Figure

Figure. . Areas in northwestern Tanzania where seroprevalence of antibodies to peste des petits ruminants virus (PPRV) was studied in cattle and buffalo. Cattle were sampled in 2011; all had been alive...

Serum samples from cattle living in close proximity to sheep and goats were available as part of epidemiologic studies involving randomly selected pastoralist households in Ngorongoro District, an area of the Serengeti ecosystem in northern Tanzania where the 2008 PPR outbreak had been confirmed (Figure) (7). The sampling was conducted in early to mid-2011 and included serum samples from cattle >3 years of age (as determined on the basis of incisor tooth eruption) and from cattle <2 years of age; the older cattle were alive during the 2008 outbreak, and the younger cattle were born after the outbreak (Table 1). In the area, large-scale PPR vaccination of sheep and goats was initiated in early 2011 but did not include cattle. The last rinderpest vaccination campaign in Tanzania was carried out in 1997 (13).

Serum samples from buffalo (Syncerus caffer) and gazelle (Eudorcas thomsonii and Nanger granti) came from an archived serum bank and were made available through the Tanzania Wildlife Research Institute–Messerli Foundation Wildlife Veterinary Programme in Seronera, Tanzania. The samples had been collected during wildlife immobilization operations conducted for rinderpest surveillance, research activities, and conservation management (Table 2). Wildlife samples originated from several ecosystems, including the Serengeti ecosystem (Figure). Age information based on incisor tooth eruption was available for a subset of buffalo sampled in the Serengeti National Park and Ngorongoro Conservation Area during 2011–2012 (Table 1).

PPRV antibodies were detected by using the anti-hemagglutinin PPRV C-ELISA (Biological Diagnostic Supplies Limited [BDSL], Dreghorn, UK; www.bdsl2000.com/diagnostic-kits/ppr.aspx). Samples with positive results (i.e., inhibition value >50%) were confirmed as positive by using the anti-nucleoprotein PPRV C-ELISA (IDvet, Grabels, France; www.id-vet.com/produit/id-screen-ppr-competition/). The assays were performed and analyzed according to the manufacturers’ instructions.

The screening for PPRV antibodies in cattle showed that 26.7% of the samples from cattle that were alive during the 2008 PPR outbreak were seropositive, and 5.9% of those from cattle born after the outbreak were seropositive. Seroprevalence in village cattle ranged from 7% to 48% (Figure). No detailed clinical information was available for the period of the outbreak.

Except for 1 borderline positive buffalo sample (inhibition value 56.6%), no seropositive samples were detected among samples from 266 buffalo, 59 Thomson’s gazelles, and 6 Grant’s gazelles. The borderline seropositive buffalo was from the Arusha ecosystem and would have been alive during the 2008 PPR outbreak. PPR-seronegative buffalo included older animals (i.e., >4 years) from Serengeti National Park (n = 20) and Ngorongoro Conservation Area (n = 85) that were alive at the time of the 2008 outbreak and younger animals from Serengeti National Park (n = 10) and Ngorongoro Conservation Area (n = 35).

Our findings show higher rates of PPR seropositivity in cattle than found in previous studies and confirm that cattle are susceptible to PPR (1,2). These data support the view that in pastoral communities of northern Tanzania, where small ruminants and cattle co-exist, cross-species transmission of PPRV from small ruminants to cattle is likely to occur frequently.

Two broad conclusions can be drawn from these results. First, cattle are likely to be helpful indicators of PPRV circulation in mixed livestock communities and are therefore a useful population for surveillance. The study indicates that surveillance in cattle may also prove helpful in areas where PPR mass vaccination campaigns in sheep and goats have been implemented and would add value to existing syndromic surveillance networks. This conclusion is supported by the detection of seropositive young cattle (1–2 years of age) in more recent years at a time when no clinical cases were reported in small ruminants in the area. Although transmission of the live attenuated PPR vaccine strain in the field cannot be completely ruled out, there is currently no evidence for vaccine strain transmission either in the field or through experimental infection studies (14). Second, the high potential for cross-species transmission of PPRV from small ruminants to cattle in areas where these species live in close proximity suggests that monitoring such livestock communities would be useful for detecting any changes in the apparent pathogenicity of PPRV, including the possible emergence of PPR as a disease in cattle populations.

This preliminary study provided no evidence for PPR infection of wild ruminants within northern Tanzanian ecosystems. However, wildlife are known to be susceptible to PPR (3,12), and seropositive African buffalo and antelopes have been found in other locations (15). This study had limitations that prevent us from drawing definitive conclusions about infection patterns in African wildlife: sampling was largely carried out within wildlife-protected areas where there is limited opportunity for contact with sheep and goats, and only a small number of potential wildlife hosts were sampled. Seroprevalence data from other African buffalo populations (R. Kock, pers. comm.) suggest that larger sample sizes may be required from each host population to detect seropositivity and for our conclusions to be more representative. Thus, we recommend further studies to monitor wildlife infection in populations living in closer proximity to livestock.