Fever and malaria in highland Uganda

Sensitivity of fever for diagnosis of clinical malaria in a Kenyan area of unstable, low malaria transmission

Background

Malaria in highland areas of Kenya affects children and adults. Local clinicians include symptoms other than fever when screening for malaria because they believe that fever alone does not capture all cases of malaria.

Methods

Individuals who presented to dispensaries in a highland Kenya site of low, unstable malaria transmission from 2007–2011 with 1 or more of 11 symptoms were tested by microscopy for malaria. Clinical malaria was defined as asexual Plasmodium falciparum infection on peripheral blood smear in an individual with any screening symptom. Asymptomatic P. falciparum infection was assessed in a cohort at ten time points to determine the extent to which symptomatic episodes with parasitaemia might be attributable to baseline (asymptomatic) parasitaemia in the community.

Results

3,420 individuals were screened for malaria, 634 < 5 years of age and 2,786 ≥ 5 years of age. For the diagnosis of clinical malaria, the symptom of fever had a sensitivity and specificity of 88.9% and15.4% in children <5 years, and 55.8% and 54.4% in children ≥5 years, respectively. Adding the symptom of headache increased sensitivity to 94. 4% in children <5 years and 96.8% in individuals ≥5 years, but decreased specificity to 9.9% and 11.6%, respectively, and increased the number of individuals who would be tested by 6% and 92%, respectively. No combination of symptoms improved upon the presence fever or headache for detection of clinical malaria. In the cohort of asymptomatic individuals, P. falciparum parasitaemia was infrequent (0.1%).

Conclusion

In areas of low, unstable malaria transmission, fever is a sensitive indicator of clinical malaria in children <5 years, but not in older children and adults. Adding headache to fever as screening symptom increases sensitivity of detection in individuals ≥5 years old at the cost of decreased specificity. Screening for symptoms in addition to fever may be required to accurately capture all cases of clinical malaria in individuals ≥5 years old in areas of low malaria transmission.

Development of clinical immunity to malaria in highland areas of low and unstable transmission

In highland areas of unstable, low malaria transmission, the extent to which immunity to uncomplicated malaria develops with age and intermittent parasite exposure has not been well characterized. We conducted active surveillance for clinical malaria during April 2003-March 2005 in two highland areas of western Kenya (Kapsisiywa and Kipsamoite). In both sites, annual malaria incidence was significantly lower in persons ≥ 15 years of age than in persons < 5 years of age (Kapsisiywa: incidence = 382.9 cases/1,000 persons among persons < 1-4 years of age versus 135.1 cases/1,000 persons among persons ≥ 15 years of age; Kipsamoite: incidence = 233.0 cases/1,000 persons in persons < 1-4 years of age versus 43.3 cases/1,000 persons in persons ≥ 15 years of age). In Kapsisiywa, among persons with malaria, parasite density and axillary body temperature were also significantly lower in persons ≥ 15 years of age than in persons < 5 years of age. Even in highland areas of unstable and low malaria transmission, age is associated with development of clinical immunity to malaria.

Malaria Knowledge, Concern, Land Management, and Protection Practices among Land Owners and/or Managers in Lowland versus Highland Ecuador

To control malaria effectively, it is essential to understand the current knowledge, beliefs, concerns, land management practices, and mosquito bite protection methods in use by citizens. This study presents a comparative, quantitative, interview-based study of land owners and/or managers (n = 262) in the Ecuadorian lowlands (presently considered malarious) (n = 131) and highlands (potentially malarious in the future) (n = 131). Although respondents had a strong understanding of where the disease occurs in their own country and of the basic relationship among standing water, mosquitoes, and malaria, about half of respondents in potential risk areas denied the current possibility of malaria infection on their own property. As well, about half of respondents with potential anopheline larval habitat did not report its presence, likely due to a highly specific definition of suitable mosquito habitat. Most respondents who are considered at risk of malaria currently use at least one type of mosquito bite prevention, most commonly bed nets.

Regime shifts and heterogeneous trends in malaria time series from Western Kenya Highlands

Large malaria epidemics in the East African highlands during the mid and late 1990s kindled a stream of research on the role that global warming might have on malaria transmission. Most of the inferences using temporal information have been derived from a malaria incidence time series from Kericho. Here, we report a detailed analysis of 5 monthly time series, between 15 and 41 years long, from West Kenya encompassing an altitudinal gradient along Lake Victoria basin. We found decreasing, but heterogeneous, malaria trends since the late 1980s at low altitudes (<1600 m), and the early 2000s at high altitudes (>1600 m). Regime shifts were present in 3 of the series and were synchronous in the 2 time series from high altitudes. At low altitude, regime shifts were associated with a shift from increasing to decreasing malaria transmission, as well as a decrease in variability. At higher altitudes, regime shifts reflected an increase in malaria transmission variability. The heterogeneity in malaria trends probably reflects the multitude of factors that can drive malaria transmission and highlights the need for both spatially and temporally fine-grained data to make sound inferences about the impacts of climate change and control/elimination interventions on malaria transmission.