Highly pathogenic avian influenza (HPAI A[H5N1]) clade 2.3.4.4b has circulated globally since its emergence from the goose/Guangdong/96 lineage and has repeatedly spilled over from avian reservoirs into mammalian hosts. Recent years saw continued evolution and reassortment within clade 2.3.4.4b, producing genotypes that spread into North America, including genotype B3.13, which has been detected in wild birds, domestic poultry, dairy cattle, and sporadically in other mammals. Field detections in 2024 included H5N1 confirmation in alpacas on a premises with infected poultry. Those field findings, together with cattle and small ruminant detections and human cases linked to livestock exposure, prompted experimental studies to define susceptibility, pathogenesis, shedding, and tissue tropism in camelids.
The authors performed a controlled experimental infection in alpacas using an HPAI H5N1 clade 2.3.4.4b virus of genotype B3.13 — the same genotype identified in US field cases. Six alpacas were inoculated intranasally. The study monitored clinical signs, body temperature, and food intake; collected nasal swab samples to assess viral RNA and infectious virus shedding; and conducted tissue analyses including immunohistochemistry and RNA in situ hybridization at defined time points postinfection. Serologic responses were also assessed to determine whether animals mounted an antibody response after challenge. Specific laboratory protocols, sampling schedules, and assay details are provided in the source but are not reproduced in full in this summary.
Following intranasal inoculation with H5N1 genotype B3.13, the alpacas generally experienced mild illness. Observed clinical findings included a slight increase in body temperature and reduced food intake for up to 3 days postinfection. Nasal swab specimens tested positive for viral RNA, and infectious HPAI H5N1 virus was recovered from those samples, demonstrating productive upper respiratory infection and shedding.
Tissue-level investigations conducted at 4 days postinfection localized viral presence to the nasopharyngeal tonsil and nasal conchae. Both immunohistochemistry and RNA in situ hybridization detected virus in these upper respiratory sites; other tissues did not show comparable viral detection at that timepoint according to the reported findings. Animals developed serologic responses consistent with infection; the source reports seroconversion but does not provide expanded serologic kinetics or geometric titers in the abstract.
The experimental challenge confirms that alpacas can be infected with HPAI A(H5N1) clade 2.3.4.4b genotype B3.13 and can support productive viral replication in the upper respiratory tract with detectable shedding from the nasal cavity. The restricted tissue distribution observed at 4 days postinfection — limited to the nasopharyngeal tonsil and nasal conchae — suggests a predominantly upper respiratory tropism in this experimental setting and timepoint.
Clinical illness in the study animals was generally mild and transient, limited to short-lived fever and reduced appetite. These findings are consistent with field reports in which some alpacas showed mild respiratory signs, reproductive losses, and seroconversion; in the field outbreak, milk and fetal tissues also tested positive in some instances, but the experimental study focused on respiratory infection dynamics.
Because alpacas can be productively infected and shed infectious virus from the nasal cavity, camelids should be considered in surveillance frameworks where clade 2.3.4.4b viruses circulate. The experimental results support the plausibility of cross-species exposure on mixed-species premises, as documented in field events where alpacas shared pasture or water sources with infected poultry. Detection of virus in upper respiratory tissues and nasal shedding highlights the need for sampling strategies that include nasal swabs and for biosecurity measures to limit contact between avian reservoirs and susceptible mammalian livestock.
The source reports findings from a small, controlled experimental cohort (6 alpacas) and provides results at specific early timepoints (including 4 days postinfection for tissue analyses). The study documents susceptibility, shedding, and localized tissue detection in that context but does not present extended transmission experiments, prolonged longitudinal tissue surveys, or detailed serologic kinetics in the abstract. Field heterogeneity, pregnancy-associated outcomes observed in outbreaks, and broader epidemiologic consequences were not fully addressed within this experimental report.
This experimental infection study demonstrates that alpacas are susceptible to HPAI A(H5N1) clade 2.3.4.4b genotype B3.13, develop generally mild clinical disease in this setting, shed infectious virus from the nasal cavity, and have viral localization to the nasopharyngeal tonsil and nasal conchae at 4 days postinfection. These results underscore the importance of including camelids in surveillance and reinforcing biosecurity on mixed-species farms in regions with active circulation of clade 2.3.4.4b H5N1 viruses.