FHV-1 antibodies and FeLV status in domestic cats in Namibia
Veterinary research communications · 2026
In plain language
A study of 236 cats in Namibia examined antibodies against feline herpesvirus type 1 (FHV-1) and their relationship with vaccination and FeLV status. It found no statistically significant association between detection of these antibodies and a positive or negative FeLV antigen test, but this does not show that the two groups have the same immune response. Some vaccinated cats without detectable antibodies were FeLV antigen-positive; this exploratory observation does not show that FeLV caused the finding or that vaccination had failed. The study cannot tell us whether these cats lacked immune protection.
Scientific detail
The observational clinical study published in Veterinary research communications in 2026 included 236 domestic cats from 15 towns in eight regions of Namibia. There were 23 vaccinated and 213 unvaccinated cats; 95 were FeLV antigen-positive and 141 antigen-negative; 10 were FIV antibody-positive and 226 antibody-negative. FHV-1 neutralising antibody detection was compared by FeLV antigen status. FHV-1 seropositivity was not significantly associated with that status in this cohort (OR = 0.40; 95% CI: 0.13–1.25). This preliminary observational evidence, rated level C, does not establish equivalence between the groups or exclude an effect on humoral immunity.
Some vaccinated cats without detectable FHV-1 neutralising antibodies were FeLV antigen-positive. The observation was explicitly described as exploratory, and the passage reporting it does not quantify this subgroup. It does not demonstrate that FeLV caused the absence of detectable antibodies, that protective immunity was absent, or that vaccination had failed. Whether FeLV-related impairment of humoral immunity explains this finding remains an open question. The study cannot distinguish that possible mechanism from differences in vaccination history, waning antibodies, or assay limitations. The authors call for larger, targeted cohorts to investigate this observation.
Only 18 cats were FHV-1 seropositive and only 23 had a recorded vaccination history, limiting subgroup analyses and precluding adequately powered multivariable regression. Neither multivariable regression nor adjustment for multiple comparisons was performed. These limitations constrain assessment of confounding and the strength of conclusions about vaccination and retroviral status. Convenience sampling limits population representativeness; regional sample sizes were uneven and sometimes very small. Vaccine formulation, timing, booster status, and handling conditions were unavailable. Individual feeding mode and indoor/outdoor environment were not recorded either.
FeLV antigen status was not independently re-tested, so misclassification based on previously reported antigen testing could not be excluded; this does not demonstrate that any particular cat was misclassified. Cellular immune responses were not evaluated. Antibody detection does not establish active FHV-1 infection, and seronegativity does not exclude previous infection. Laboratory assay controls do not make this an experimentally controlled study of feline immunosuppression: it does not establish FeLV-induced suppression of FHV-1 antibody responses, altered cellular immunity, or vaccine failure.
What we know
Preliminary observational evidence, rated level C, showed no statistically significant association between FHV-1 seropositivity and FeLV antigen status in this cohort (OR = 0.40; 95% CI: 0.13–1.25). Some vaccinated cats without detectable neutralising antibodies were FeLV antigen-positive, an exploratory observation whose subgroup is not quantified in the relevant passage. The small numbers of seropositive cats and cats with recorded vaccination histories, together with sampling, analytical, and FeLV classification limitations, constrain the conclusions.
What we don't know
Whether FeLV-related impairment of humoral immunity explains absent detectable FHV-1 neutralising antibodies in some vaccinated FeLV-positive cats is unknown. Possible FeLV effects have not been separated from differences in vaccination history, waning antibodies, or assay limitations. The study does not determine whether these cats lacked protective immunity or demonstrate vaccine failure. It also does not assess cellular immunity, establish equivalence between the FeLV groups, or rule out errors in FeLV antigen classification. The presence of antibodies does not establish active FHV-1 infection, and their absence does not exclude previous infection.
Evidence
EvidenceLevel C — Preliminary evidenceConfidence 100/100
The study's subgroup analyses were limited by only 18 seropositive cats and 23 cats with a recorded vaccination history; multivariable regression and multiple-comparison adjustment were not performed.
Excerpt verified in the source — verbatim, in the source's own language“Multivariable logistic regression was not considered sufficiently powered and no adjustment for multiple comparisons was applied, because only 18 cats were seropositive and only 23 cats had a recorded vaccination history.”
These limitations constrain assessment of confounding and the strength of subgroup conclusions, including those concerning vaccination and retroviral status. Laboratory assay controls do not make this an experimentally controlled feline immunosuppression study.
EvidenceLevel C — Preliminary evidenceConfidence 100/100
Some vaccinated cats without detectable FHV-1 neutralising antibodies were FeLV antigen-positive, an observation explicitly described as exploratory.
Excerpt verified in the source — verbatim, in the source's own language“An exploratory observation in the present study was that a proportion of vaccinated cats lacking detectable neutralising antibodies were FeLV antigen-positive.”
The passage does not quantify this subgroup or establish that FeLV caused the absence of detectable antibodies. It does not demonstrate absence of protective immunity or vaccine failure.
EvidenceLevel C — Preliminary evidenceConfidence 100/100
The study did not independently re-test FeLV status, and the authors could not exclude misclassification from previously reported antigen testing.
Excerpt verified in the source — verbatim, in the source's own language“Since FeLV status was derived from previously reported antigen testing (De Villiers et al. 2025 ) and not independently re-tested in the present analysis, possible misclassification cannot be fully excluded.”
Uncertainty in the FeLV classification limits interpretation of the retroviral association analysis; this does not demonstrate that any particular cat was misclassified.
EvidenceLevel C — Preliminary evidenceConfidence 100/100
FHV-1 seropositivity was not significantly associated with FeLV antigen status in this cohort (OR = 0.40; 95% CI: 0.13–1.25).
Excerpt verified in the source — verbatim, in the source's own language“Likewise, no associations were detected between seropositivity and FIV antibody positivity (OR = 1.37; 95% CI: 0.16–11.43) or FeLV antigen status (OR = 0.40; 95% CI: 0.13–1.25) (Table 3 ).”
This is a preliminary observational association analysis, not an experimental test of FeLV-mediated immunosuppression. The result does not establish equivalence between FeLV-positive and FeLV-negative cats or exclude an effect on humoral immunity.
Open questionConfidence 99/100
Whether FeLV-related impairment of humoral immunity explains absent detectable FHV-1 neutralising antibodies in vaccinated FeLV-positive cats remains an open question.
The authors call for larger targeted cohorts to investigate this observation. The current study does not resolve the mechanism or separate FeLV-related effects from vaccination-history differences, waning antibodies, or assay limitations.
Provenance
Source: Tracing feline herpesvirus-1 exposure in domestic cats from Namibia: associations with neutralising antibodies, vaccination, clinical signs, and retroviral status.
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