DIAGNOSIS
Diagnosis of herpesvirus infections in a clinical setting is largely based on clinical presentation, potentially coupled with a history of recent stress or comorbidity. Infections may be confirmed by demonstration of characteristic histopathological changes, which often include inflammation, widespread congestion and necrosis, and the identification of intranuclear inclusion bodies, often in the liver, spleen, lymph nodes and the respiratory and genitourinary tracts (Finnie et al.
1976; Dickson et al. 1980; Wilks et al. 1981; Rothwell et al. 1988; Besier et al. 2016). Herpesvirus virions may be definitively identified by electron microscopy of tissue samples or viral isolates (Fig. 23.2). PCR is useful in ante-mortem diagnosis and molecular classification of confirmed cases. The collection of swabs from the conjunctivae, oropharynx and cloaca for PCR testing should be performed in suspected cases (Stalder et al. 2015).A point of care isothermal assay and a rapid qPCR have recently been developed and validated for the detection of PhaHV-1 in koalas, hoped to assist in furthering research into the prevalence and significance of this gammaherpesvirus across endangered koala populations in NSW, ACT and Qld (Wright et al. 2023).
Serum-virus neutralisation testing is a useful screening tool for managed macropod populations to identify individuals previously exposed to MaHV-1, -2 and -4 and immunologically naive animals that may be susceptible to more severe disease if infected. It is not an effective modality for differentiating between lytic or latent infection and thus cannot determine whether herpesvirus infection is responsible for the pathology identified clinically.
Fig. 23.2. Transmission electron micrograph showing macropodid herpesvirus 2 propagated in wallaby fibroblast cell culture. The virion (arrow) comprises a spherical capsid surrounded by an irregularly-shaped envelope, giving a characteristic 'fried egg' appearance. Non-enveloped capsids are also present, as well as cells and cellular debris. Bar = 100 nm. Electron micrograph: Paola Vaz and Liliana Tatarczuch
5.