This research article published by Elsevier B.V., 2019
Infection and Treatment Method (ITM) has been practiced in Tanzania for over 20 years as a
prevention measure against East Coast Fever disease. It is known that ITM, like natural ECF
infection, leads to a carrier state, whereby vaccinated cattle become asymptomatic carriers of the
parasite. It is expected that ECF vaccination using ITM also leads to generation of combinations
of vaccine specific Theileria parva and local strains that circulate in the field what contributes to
an unknown level of parasite diversity. Moreover, the long term impact of ITM on carrier state
and parasite diversity in cattle are largely unknown. To address this question blood was collected
from ECF-vaccinated (n = 239) and unvaccinated (n = 97) cattle from Loiborsoit, Emboreet,
Esilalei, Manyara ranch and Mswakini villages in the Maasai steppe of northern Tanzania, as well
as Mruazi and Leila farms in Tanga in eastern Tanzania. Screening for T. parva using nested PCR
revealed an overall prevalence of T. parva to be 34.5%, with a significant higher prevalence among
ECF-vaccinated cattle. Using three VNTR markers (ms2, ms5 and MS7) higher parasite genetic
diversity in terms of higher number of alleles and expected heterozygosity was shown in
vaccinated than unvaccinated cattle. These parameters were highest in cattle from Manyara ranch.
Nevertheless, the principle component analysis (PCoA) showed no distinct clustering patterns as
most T. parva alleles clustered together throughout the four quadrants implying parasite
homogeneity among the sampled populations. However, some of the parasite alleles closely
clustered with Muguga vaccine alleles in two of the quadrants, consistent with closer genetic
relatedness between the vaccine strains and the T. parva populations from the Maasai steppe.
Likewise analysis of molecular variance (AMOVA) revealed most of the genetic variation (93%)
being contained within populations with only 7% being among populations. This study therefore
confirms the role of ECF vaccination in enhancing carrier state and T. parva diversity in vaccinated
cattle populations. Higher T. parva diversity may play an important role in carrier cattle by way of
restricting breakthrough infections from field parasite strains.