Plague in Lushoto district, Tanzania, 1980-1988

Knowledge and practices related to plague persistence in plague-endemic foci, Mbulu District, Tanzania

INTRODUCTION

Plague continues to be a major public health concern in African countries. Several social practices and environmental conditions have been associated with the reoccurrence of bubonic plague, especially in places where the disease is prevalent. Therefore, it remains important to understand people knowledge, behavior and practices related to disease risks in order to identify factors that may hinder prevention and control strategies in the foci.

METHODS AND RESULTS

A study survey of 100 households was conducted in Mbulu district to assess plague knowledge, factors that influence flea bite and measures used for rodent and flea control. Majority of participants (86%) were familiar with the plague disease and about (50%) mentioned swelling lymph nodes as a common symptom. Most of the participants (62%) claimed to observe human plague cases during the long rain season. The majority of participants (97%) reported to experience flea bite in their domestic settings, with most stating that they experienced more flea bites during the dry season. Houses with livestock had a greater likelihood of flea bite (OR = 2.7; 95% CI: 0.36-18.80, p = 0.267) compared to houses with no livestock. Furthermore, residents reported using both local and chemical methods to control rodents and flea inside houses. Most respondents preferred using local methods in flea control. Respondents stated that the efficacy of flea control methods being applied ranged from few days to several months. There was limited knowledge of the residual effects of the agricultural chemicals being used to control fleas among the surveyed community.

CONCLUSION

Our study highlights the importance of raising awareness and adopting effective control methods for controlling fleas and lower the risk of plague transmission and other flea borne diseases in the local communities. Sensitization of the local community on the use of appropriate chemicals for flea control is urgent to avoid any potential long-term impacts of the residual effects on the health of the local communities.

Plague in Tanzania: first report of sylvatic plague in Morogoro region, persistence in Mbulu focus, and ongoing quiescence in Lushoto and Iringa foci

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Six (0.93%) rodents carried antibodies against Yersinia pestis fraction 1 antigens.

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There is evidence of Y. pestis circulation in small mammals in Morogoro.

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Plague continues to persist in small mammals in Mbulu.

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There is ongoing quiescence in Lushoto and Iringa plague foci.

Objectives

Plague has been a threat to human health in Tanzania since 1886. This zoonotic disease has established several endemic foci in the country, posing a risk of outbreaks. This study was conducted to investigate the presence of Yersinia pestis in small mammals in five districts. These districts were selected because of recent (Mbulu), past (40-18 years ago: Lushoto) and historic (>100 years ago: Iringa and Kilolo) human cases of plague. In addition, one region that has not had any reported human cases of plague was included (Morogoro-Mvomero).

Methods

Blood from 645 captured small mammals was screened for antibodies against the fraction 1 (F1) antigen of Y. pestis using indirect enzyme-linked immunosorbent assay (ELISA) and competitive-blocking ELISA.

Results

Specific antibodies against Y. pestis F1 antigens were detected in six (0.93%) animals belonging to Mastomys natalensis. Of these, four animals were captured in the active focus in Mbulu, and two animals were captured from an area with no history of human plague (Morogoro-Mvomero).

Conclusion

These results provide evidence of the circulation of Y. pestis in small mammals in Tanzania. Furthermore, evidence of the circulation of Y. pestis in Morogoro-Mvomero highlights the importance of carrying out plague surveillance in areas with no history of human plague, which can help to predict areas where future outbreaks may occur.

Plague and the human flea, Tanzania

Pulex irritans fleas were more common in villages with high plague incidence.

Domestic fleas were collected in 12 villages in the western Usambara Mountains in Tanzania. Of these, 7 are considered villages with high plague frequency, where human plague was recorded during at least 6 of the 17 plague seasons between 1986 and 2004. In the remaining 5 villages with low plague frequency, plague was either rare or unrecorded. Pulex irritans, known as the human flea, was the predominant flea species (72.4%) in houses. The density of P. irritans, but not of other domestic fleas, was significantly higher in villages with a higher plague frequency or incidence. Moreover, the P. irritans index was strongly positively correlated with plague frequency and with the logarithmically transformed plague incidence. These observations suggest that in Lushoto District human fleas may play a role in plague epidemiology. These findings are of immediate public health relevance because they provide an indicator that can be surveyed to assess the risk for plague.

Animals as sentinels of bioterrorism agents

Pets, wildlife, or livestock could provide early warning.

We conducted a systematic review of the scientific literature from 1966 to 2005 to determine whether animals could provide early warning of a bioterrorism attack, serve as markers for ongoing exposure risk, and amplify or propagate a bioterrorism outbreak. We found evidence that, for certain bioterrorism agents, pets, wildlife, or livestock could provide early warning and that for other agents, humans would likely manifest symptoms before illness could be detected in animals. After an acute attack, active surveillance of wild or domestic animal populations could help identify many ongoing exposure risks. If certain bioterrorism agents found their way into animal populations, they could spread widely through animal-to-animal transmission and prove difficult to control. The public health infrastructure must look beyond passive surveillance of acute animal disease events to build capacity for active surveillance and intervention efforts to detect and control ongoing outbreaks of disease in domestic and wild animal populations.

Preliminary observations on factors responsible for long persistence and continued outbreaks of plague in Lushoto district, Tanzania

Human plague has been an important public health problem in Tanzania for over a century. Recorded outbreaks of the disease have been reported from various parts of Tanzania, including Iringa, Kagera, Singida, Mbulu, Arusha and Kilimanjaro since 1886. Since 1980 however, only Lushoto, Singida and Karatu districts have experienced outbreaks of the disease. Of these areas, Lushoto has disproportionately high incidences of the disease and this has persisted for nearly 17 years. Efforts to curb the disease through conventional methods, including control of vectors and reservoirs, chemotherapy and chemoprophylaxis, enforcement of sanitation improvement as well as health education, have been applied every year, but plague cases and deaths continue to occur in the area to date. During the period April 1980 to December 1996, a total of 6599 cases with 580 (8.8%) deaths were recorded. Biological factors, such as the presence of suitable rodent reservoirs, efficient flea vectors and plague bacillus, could be partly responsible for the long persistence and recurrence of the disease. Since such factors are also common in other plague foci where the disease has never been persistently recurrent, and where indigenous people are culturally different from those in Lushoto, it is assumed that socio-cultural factors play an important role as determinants of the disease in the latter district. This paper reports preliminary observations on socio-cultural, biological and environmental factors which are thought to be, at least partly, responsible for the long persistence and repeated outbreaks of plague in the district. These include traditional beliefs on the cause and health seeking behaviour for treatment of plague, sleeping and food storage habits, large populations of rodents and fleas, and status of the immediate environment.