Vulture declines and increased dog scavenging

Ogada, D. L., Torchin, M. E., Kinnaird, M. F., & Ezenwa, V. O. (2012). Effects of vulture declines on facultative scavengers and potential implications for mammalian disease transmission. Conservation Biology, 26(3), 453-460.

Vultures (Accipitridae and Cathartidae) are the only known obligate scavengers. They feed on rotting carcasses and are the most threatened avian functional group in the world. Possible effects of vulture declines include longer persistence of carcasses and increasing abundance of and contact between facultative scavengers at these carcasses. These changes could increase rates of transmission of infectious diseases, with carcasses serving as hubs of infection. To evaluate these possibilities, we conducted a series of observations and experimental tests of the effects of vulture extirpation on decomposition rates of livestock carcasses and mammalian scavengers in Kenya. We examined whether the absence of vultures changed carcass decomposition time, number of mammalian scavengers visiting carcasses, time spent by mammals at carcasses, and potential for disease transmission at carcasses (measured by changes in intraspecific contact rates). In the absence of vultures, mean carcass decomposition rates nearly tripled. Furthermore, the mean number of mammals at carcasses increased 3-fold (from 1.5 to 4.4 individuals/carcass), and the average time spent by mammals at carcasses increased almost 3-fold (from 55 min to 143 min). There was a nearly 3-fold increase in the mean number of contacts between mammalian scavengers at carcasses without vultures. These results highlight the role of vultures in carcass decomposition and level of contact among mammalian scavengers. In combination, our findings lead us to hypothesize that changes in vulture abundance may affect patterns of disease transmission among mammalian carnivores.

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Los buitres (Accipitridae y Cathartidae) son los únicos carroñeros obligados que se conocen. Se alimentan de cadáveres en descomposición y son el grupo funcional de aves más amenazado del mundo. Los efectos posibles de las declinaciones de buitres incluyen una mayor persistencia de cadáveres y el incremento de la abundancia de y contacto entre carroñeros facultativos en esos cadáveres. Estos cambios podrían incrementar las tasas de transmisión de enfermedades infecciosas, con los cadáveres funcionando como focos de infección. Para evaluar estas posibilidades, realizamos una serie de observaciones y pruebas experimentales de los efectos de la extirpación de buitres sobre las tasas de descomposición de cadáveres de ganado y mamíferos carroñeros en Kenia. Examinamos sí la ausencia de buitres cambiaba el tiempo de descomposición de cadáveres, el número de mamíferos carroñeros visitando los cadáveres, el tiempo utilizado por mamíferos en los cadáveres y la potencial transmisión de enfermedades en los cadáveres (medida por cambios en las tasas de contacto interespecífico). En ausencia de buitres, las tasas medias de descomposición de cadáveres incrementaron 3 veces (de 1.5 a 4.4 individuos/cadáver), y el tiempo promedio invertido por mamíferos en los cadáveres incrementó casi 3 veces (de 55 min a 143 min). Hubo un aumento de casi tres veces en el número promedio de contactos entre mamíferos carroñeros en cadáveres sin buitres. Estos resultados resaltan el papel de los buitres en la descomposición de cadáveres y del nivel de contacto entre mamíferos carroñeros. En combinación, nuestros resultados nos llevaron a plantear la hipótesis de que cambios en la abundancia de buitre pueden afectar los patrones de transmisión de enfermedades entre mamíferos carnívoros.

A CDV epidemic in Serengeti

Roelke-Parker, M. E., Munson, L., Packer, C., Kock, R., Cleaveland, S., Carpenter, M., ... & Mwamengele, G. L. (1996). A canine distemper virus epidemic in Serengeti lions (Panthera leo). Nature, 379(6564), 441-445.

CANINE distemper virus (CDV) is thought to have caused several fatal epidemics in canids within the Serengeti–Mara ecosystem of East Africa, affecting silver-backed jackals (Canis mesomelas) and bat-eared foxes (Otocyon megalotis) in 1978 (ref. 1), and African wild dogs (Lycaon pictus) in 1991 (refs 2, 3). The large, closely monitored Serengeti lion population4,5 was not affected in these epidemics. However, an epidemic caused by a morbillivirus closely related to CDV emerged abruptly in the lion population of the Serengeti National Park, Tanzania, in early 1994, resulting in fatal neurological disease characterized by grand mal seizures and myoclonus; the lions that died had encephalitis and pneumonia. Here we report the identification of CDV from these lions, and the close phylogenetic relationship between CDV isolates from lions and domestic dogs. By August 1994, 85% of the Serengeti lion population had anti-CDV antibodies, and the epidemic spread north to lions in the Maasai Mara National reserve, Kenya, and uncounted hyaenas, bat-eared foxes, and leopards were also affected.

Dog ecology and demography in Machakos District, Kenya

Kitala, P., McDermott, J., Kyule, M., Gathuma, J., Perry, B., & Wandeler, A. (2001). Dog ecology and demography information to support the planning of rabies control in Machakos District, Kenya. Acta Tropica, 78(3), 217-230.

A study of 150 dog-owning households from six randomly selected sublocations was conducted in Machakos District, Kenya. Initially, all households were visited to collect information on dog ecology and demography based on WHO guidelines and to collect serum for rabies antibody detection. A second visit was made 1 year later, to obtain follow-up data on births, deaths, dog movements and other events since the first visit. Dog ownership was common, with a range of 53–81% (mean=63%) of households owning dogs in the six sublocations. Dog density for the five more rural sublocations ranged from 6 to 21 dogs  km^-2 and for the peri-urban sublocation was 110 dogs  km^-2. The dog population was estimated to be growing at 9% p.a. (95% C.I. 4–14%). This growth was a function of very high fecundity (1.3 females per female per year) more than compensating for high mortality, particularly among females. Life expectancy from birth was 3.5 years for males and 2.4 years for females. Half the dogs at any one time were less than 1 year of age. All dogs, by design of the study, were owned. Of these, 69% were never restricted and roamed freely to forage for food and mix with other dogs. Only a small proportion of dogs (5%) were fed commercial dog food. Most households reported observing dogs scavenging their garbage, including: their own dogs (81%), their neighbours’ dogs (75%) and unknown dogs (45%). Only 29% of dogs at least 3 months of age were reported to be vaccinated against rabies. The proportion vaccinated varied widely between sublocations (5–68%); 48% of dogs reportedly vaccinated had detectable antibodies, 31% at or above levels considered to indicate seroconversion. The proportion of dogs with detectable antibodies declined according to the time since last vaccination (55% if vaccinated ≤1 year, 47% ≤2 years and 36% >2 years); 20% of dogs reported not to have been vaccinated had detectable rabies antibody. Compared to other dog populations in rural eastern and southern Africa, Machakos District has a high density of dogs. The Machakos dog population is growing, highly dynamic, poorly supervised and inadequately vaccinated against rabies. The main implication for rabies control is that adequate vaccination coverage is unlikely to be achieved, even under optimal delivery, using the current strategy of annual vaccination of dogs older than 3 months.

Canine distemper impact on African wild dogs

Alexander, K.A. & M.J. Appel. 1994. African wild dogs (Lycaon pictus) endangered by a canine distemper epizootic among domestic dogs near the Masai Mara National Reserve, Kenya. Journal of Wildlife Diseases, 30 (4): 481-485

A longitudinal study of canine distemper (CD) among domestic dogs on Malsai communal land to the north of the Masai Mara National Reserve in Kenya was conducted from 1989 to 1991. Prevalence of antibodies to CD was very low among domestic dogs in 1989 and 1990 (4%, n = 49; and 1%, n = 119, respectively) and no African wild dogs (Lycaon pictus; n = 16) collected simultaneously from the same area had detectable antibodies. Among 51 domestic dogs sampled in 1991, however, prevalence of CD antibodies rose significantly (P < 0.01) to 76%. Disease-related mortality rates among domestic dogs were estimated from 1990 to 1992; they rose significantly (P < 0.01) from 21% in 1990 to 50% in 1991 and then decreased significantly (P < 0.01) to 38% in 1992. The 1992 mortality rate remained significantly (P < 0.01) higher than that of 1990. Signs observed in clinically ill domestic dogs were consistent with CD and included listlessness, decreased appetite, bilateral serous to mucopurulent oculonasal discharge, and diarrhea. No carcasses could be retrieved for virus isolation and postmortem examination. Concurrent with this CD epizootic in domestic dogs, the known African wild dog packs in this region disappeared.