of Uganda implicate these agents as potential causative agents of undiagnosed febrile illnesses in this area.

Seasonal fluctuations of small mammal and flea communities in a Ugandan plague focus: evidence to implicate Arvicanthis niloticus and Crocidura spp. as key hosts in Yersinia pestis transmission.

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.

Bartonella species in invasive rats and indigenous rodents from Uganda.

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.

Identification of risk factors for plague in the West Nile Region of Uganda.

Plague is an often fatal, primarily flea-borne rodent-associated zoonosis caused by Yersinia pestis. We sought to identify risk factors for plague by comparing villages with and without a history of human plague cases within a model-defined plague focus in the West Nile Region of Uganda. Although rat (Rattus rattus) abundance was similar inside huts within case and control villages, contact rates between rats and humans (as measured by reported rat bites) and host-seeking flea loads were higher in case villages. In addition, compared with persons in control villages, persons in case villages more often reported sleeping on reed or straw mats, storing food in huts where persons sleep, owning dogs and allowing them into huts where persons sleep, storing garbage inside or near huts, and cooking in huts where persons sleep. Compared with persons in case villages, persons in control villages more commonly reported replacing thatch roofing, and growing coffee, tomatoes, onions, and melons in agricultural plots adjacent to their homesteads. Rodent and flea control practices, knowledge of plague, distance to clinics, and most care-seeking practices were similar between persons in case villages and persons in control villages. Our findings reinforce existing plague prevention recommendations and point to potentially advantageous local interventions.

Blood meal identification in off-host cat fleas (Ctenocephalides felis) from a plague-endemic region of Uganda.

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.

Evidence that rodent control strategies ought to be improved to enhance food security and reduce the risk of rodent-borne illnesses within subsistence farming villages in the plague-endemic West Nile region, Uganda.

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.

Flea diversity as an element for persistence of plague bacteria in an East African plague focus.

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 (~725-1160 m) to higher elevation sites within the focus (~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.

Landscape and residential variables associated with plague-endemic villages in the West Nile region of Uganda.

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.

Flea diversity and infestation prevalence on rodents in a plague-endemic region of Uganda.

In Uganda, the West Nile region is the primary epidemiologic focus for plague. The aims of this study were to 1) describe flea-host associations within a plague-endemic region of Uganda, 2) compare flea loads between villages with or without a history of reported human plague cases and between sampling periods, and 3) determine vector loads on small mammal hosts in domestic, peridomestic, and sylvatic settings. We report that the roof rat, Rattus rattus, is the most common rodent collected in human dwellings in each of the 10 villages within the two districts sampled. These rats were commonly infested with efficient Y. pestis vectors, Xenopsylla cheopis and X. brasiliensis in Arua and Nebbi districts, respectively. In peridomestic and sylvatic areas in both districts, the Nile rat, Arvicanthus niloticus, was the most abundant rodent and hosted the highest diversity of flea species. When significant temporal differences in flea loads were detected, they were typically lower during the dry month of January. We did not detect any significant differences in small mammal abundance or flea loads between villages with our without a history of human plague, indicating that conditions during inter-epizootic periods are similar between these areas. Future studies are needed to determine whether flea abundance or species composition changes during epizootics when humans are most at risk of exposure.

Identification of flea blood meals using multiplexed real-time polymerase chain reaction targeting mitochondrial gene fragments.

Human plague is found in the West Nile region of Uganda and Democratic Republic of the Congo where flea vectors are often found inhabiting homes. We have developed a multiplexed, real-time polymerase chain reaction assay targeting mitochondrial genes that is capable of detecting blood meal sources in fleas collected off-host in East Africa. Laboratory tests showed that the assay is specific for the intended targets and has a detection limit below one picogram of DNA. Testing of wild-caught fleas from the Democratic Republic of Congo suggests that humans are at significant risk from flea-borne disease and implicates domestic animals including cats, chickens, and the black rat as potential sources of human exposure to fleas and flea-borne diseases. Future application of the assay will help us better define the ecology of plague in East Africa to implement effective control measures to combat the spread of disease.