The Influence of Demographic, Spatial and Behavioural Heterogeneities on Urban Domestic Dog Populations on Rabies Transmission and Control in Iringa, Tanzania

Alena Gsell (MSc Study at the Swiss Tropical Institute, Basel)

Rabies is a fatal but preventable zoonosis which infects all mammals. Transmission of the virus is mediated through close contact of injured skin with saliva or high density aerosols of infected individuals. In developing countries, rabies is maintained predominantly among domestic dogs that therefore play the most important role in the transmission of the virus to humans. Rabies is endemic in most African countries and the incidence of dog and human rabies is increasing despite commercial availability of effective post exposure treatment and dog rabies vaccines. In Tanzania where rabies has reoccurred again since 1977, domestic dogs are the main reservoir of rabies. 90% of human rabies deaths result of dog bites. Children below 15 years are affected most often. It has been shown that the prevalence of rabies in domestic dogs can be lowered significantly by vaccination campaigns and thus also does reduce the risk of infection for the human population as well as the costs that arise from the expensive and time consuming post exposure treatment against rabies.
Yet, most studies on rabies dynamics have focused on wildlife carriers in Europe and North America where dogs are not the primary reservoir and rabies in humans is rare. However, successful European vaccination strategies can not be transferred without adaptation to African settings due to lack of money, infrastructure and logistics and especially due to differing reservoir species. Out of the few rabies studies that have looked at dog ecology and rabies control measures in Africa, most have focused on rural settings, leaving open a need for more information on urban dog ecology and rabies control measures.
In order to gain an insight into the factors ruling the rate and dynamics of rabies transmission and to decide on the most appropriate control strategy, the study collected baseline-data on dog life history, accessibility to vaccination, spatial distribution and territory size, contact behaviour and on dog management, handling habits and dog bite numbers in four studywards in Iringa, a middle sized town in the Southern highlands of Tanzania. Total dog numbers and distribution of dogs were collected during a full census in 7994 households. Data on dog demography and the owner’s perception of dogs were collected by means of 350 questionnaires. 29 dogs were collared with a GPS equipped collar to determine the size of an average homerange. The number of dogs accessible to vaccination was assessed during a vaccination campaign and all accessible dogs were marked. By means of transects, the proportion of feral dogs roaming in the streets were to be estimated. A survey on dogbite-victims who presented for medical care, and a traceback study on recipients of post exposure treatment as well as on the dogs responsible for the bite were conducted. And lastly, a behavioural study examined the range of contact types among dogs and between dogs and humans or livestock.
The aim of the study was to pull together data on urban dog population biology, accessibility and movement patterns in order to answer two questions. Firstly, is there a specific subpopulation of the overall dog population that is likely to be missed in vaccination campaigns and is the same subpopulation predominantly accountable for most of the bite cases. And secondly, risk of contracting rabies may not be evenly distributed in the population. Thus, are there any differences in contact patterns, spatial distribution, restriction and accessibility that render a certain subpopulation more likely to contract or spread rabies. Piloting the methods and training of staff was done in Arumeru, Arusha, and the actual fieldwork was conducted in Iringa, Tanzania, from April to December 2005, the analysis of the data is still going on.

Collaborations
The study would not have been possible without the dedication of the Tanzanian team and was conducted in joint collaboration with

• PD Dr. Jakob Zinsstag, Human and Animal Health Group (HAH), Swiss Tropical Institute, Basel, Switzerland,
  
• Prof. Rudovick Kazwala, Veterinary Faculty, Sokoine University of Agriculture, Morogoro, Tanzania and
  
• Dr. Sarah Cleaveland and Dr. Darryn Knobel, Centre for Tropical Veterinary Medicine (CTVM), Edinburgh,    
    United Kingdom,

and is embedded in a greater study on improving cost-effectiveness of rabies control in Tanzania which is run by the CTVM. The study also strengthened and broadened the well established collaboration between the HAH and the Sokoine University on bovine tuberculosis and complemented the ongoing HAH rabies research “Towards a Rabies-Free N’Djaména” in Chad.

Towards the evening of the first day of the vaccination campaign, all attendants and their dogs look for shade
or tiredly set out for their return homeward.