An outbreak of equine infectious anaemia in Ireland during 2006: the modes of transmission and spread in the Kildare cluster.

The research discusses an outbreak of Equine Infectious Anemia (EIA) in Ireland in 2006, with a particular focus on its modes of transmission, evident in clusters of cases found in the counties of Meath and Kildare. The authors also conduct an epidemiological investigation in the Kildare cluster and provide findings based on their detailed evaluation of the case.

Methodology

• The researchers investigated the Kildare cluster, comprising 38 EIA cases, using established epidemiological methods like defining, verifying, and identifying cases, data analysis focusing on timing, space, and animal factors, hypothesis development, implementation of control measures, and efficient communication of findings.
• Both confirmed and unconfirmed cases were considered in the research, with the former involving horses that had serological and/or virological proof of EIA virus infection, and the latter involving horses with only clinical or epidemiological signs consistent with EIA infection.
• A case-control study was conducted to expose the risk factors associated with being a case. The information about the hospital, including physical infrastructure, work practices, and defined events, was gathered through multiple site visits, staff interviews, daily admission sheets, and treatment records.
• The researchers also performed a multifaceted analysis of the transmission of infection by evaluating hypotheses associated with iatrogenic transmission, close contact transmission, and vector-borne transmission.

Results

• Out of total cases, 22 confirmed EIA cases were related to the Kildare cluster, including 21 horses that were hospital residents in Co. Kildare.
• The case-control study included a total of 60 horses, comprising 16 cases and 42 controls. The final multivariable model indicated that being a case was associated with the number of nights spent in the same barn with either the second or third primary case.

Discussion

• The findings suggest the lack of any substantial evidence in support of iatrogenic transmission within the hospital setting.
• Vector-borne transmission was also considered, given the several factors favoring such a mode, including favorable weather conditions. However, secondary cases were observed only among horses hospitalized before a specific date, without any active programme of fly control before or after.
• It’s speculated that the third primary case could be the more plausible source of infection, possibly by aerosol. However, further research is recommended to clarify the manner of the disease’s transmission.

Assumptions

• The analysis also hinged on several key assumptions regarding the initial infection source and infection dynamics upon its introduction.
• The assumptions state that one or more of the primary cases served as the initial infection source for each of the secondary cases, the probable primary cases played no significant role in the disease outbreak, and all the secondary cases were each a second-generation infection.

Potential implications and Relevance

• The authors highlight that hospital-acquired infection was a critical feature of the EIA outbreak in Ireland in 2006, despite the absence of any strong evidence pointing towards more common modes of disease transmission, like iatrogenic and vector-borne methods.
• It emphasized the requirement for more focussed research, contemplating aerosol and vector-borne transmission within a barn environment, due to the inexhaustive and speculative nature of the existing findings.