Specimens and methods

Animal specimens were collected with the approval of the Cameroonian Ministry of Livestock Fisheries and Animal Industries within the framework of the rabies diagnosis in Cameroon. Specimens analyzed were obtained by convenience sampling since there is no system in place to actively collect animal specimens from the veterinary networks for rabies diagnosis in Cameroon. Thus, passive surveillance during 2010–2013 was maintained by veterinarians and animal health officers who sent specimens from animals that expressed rabies symptoms, appeared sick and/or had bitten someone, for rabies testing at CPC. The entire head of the suspected animals were sent frozen to CPC where the brain was extracted, kept at +4°C and tested within 48 h.

Detection of rabies nucleocapsid was performed on the brain postmortem biopsy by fluorescent antibody test (FAT) using rabbit IgG against RABV nucleocapsid (Bio-Rad, Marnes-la Coquette, France) as previously described [7]. The negative FAT results were further confirmed by virus isolation which was performed by inoculation into Murina neuroblastoma cell cultures as described elsewhere [7].

Geographic origin of the specimens

Geographic and overtime distribution of positive samples

Overall, 74.2% (66/89) of brain specimens from dogs were found rabies-positive using FAT while specimens from the monkey and pig were tested negative (Table 1). Moreover, virus isolation was negative for all 25 specimens whose FAT was initially negative. The percentage of positive specimens varied across the 4-years period from 65.5 % (19/29) in 2010 to 90.9% (20/22) in 2012 (Figure 2). The numbers of specimens submitted for diagnosis were very low to estimate the actual rate and the seasonal pattern of dog rabies. However, dog rabies was laboratory confirmed in 3 regions of the southern regions of Cameroon including Centre, West and North West (Figure 1). Concerning the capital city Yaoundé in particular, 78.2% (36/46) of specimens were tested positive for RABV antigen: 7, 3, 15, and 11 specimens in 2010, 2011, 2012 and 2013 respectively. These data provide evidence of the risk of rabies acquisition from dog bites in at least some areas of Cameroon including the nation capital despite increasing awareness and efforts towards rabies control.

The percentage of rabies-infected dogs over the 2010–2013 period (74.2%; 66/89) was apparently higher than the one reported during the 1990–1999 period (45.8%; 330/721) [6]. The higher frequency in this study may be due to the fact that most specimens were sampled in Yaounde and where thus sent to the laboratory in good conditions. This difference may also be due to more accurate clinical diagnosis by veterinarians/and technicians in the field. As previously reported in Cameroon [6], dog rabies seemed to be more frequent in the urban areas than rural areas. However, this observation could be a result of a bias caused by the poor accessibility to the diagnostic laboratory at CPC and also the lack of knowledge of the rural population about dog rabies. There is a need of increased sensitization of the population, especially in rural areas, about the rabies risk. Another factor that may have account for underestimation of dog rabies in rural areas is the affordability of sample shipment from periphery levels to the CPC laboratory at the central level. Furthermore, the fact that dog owners have to pay for the treatment of bitten individuals constitutes a factor of underreporting to the local health authorities. As reported in other African countries [5, 8], reporting bias, lack of sample submission from distant regions especially rural areas and the lack of awareness campaigns may have resulted to the underestimation of the overall rate of dog rabies in the southern Cameroon.

Despite the main intervention of animal health authorities through mass vaccination campaigns of dogs and cats against rabies launched regularly on the international rabies day, dog rabies remains a threat to human health in Cameroon. Theses campaigns have not been as effective as expected from previous reports [9, 10]. Till now, interventions for the prevention of human rabies through dog rabies control have been based on very limited data generated from passive surveillance. To be more effective future vaccination campaigns against dog rabies need to be accompanied by a scientific evaluation in the light of data generated from an active rabies surveillance system and further field studies. In particular, these later should address the specific gaps in the knowledge about the awareness of the human populations, dog demography and ecology as well as the optimal timing and periodicity of vaccination campaigns.

Ethical approval

Not required. Animal specimens were collected with the approval of the Cameroonian Ministry of Livestock, Fisheries and Animal Industries within the frame of the rabies surveillance in Cameroon.