Economic impact and prevalence
Heartwater is one of the main tickborne diseases together with theileriosis and trypanosomosis in tropical countries. For the Southern Africa Development Community (Angola, Botswana, Malawi, Mozambique, South Africa, Swaziland, Tanzania and Zimbabwe) the losses are estimated around 47.6 millions of dollars per year. Important losses are due to mortality, diminution o
f productivity in farming systems and cost of treatment (use of antibiotics and acaricides). It is a major, and in some instances, the most important obstacle against introducing high producing animals into Africa with the aim of upgrading or replacing local stock (Uilenberg, 1982a). It is a major disease problem when local animals are, usually for the sake of grazing, moved from heartwater-free to heartwater-infected areas (Neitz, 1967). It remains a problem and a threat in endemic areas especially amongst small stock (Thomas and Mansvelt, 1957). The effect of dipping and environmental changes influences endemic stability, which is often difficult or impossible to manipulate (Bezuidenhout and Bigalke, 1987). The development of molecular diagnostic tools allows a better estimation of the prevalence of heartwater thanks to detection both in organs from suspected dead ruminants and in ticks. ruminantium prevalence in ticks by pCS20 nested PCR has been evaluated from 3 to 10% depending on the year of tick samplings (Dr Hassane Adakal, personal communication, Adakal et al., 2010b). Moreover, a study evaluating the efficiency of the inactivated vaccine in field conditions in Burkina Faso allowed identifying the impact of heartwater on susceptible ruminants. In this study, two successive trial assays on susceptible imported sahelian sheep demonstrated that 51% and 53% of unvaccinated sheep died from heartwater (Adakal et al., 2010a). In the Gambia, the seroprevalence rate per site in small ruminants varied from 6.9% and 100% (5 regions) (Faburay et al., 2005). ruminantium infected Amblyomma ticks collected on 15 different sites, varied strongly from 1.6 to 15.1% depending on the site of sampling (Faburay et al., 2007a). These results showed a gradient risk of increasing heartwater from the East to the West of the Gambia. In Nigeria a study done in 2011 on 7 sites in the south of Nigeria shows a 9.6% of E. ruminantium tick prevalence (Personal communications, Dr Maxwell Opara). In the Caribbean region, only Guadeloupe and Antigua are infected with heartwater. In Guadeloupe, the E. ruminantium tick prevalence is higher (i.e. 19.1% in Marie Galante with 73.8% of herds infested) compared to Antigua 5.8% of E.ruminantium infected ticks with only 2.2% of herds infested (Vachiéry et al., 2008b). These islands still represent a reservoir for ticks and heartwater in the Caribbean. It is a threat to areas such as the American mainland due to migratory birds potentially carrying infected ticks from the Caribbean area where the disease is present. Moreover, potential vectors are present but do not harbour the disease (Uilenberg, 1982b; Uilenberg et al., 1984). It is also a threat to countries where the vectors may be introduced and become established (Wilson and Richard, 1984; Barré et al., 1987). It will therefore probably remain a disease of major importance until an effective and safe vaccine becomes available. This disease is on the list of diseases notifiable to the World Organisation for Animal Health (OIE). The distribution section contains data from OIE's WAHID database on disease occurrence. For further information on this disease from OIE, see the website: www.oie.int
