Modelling the Transmission Dynamics of African Animal Trypanosomiasis; A Case Study of Shimba Hills, Kwale County, Kenya

Abstract

African Animal Trypanosomiasis (AAT) is caused by parasites of the species Trypanosoma vivax, Trypanosoma congolense, and Trypanosoma rhodesiense. Of 48 sub-Saharan African nations, 36 have endemic cases of AAT. The disease is prevalent in savannah and woodland areas. It poses a major threat to livestock production and health in agro-pastoralist communities, many of which are located along the boundaries of wildlife reserves. Most epidemiological studies on AAT around Shimba Hills National Reserve (SHNR) have focused on the vectors (tsetse fly) and the host (cattle). No studies have been done to show how efficiently a trypanosome can be transmitted from tsetse fly to cattle in a certain population. This study used data from previous studies collected from five villages, Kipambane, Msulwa A, Shimba Hills, Pengo, and Mlafyeni, located around SHNR. A conceptual model to represent all the interactions and feedback in the system was developed.It is assumed that transmission occurs between cattle and tsetse flies only. The ordinary differential equations were formulated representing all the interactions and transitions in the model. The parameters and variables of the model were estimated and a compartmental SIR-SI model framework was developed for a period of 120 days, then implemented in RStudio V4.1.1. The basic reproduction number (R0) was estimated from the next-generation matrix.The model revealed that the susceptible cattle sub-population and tsetse fly sub-population decreased with time, while on the other hand, the infectious cattle and tsetse fly sub-population increased with time. The recovered cattle population also increased over time.The basic reproduction number was obtained as the most dominant eigenvalue of the Next-Generation Matrix (𝑅0= 2.73) = Ro >1. From the data, the infection rates were high in the tsetse fly population 6.23% (74/1190) compared to the cattle sub-population 5.64% (29/514).From the data, the susceptible, infectious, and removed cattle populations were high in Kipambane village while the susceptible and infectious tsetse fly populations were high in the Shimba Hills region respectively. In conclusion, this study developed a compartmental model to simulate the trypanosome-vector-host transmission dynamics in areas neighboring the SHNR, Kwale County. It also estimated the basic reproduction number and documented the distribution of transmission risk around SHNR. The data indicated that villages close to the National Reserve have high infection rates compared to those far from the park. The estimated basic reproduction number revealed that if the right control measures are not implemented, AAT cannot be easily eliminated in areas around Shimba Hills National Reserve. Information about the distribution of the transmission risk around SHNR can be used to guide farmers on transmission risks given the transmission trend with time and also areas where they can graze and water their livestock. The public health officers and the veterinary officers can also use the same information to manage AAT in villages around SHNR. This study's findings, model predictions, and the estimated R0, indicated that more efforts and tailored management measures need to be put in place towards successful elimination of AAT in the Shimba Hills region