Monitoring an epidemic of Theileria-associated bovine anaemia(Ikeda) in cattle herds in New Zealand.

Monitoring an epidemic of an emerging vector-borne disease can be problematic; particularly in a countrywhere vector-borne disease has previously had minimal impact on livestock. This paper describes meth-ods of past and current surveillance of the Theileria-associated bovine anaemia (Ikeda; TABA) epidemicin New Zealand, and the resulting inferences made.Over the three year period of the TABA epidemic a portfolio of surveillance methods has been used:case reporting (with subsidised PCR testing), syndromic surveillance, sentinel surveillance, testing con-venience samples for herd infection, as well as specific active surveillance initiatives to understand the tick vector distribution. Surveillance data have shown that the number of affected cattle herds has con-tinued to increase over time with seasonal peaks in spring and autumn coinciding with peak activity ofnymph and adult ticks respectively. In spring 2014, the epidemic extended south into areas that werepreviously considered to be unsuitable for the tick vector. As a result a survey was initiated that showedthat ticks were present in areas outside of the known distribution.Testing pooled blood samples from cattle herds across New Zealand showed there still remained asignificant percentage of herds where only non-Ikeda type infections were present, indicating that theseherds were at risk of future TABA (Ikeda) outbreaks. For some regions there had been a noticeable increasein the percentage of herds infected, yet with only a small increase in the number of outbreaks comparedwith the previous year. Thus, outbreaks had either gone unobserved or had not been confirmed by testing.In these regions extensive low-input beef farming could explain the non-detection observed. There wasa close relationship between the number of syndromic reports of anaemia and the number of confirmed cases of TABA (Ikeda), (P < 0.01, adjusted R-squared = 0.74).Active monitoring of the epidemic for a three year period has provided valuable insight into seasonalnature of the disease and its continuing impact. Information from multiple surveillance sources canhelp build up an understanding of the epidemiology, even when data from each individual surveillance stream are limited. The TABA (Ikeda) epidemic in New Zealand represents a useful case study of longterm monitoring where disease is caused by an emerging pathogen.