Key Findings
By combining sight-resight and household surveys, researchers discovered significant variability in the human-to-dog ratio (HDR) across different communities in Guatemala.
Relying on the standard 5:1 HDR is likely to underestimate dog populations in rural and semi-urban areas, potentially hindering efforts to achieve 70% vaccination coverage and eliminate rabies.
Researchers found that dog density was more closely correlated with human population density than with the total human population, suggesting it could be a viable alternative for estimating dog populations when direct surveys are not feasible.
Summary
Accurate dog population estimates are crucial for effective rabies vaccination campaigns. However, many countries face difficulties in conducting these estimates. The human-to-dog ratio (HDR) is often used to estimate dog populations, but it can vary widely between communities. This makes it unreliable for predicting dog populations in different areas. In Latin America, HDRs range from 4.6 to 7.6, making vaccination planning challenging.
Guatemala’s Ministry of Health has used a 5:1 HDR for vaccination planning since 2010. However, this ratio is based on data from neighboring countries and hasn’t been verified in Guatemala. Previous studies suggest that HDRs vary across different regions in the country, but their findings are limited in scope.
Despite reported vaccination rates exceeding 70%, rabies persists in certain Guatemalan communities. This may be due, in part, to inaccurate dog population estimates. To address this, the researchers investigated the variability of human-to-dog ratios (HDRs) across different regions in Guatemala by employing various estimation methods.
Study Methods
The study, titled “Heterogeneity in Dog Population Characteristics Contributes to Chronic Under-Vaccination Against Rabies in Guatemala,” compared different methods (sight-resight surveys, household surveys, or a combination) to estimate dog populations in 16 high-risk Guatemalan communities.
The research was carried out across eight health areas in Guatemala, covering 16 communities that included urban (5), semi-urban (3), and rural (8) settings. These communities were identified as high-risk for rabies due to either (i) the presence of at least one rabid dog within the past three years, or (ii) at least one case of dog-mediated human rabies in the last 15 years.
Sight-Resight Surveys (SRS)
SRS involved teams walking designated transects, recording characteristics of all dogs sighted. This process was repeated the next day to identify previously seen dogs. The total number of free-roaming dogs was estimated by extrapolating the human population of each transect to the total population in each community.
Household Surveys (HHS)
HHS surveyed selected households in the community on owned dogs, household size, and dogs allowed to roam freely. Data helped classify dogs into three categories: always confined, semi-confined, and never confined. Surveys also inquired about feeding community dogs. The total number of owned dogs was estimated by extrapolating the number of dogs per household using the sampling fraction of surveyed households. In cases where HHS and SRS methods were used together, the surveyed households were located along the same transects as the dog counts.
Combined Population Analysis
Researchers conducted a combined population analysis to determine overall dog population demographics in areas where both SRS and HHS were used. The total dog population was calculated as the sum of owned confined dogs, owned semi-confined dogs, owned never-confined dogs, and community dogs.
Survey Results
The study conducted 919 HHS and walked 119 kilometers for SRS in 16 communities. Rural communities had an adjusted human-to-dog ratio (aHDR) of 3.0 (range of 1.7 to 4.9). Semi-urban communities had an aHDR of 2.8 (range of 1.7 to 3.9), while urban communities had the highest aHDR, with a value of 6.3 (range of 2.7 to 11.4).
There was a large degree of heterogeneity in the communities, with the researchers’ estimate resulting in significantly lower aHDRs (and therefore higher estimated dog populations) than the national estimate in 10 of the 16 communities assessed. Overall, these 10 communities had dog populations that were 1.6-fold higher than official estimates. This would equate to a 60% decrease in the estimated vaccination coverage. On the other hand, in two urban areas the aHDR was higher than the official estimate, meaning the dog populations are overestimated in those places.
The researchers also found that:
- Owned confined dogs were more common in urban and semi-urban areas (23% and 37%, respectively) compared to rural areas (14%).
- Owned free-roaming dogs were most prevalent in rural areas (73%), followed by semi-urban (48%) and urban (71%) areas.
- Community dogs were relatively similar across all areas, with rural areas having slightly more (13%) than urban (7%) and semi-urban (15%).
Improving Dog Population Estimation Strategy
Using only household surveys or sight-resight surveys can undercount dogs. Household surveys miss free-roaming dogs, while sight-resight surveys can’t tell if dogs are owned or not. This is especially a problem in areas with many community or owned-confined dogs. Combining both methods is often needed, except in communities where one of these groups is mostly absent.
In the study, all communities had many owned dogs that stayed at home, so household surveys were needed. Community dogs were only counted in six places where both surveys were used, and they were found in four of these. This shows that sight-resight surveys are also important in most places to get a complete picture of the dog population. But combining both methods costs more.
The study found that the national 5:1 ratio often underestimates the number of dogs in most communities, except in cities. It also showed that there’s a connection between the number of dogs and how many people live in a certain area. This means we can estimate dog populations more accurately based on human population density, even without doing surveys. This is helpful when there aren’t enough resources for field studies. Additionally, the study found that focusing on areas with persistent rabies cases is better for controlling rabies than trying to count every dog in the whole country.
Miscellaneous
Data From Study:
–
Year of Publication:
2022
External Link:
Moran D, Alvarez D, Cadena L, Cleaton J, Salyer SJ, Pieracci EG, et al. (2022) Heterogeneity in dog population characteristics contributes to chronic under-vaccination against rabies in Guatemala. PLoS Negl Trop Dis 16(7): e0010522.
https://doi.org/10.1371/journal.pntd.0010522