**8. Geographic distribution and map**

Chikungunya fever has an epidemiological pattern with both sporadic cases and epidemics in west Africa, from Senegal to Cameroun, and in many other African countries (Democratic Republic of Congo, Nigeria, Angola, Uganda, Guinea, Malawi, Central African Republic, Burundi, and South Africa). Moreover, many epidemics occurred in Asia (Burma, Thailand, Cambodia, Vietnam, India, Sri Lanka, Timor, Indonesia, and the Philippines) in the 1960s and in the 1990s (Jain et al., 2008; Pialoux et al., 2007).

Major epidemics appear and disappear cyclically, usually with an inter-epidemic period ranging from 7 to 20 years. The huge outbreak that increased concern about CHIKV started in Kenya in 2004, where the seroprevalence rates reached 75% in Lamu island (Pialoux et al., 2007), before reaching the Comores, Seychelles, and Mauritius islands. The virus reached La Reunion island, a French overseas district, in March–April 2005, probably as a result of importation of cases among immigrants from the Comores. The outbreak had two phases: after some thousands of cases which occurred in March-April 2005, very few cases were reported during the austral winter, while the second epidemic peak arose in the initial months of 2006. For the first time, a substantial number of deaths (254) were attributed, directly or indirectly, to CHIKV. From late 2005 onwards, hospitals in some Indian states found themselves swamped with patients complaining of fever and joint pain, which turned out to be Chikungunya fever (Fusco et al., 2010). The World Health Organization Regional Office for South-East Asia has reported that 151 districts in nine states/provinces of India have been affected by Chikungunya fever between February and October 2006 (Pialoux et al., 2007).

Several imported cases were reported in industrialized countries among travellers returning from endemic areas, mainly tourists and immigrants (Depoortere & Coulombier, 2006). In particular, many cases were detected in early 2006, when the outbreak involved the Indian Ocean islands. The Indian Ocean islands, India, and Malaysia are popular tourist destinations. According to the World Tourism Organization, an estimated 1 474 218 people travelled from Madagascar, Mauritius, Mayotte, Reunion, and the Seychelles to European countries in 2004 (Depoortere & Coulombier, 2006; Parola et al., 2006).

The European country with the highest number of imported cases was France, especially the south-eastern region of Provence-Alpes-Côte d'Azur, and Marseille in particular, home to a large Comorian community (Cordel et al., 2006; Hochedez et al., 2007). Other European countries that reported imported cases include Belgium, Bosnia, Czech Republic, Croatia,

scale prevention campaigns using DDT have been effective against *A. aegypti* but not *A. albopictus*. Control of *A. aegypti* has rarely been achieved and never sustained (Reiter et al., 2006). Recent data show the different degrees of insecticide resistance in *A. albopictus* and *A. aegypti* (Cui et al., 2006). However, vector control is an endless, costly, and labour-intensive measure and is not always well accepted by local populations, whose cooperation is crucial. Control of CHIKV infection, other than use of drugs for treatment of disease, development of vaccines, individual protection from mosquitoes and vector control programs, also involves surveillance that is fundamental for early identification of cases and quarantine measurement. A model used in investigation of the transmission potential of CHIKV in Italy has proven useful to provide insight into the possible impact of future outbreaks in temperate climate regions and the effectiveness of the interventions performed during the

Chikungunya fever has an epidemiological pattern with both sporadic cases and epidemics in west Africa, from Senegal to Cameroun, and in many other African countries (Democratic Republic of Congo, Nigeria, Angola, Uganda, Guinea, Malawi, Central African Republic, Burundi, and South Africa). Moreover, many epidemics occurred in Asia (Burma, Thailand, Cambodia, Vietnam, India, Sri Lanka, Timor, Indonesia, and the Philippines) in the 1960s

Major epidemics appear and disappear cyclically, usually with an inter-epidemic period ranging from 7 to 20 years. The huge outbreak that increased concern about CHIKV started in Kenya in 2004, where the seroprevalence rates reached 75% in Lamu island (Pialoux et al., 2007), before reaching the Comores, Seychelles, and Mauritius islands. The virus reached La Reunion island, a French overseas district, in March–April 2005, probably as a result of importation of cases among immigrants from the Comores. The outbreak had two phases: after some thousands of cases which occurred in March-April 2005, very few cases were reported during the austral winter, while the second epidemic peak arose in the initial months of 2006. For the first time, a substantial number of deaths (254) were attributed, directly or indirectly, to CHIKV. From late 2005 onwards, hospitals in some Indian states found themselves swamped with patients complaining of fever and joint pain, which turned out to be Chikungunya fever (Fusco et al., 2010). The World Health Organization Regional Office for South-East Asia has reported that 151 districts in nine states/provinces of India have been affected by Chikungunya fever between February and October 2006 (Pialoux et

Several imported cases were reported in industrialized countries among travellers returning from endemic areas, mainly tourists and immigrants (Depoortere & Coulombier, 2006). In particular, many cases were detected in early 2006, when the outbreak involved the Indian Ocean islands. The Indian Ocean islands, India, and Malaysia are popular tourist destinations. According to the World Tourism Organization, an estimated 1 474 218 people travelled from Madagascar, Mauritius, Mayotte, Reunion, and the Seychelles to European

The European country with the highest number of imported cases was France, especially the south-eastern region of Provence-Alpes-Côte d'Azur, and Marseille in particular, home to a large Comorian community (Cordel et al., 2006; Hochedez et al., 2007). Other European countries that reported imported cases include Belgium, Bosnia, Czech Republic, Croatia,

countries in 2004 (Depoortere & Coulombier, 2006; Parola et al., 2006).

outbreak (Poletti et al., 2011).

al., 2007).

**8. Geographic distribution and map** 

and in the 1990s (Jain et al., 2008; Pialoux et al., 2007).

Germany, Greece, Italy, Serbia, Spain, Switzerland, Norway, and the United Kingdom (Beltrame, A. 2007; Deporteere & Coulombier, 2006; Fusco, F.M. 2006; Pialoux et al., 2007; Taubitz et al., 2007). In 2006, CHIK fever cases have also been reported in traveller returning from known outbreak areas to Canada, the Caribbean (Martinique), and South America (French Guyana). During 2005-2006, 12 cases of CHIK fever were diagnosed serologically and virologically at CDC in travellers who arrived in the United States from areas known to be epidemic or endemic for CHIK fever, and 26 additional imported cases with onset in 2006 underscores the importance of recognizing such cases among travellers (CDC, 2006; CDC 2007).

Moreover, CHIKV gave rise in 2007 to the first autochthonous European outbreak in Italy, in the northern region of Emilia-Romagna (Rezza et al*.,* 2007; Charrel et al., 2008).

In June 2007, an Indian citizen returned to Italy after a visit to relatives in Kerala, India, developed 2 episodes of fever. During the second febrile episode, he visited his cousin in Castiglione di Cervia. The cousin had an onset of symptoms, with fever and arthralgia, on July 4. This sequence of events started the first Chikungunya fever outbreak in a temperate country, that lasted approximately 2 months with a total 247 cases of Chikungunya fever occurred in the region (217 laboratory-confirmed, 30 suspected) (Fusco et al., 2010). A unique sequence of events seems to have contributed to the establishment of local transmission in Emilia-Romagna: the high concentration of competent vectors *A. albopictus*  in the area at the time of arrival of the index case, the presence of a sufficient human population density and the temporal overlapping of arthropod activity (seasonal syncronicity) (Charrel et al., 2008; Rezza et al*.,* 2007).

During 2008, cases of Chikungunya fever have been reported from many countries in Asia other than India, as well as active epidemics from Singapore, Sri Lanka, and Malaysia (Leo et al., 2009).

Since 2006, the Regional Office of the French Institute For Public Health Surveillance in the Indian Ocean has conducted epidemiological and biological surveillance for CHIKV infection. During the period December 2006-July 2009, no confirmed case was detected on Reunion Island and Mayotte, but new outbreaks were reported in Madacascar. After few years of relative dormancy in Réunion Island, in August 2009, a cluster of cases was identified on the western coast of Réunion Island (D'Ortenzio et al., 2009) and, subsequently, an outbreak of CHIKV infection was described on Réunion Island in 2010 (D'Ortenzio et al., 2011). Moreover, recent publications described cases of Chikungunya fever in tourist returning from Maldives, confirming the circulation of the virus by the end of 2009 (Pfeffer et al., 2010; Receveur et al., 2010)

These episodes have refreshed the concerns about the possibility of renewed autochthonous transmission in Mediterranean countries and highlight the need for surveillance in countries where emerging infections may be introduced by returning travellers. Travellers can serve as sentinel population providing information regarding the emergence or re-emergence of an infectious pathogen in a source region. Travellers can thus act as carriers who inadvertently ferry pathogens that can be used to map the location, dynamics and movement of pathogenic strains (Pistone et al, 2009). Thus, with the increase in intercontinental travel, travellers can provide insights into the level of the risk of transmission of infections in other geographical regions.

The geographic range of CHIKV is mainly in Africa and Asia (Fig. 1)

The Re-Emergence of an Old Disease: Chikungunya Fever 127

et al., 2007; Vazeille et al., 2007), that, in turn, may expand the potential for CHIKV to diffuse to the Americas and Europe, due to the widespread distribution of this vector, in particular in Italy (Knudsen, 1995). In a previous paper we characterized 7 viral isolates (5 imported and 2 autochthonous cases), with respect to the molecular signatures of the Indian Ocean Outbreak in E1, particularly the A226V mutation. Imported cases included 3 returning from Mauritius in 2006 and 2 returning from India in 2006 and 2007, respectively; the autochthonous cases occurred during the 2007 Italian outbreak (Bordi et al., 2008). CHIKV sequences of a 1013 bp fragment of E1 gene (nucleotide positions 10145-11158, respect to the

All 7 isolates carried the M269V and D284E Indian Ocean signatures while the A226V mutation was present in all the isolates imported from Mauritius, in the autochthonous cases from the Italian outbreak and in the isolate imported from India in 2007, but was

Our findings indicated that, during 2006 and 2007, multiple strains have been imported to Italy from countries where explosive Chikungunya outbreaks were ongoing. All the strains isolated in Italy, both imported and autochthonous, displayed two molecular signatures of

Indian Ocean

Central Africa

**Central/east African genotype Africa** 

**Asia** 

**West** 

Fig. 2. Phylogenetic tree of CHIKV strains performed on partial E1 gene

cases in Italy are in bold (Bordi et al., Clin Infect Dis*,* 2008)

CHIKV sequences of a 1013 bp fragment of E1 gene (nucleotide positions 10145-11158, respect to the reference strain S27) have been analyzed. The strains isolated from human

reference strain S27) have been analyzed (Fig.2).

absent in the case imported from India in 2006.

Fig. 1. Geographical distribution of CHIKV shown in the most recent map coming from the CDC's Traveler's Health website (http://wwwn.cdc.gov/travel/default.aspx).
