Understanding the legal trade of cattle and camels and the derived risk of Rift Valley Fever introduction into and transmission within Egypt

Abstract

Rift Valley Fever (RVF) is a mosquito-borne zoonosis, which may cause significant losses for the livestock sector and have serious public health implications. Egypt has been repeatedly affected by RVF epidemics, mainly associated to the importation of animals from sub-Saharan countries, where the disease is endemic. The objective of our study was the improvement of the surveillance and control strategies implemented in Egypt. In order to do that, first we evaluated the legal trade of live animals into and within Egypt. Then, we assessed the risk of Rift Valley Fever virus (RVFV) transmission within the country using a multi-criteria evaluation approach. Finally, we combined the animal trade and the risk of RVFV transmission data to identify those areas and periods in which the introduction of RVFV is more likely. Our results indicate that the main risk of RVFV introduction is posed by the continuous flow of large number of camels coming from Sudan. The risk of RVFV transmission by vectors is restricted to the areas surrounding the Nile river, and does not vary significantly throughout the year. Imported camels are taken to quarantines, where the risk of RVFV transmission by vectors is generally low. Then, they are taken to animal markets or slaughterhouses, many located in populated areas, where the risk of RVFV transmission to animals or humans is much higher. The measures currently implemented (quarantines, vaccination or testing) seem to have a limited effect in reducing the risk of RVFV introduction, and therefore other (risk-based) surveillance strategies are proposed.

Fig 1. Distribution by species (density of animals, vaccine coverage and density of susceptibles).

Upper row: density of cattle, sheep, goat and buffaloes (animals per square kilometer). Middle row: vaccine coverage for cattle, sheep, goat and buffaloes. Lower row: density of susceptible cattle, sheep, goat and buffaloes (animals per square kilometer).

Fig 2. Importation of camels and cattle.

Monthly importation into Egypt of camels and cattle between 2012 and 2015. In red animals imported from Sudan, and in blue animals imported from Ethiopia.

Fig 3. Legal trade routes for cattle and camels imported into Egypt from Sudan and Ethiopia.

Fig 4

Location of the 273 animal markets by connectivity (A) and by RVFV susceptible species traded (B).

Fig 5. Location of the 51 animal markets with the highest risk for RVFV transmission (risk score above 10).

Fig 6

Location of the slaughterhouses by number of animals slaughtered for camels (A) and for cattle (B).

Fig 7

Standardized distribution of susceptible hosts of RVFV (A), and standardized distribution of of competent vectors of RVFV (B).

Fig 8. Standardized map of the risk of RVFV transmission by vectors in Egypt.

Circles indicate the areas at the highest risk: Cairo area and to its north (1), Faiyum, Beni Suef and Minya area (2), Asyut, Sohag and Qena area (3), and Luxor area (4).

Fig 9. Risk of RVFV transmission by vectors at the locations of previous outbreaks and at the main animal markets.

(A) Risk of RVFV transmission by vectors at the locations where outbreaks from previous epidemics occurred. (B) Risk of RVFV transmission by vectors at the locations where the 51 main animal markets are located. Large blue circles represent the two markets with the highest risk (Birqash market in Giza governorate and Daraw market in Aswan).

Fig 10. Risk of RVFV transmission by vectors at the locations of quarantines and camel slaughterhouses.

Risk of RVFV transmission by vectors at the locations where quarantines are located (A). Risk of RVFV transmission by vectors at the locations where the camel slaughterhouses are located (B). Large blue circles represent the three slaughterhouses that kill the most camels.