Chikungunya Outbreak in Country with Multiple Vectorborne Diseases, Djibouti, 2019–2020

During 2019–2020, a chikungunya outbreak occurred in Djibouti City, Djibouti, while dengue virus and malaria parasites were cocirculating. We used blotting paper to detect arbovirus emergence and confirm that it is a robust method for detecting and monitoring arbovirus outbreaks remotely.


DISPATCHES
D jibouti is a semi-arid country bordered by Er- itrea, Somalia, and Ethiopia.In the region, the main vector of chikungunya virus (CHIKV) and dengue virus (DENV) is the Aedes aegypti mosquito.The French Armed Forces are stationed in Djibouti City, where 70% of the country's population live (total population ≈900,000).Military bases and housing are located in the urban area, and the entire French Defense Community (FDC), including service members, families, and civilian employees, comprise a population of 2,700.
During July-October 2019, a large-scale chikungunya outbreak (41,162 suspected cases, 16 laboratory-confirmed cases, attack rate 12.3%) occurred in Dire Dawa, Ethiopia, 260 km from Djibouti City (Appendix Figure, https://wwwnc.cdc.gov/EID/article/29/4/22-1850-App1.pdf) (1).In a 2010-2011 survey in Djibouti City, although no epidemic has been reported since, 2.6% of the population had serologic evidence of CHIKV infection (2).Given the road, rail, and air connections between the 2 cities and the CHIKV-naive local populations, we estimated the likelihood of a CHIKV outbreak in Djibouti City to be highly probable.Patient management was challenging because dengue fever and malaria are endemic to Djibouti (3).
We describe the comprehensive response implemented by the FDC to these multiple vectorborne diseases and evaluated the use of blood on blotting paper for arboviral diagnosis.With the consent of patients, we collected and anonymized epidemiologic and clinical data for diagnostic purposes.According to French regulations, because this outbreak was considered an immediate threat to public health, ethics approval was not required for this investigation.

The Study
In October 2019, we strengthened epidemiologic surveillance in the FDC to detect CHIKV emergence.We defined a suspected case of arboviral-like disease (ALD) as fever or chills and/or acute arthralgia and/ or rash and/or vomiting and diarrhea.Symptomatic patients were encouraged to seek medical care for systematic testing for dengue, chikungunya, and malaria.From each person with ALD signs/symptoms, we collected venous blood, spotted it onto Whatman 3MM blotting paper (Sigma-Aldrich, https://www.sigmaaldrich.com),dried the samples at room temperature, and stored them in a sealed plastic pouch
for preservation and transport (4).The National Reference Center for arboviruses in France performed reverse transcription PCR (RT-PCR) and serologic testing for CHIKV and DENV on blotting paper as described elsewhere (5).In January, equipment was set up locally to perform in-house RT-PCR for DENV and CHIKV on whole-blood samples (Figure 1) (6,7).Chikungunya cases were confirmed by positive RT-PCR on whole blood or blotting paper or by detection of CHIKV IgM on blotting paper.Dengue cases were confirmed by a positive DENV RT-PCR on whole blood or blotting paper or a positive nonstructural protein 1 (NS1) antigen rapid diagnostic test (RDT) (Bioline Dengue Duo; Abbott, https:// www.abbott.com).We provided care according to the French National Recommendations (8) and World Health Organization guidelines (9).Concurrently, we strengthened the following in the FDC vector-control measures and personal protection: larval source management, long clothing, insect repellents, and longlasting insecticidal nets.
DENV and CHIKV RT-PCR testing were performed both on whole blood and on blotting paper for 44.7% (51/114) (Tables 1, 2).Compared with RT-PCR of whole blood, no RT-PCR of blotting paper produced false-positive results.

Conclusions
Despite recent improvement in diagnostic tools, chikungunya outbreaks in Africa are probably underreported (11).During 2019-2020, a large-scale chikungunya outbreak occurred in Djibouti City (12).However, because of lack of diagnostic tests and dedicated reporting, no data are available to estimate its extent.The chikungunya outbreak remained limited (attack rate 2.1%) in the FDC but was followed by a dengue outbreak.We found that clinical features are helpful but not sufficient to discriminate between chikungunya and dengue (13,14).Biological confirmation remains necessary for determining appropriate care.The use of blood samples on blotting paper has been described as a field method for detecting arboviruses (4,5), routinely used in the French Armed Forces when deployed in Africa (15).In this study, we used blood samples on blotting paper to detect emergence of CHIKV and monitor the course of the outbreaks.Blotting paper provided a robust method for blood sampling and transport to a reference laboratory, making it possible to confirm 90% of the arboviral diagnoses.We recommend blotting paper as a field tool to detect and monitor arboviral epidemics remotely.Ben Taylor, cover artist for the August 2018 issue of EID, discusses how his personal experience with the Loa loa parasite influenced this painting.

Figure 1 .
Figure 1.Flowchart for arboviral-like disease diagnoses among French Defense Community in Djibouti, 2019-2020.*Number of samples tested was limited because RT-PCR of whole blood was introduced in Djibouti City 1 month after the start of the chikungunya outbreak.Ag, antigen; NS1, nonstructural protein 1; RT-PCR, reverse transcription PCR.
Seeing a several-centimeters-long worm traversing the conjunctiva of an eye is often the moment when many people realize they are infected with Loa loa, commonly called the African eyeworm, a parasitic nematode that migrates throughout the subcutaneous and connective tissues of infected persons.Infection with this worm is called loiasis and is typically diagnosed either by the worm's appearance in the eye or by a history of localized Calabar swellings, named for the coastal Nigerian town where that symptom was initially observed among infected persons.Endemic to a large region of the western and central African rainforests, the Loa loa microfilariae are passed to humans primarily from bites by flies from two species of the genus Chrysops, C. silacea and C. dimidiate.The more than 29 million people who live in affected areas of Central and West Africa are potentially at risk of loiasis.

Table 1 .
Chikungunya cases confirmed by RT-PCR (n = 57/58) of blood samples, WB or BP, among 114 confirmed cases of arboviral *RT-PCR tests were performed from October 2019 on dried blood spots stored on BP at the French National Reference Center for arboviruses in France.From January 2020, RT-PCR tests were also locally performed on WB samples at the French military medical center in Djibouti.BP, blotting paper; NA, not available (samples or result missing); RT-PCR, reverse transcription PCR; WB, whole blood.