FeLV RNA in the spleen, blood and bone marrow of 31 cats with cytopenias
BMC veterinary research · 2019
In plain language
The study included 31 cats with clinical signs associated with FeLV and low counts of at least one type of blood cell. A test called RT-qPCR detected the virus's genetic material in every cat, while the serum antigen test was positive in 24 of the 31. The spleen contained significantly more viral RNA than blood or bone marrow, although viral RNA was also detected in the marrow. These results do not show that the amount of virus in the marrow causes low blood cell counts, and the available abstract does not clarify whether it is related to their type or severity.
Scientific detail
This clinical study in cats, published in BMC Veterinary Research in 2019 (doi: 10.1186/s12917-019-2208-y), compared FeLV RNA load in the spleen, whole blood and bone marrow of 31 cats with FeLV-associated clinical signs and at least one hematologic cytopenia. Although the source is listed as open-access full text, only the abstract was available for this assessment; no limitations section was provided. The abstract does not describe a control group of FeLV-negative or non-cytopenic cats.
Viral RNA was significantly more abundant in the spleen than in whole blood and bone marrow, a finding classified as level C evidence. The abstract provides no test statistic, effect size or p-value. Bone marrow contained detectable FeLV RNA, although at a lower level than the spleen. This is compatible with marrow involvement in FeLV-associated cytopenias, but it is an inference and does not demonstrate that marrow viral load causes the cytopenias. Nor does it indicate that the marrow is free of virus or that marrow infection is clinically unimportant.
RT-qPCR detected FeLV RNA in all 31 cats, while the rapid serum p27 antigen test was positive in 24 of the 31; this finding is also classified as level C evidence. Within this cohort, RT-qPCR detected viral RNA in more cats than tested positive for antigen. The abstract does not specify which tissue yielded the positive RT-qPCR result in the seven antigen-negative cats. Without a control group, these results do not establish the diagnostic accuracy of the tests.
The abstract lists anemia, thrombocytopenia, neutropenia and pancytopenia, but presents no analysis of tissue viral load by cytopenia type or severity, or in relation to marrow pathology. This relationship therefore remains unresolved in the available information, although the full text may address it. The findings bear on tissue selection when assessing FeLV in cats with cytopenias, without establishing a causal relationship between marrow viral load and hematologic abnormalities.
What we know
In this cohort of 31 cats with FeLV-associated clinical signs and cytopenias, RT-qPCR detected viral RNA in every cat and the serum antigen test was positive in 24. The spleen contained significantly more viral RNA than whole blood or bone marrow. Viral RNA was also detected in the marrow. The comparative and detection findings are classified as level C evidence; marrow involvement in the cytopenias is an inference, not a demonstration of causality.
What we don't know
The available abstract does not establish whether FeLV RNA load in bone marrow, spleen or blood is related to cytopenia type or severity, or to marrow pathology; the full text may address these questions. It also does not specify which tissue tested positive by RT-qPCR in the seven antigen-negative cats, or provide the test statistic, effect size or p-value for the tissue comparison. It describes no control group and provides no limitations section. Neither the diagnostic accuracy of the tests nor a causal relationship between marrow viral load and cytopenias is established.
Evidence
EvidenceLevel C — Preliminary evidenceConfidence 90/100
Viral RNA was significantly more abundant in the spleen than in whole blood and bone marrow in these cats.
Excerpt verified in the source — verbatim, in the source's own language“We detected a significantly greater number of viral RNA in the spleen compared with the whole blood and bone marrow.”
Spleen had the highest FeLV RNA load among the three hemolymphatic tissues sampled. The abstract gives no test statistic, effect size or p-value. It does not show that bone marrow is free of virus or that bone marrow infection is clinically unimportant.
EvidenceLevel C — Preliminary evidenceConfidence 90/100
In 31 cats with FeLV-associated clinical signs and at least one hematologic cytopenia, FeLV RNA was detected by RT-qPCR in all cats, whereas 24 of 31 were positive for serum FeLV antigen.
Excerpt verified in the source — verbatim, in the source's own language“Viral RNA copy numbers were detected in all cats by RT-qPCR whereas 24 out of 31 cats were positive for the serum FeLV antigen.”
RT-qPCR detected viral RNA in more cats than the p27 antigen rapid test did in this cohort. The abstract does not say which tissue gave the positive RT-qPCR result in the 7 antigen-negative cats, and there is no control group, so diagnostic accuracy is not established.
InferenceConfidence 55/100
Bone marrow contained detectable FeLV RNA in cytopenic cats, but at a lower level than spleen. This is compatible with marrow involvement in FeLV-associated cytopenias but does not show that viral load in marrow causes the cytopenias.
The abstract states that RNA was measured in bone marrow and that spleen levels were higher. It does not analyze marrow viral load against cytopenia type, severity or marrow pathology, so any causal link is unsupported.
Open questionConfidence 60/100
It is unknown whether FeLV RNA load in bone marrow, spleen or blood relates to the specific type or severity of cytopenia (anemia, thrombocytopenia, neutropenia, pancytopenia).
The abstract lists the cytopenia categories but reports no tissue viral load analysis by category. The full text may address this.
Provenance
Source: Comparative measurement of FeLV load in hemolymphatic tissues of cats with hematologic cytopenias.
AVA