Fatal West Nile Virus Infection Research Articles

Fatal West Nile Virus Infection in Horse Returning to United Kingdom from Spain, 2022.

We report fatal West Nile virus (WNV) infection in a 7-year-old mare returning to the United Kingdom from Spain. Case timeline and clustering of virus sequence with recent WNV isolates suggest that transmission occurred in Andalusía, Spain. Our findings highlight the importance of vaccination for horses traveling to WNV-endemic regions.

Reply to Keynan et al

To the Editor—We appreciate the concerns regarding CCR5 blockade expressed by Keynan et al. While animal models may provide a rationale to proceed to human studies, they may not always predict the observations or results that human studies yield. We acknowledge the reports of symptomatic West Nile infection in persons with a Δ32 mutation of the CCR5 receptor. Although these reports are scientifically intriguing, well-controlled prospective studies would be needed to determine the association of risk of severe or fatal West Nile virus infection in persons with the Δ32 mutation. A similar argument can be made regarding the risks of vaccination with yellow fever virus vaccine or the risk of tickborne encephalitis virus that have been reported. As for a broader risk for severe flavivirus infection among persons with the Δ32 mutation, this remains a hypothetical concern. Pharmacologic blockade of the CCR5 receptor may not behave in the same manner as a genetic polymorphism in the CCR5 receptor of all cells, which could modulate the clinical outcome of the infection. These questions emphasize the need for continued follow-up of patients treated with CCR5 antagonists. Vicriviroc has been studied in over 1600 subjects, some of whom have been treated for up to 4 years. We have not observed an excess of morbidity or mortality due to severe infections or unexplained complications that would suggest an untoward risk for those receiving vicriviroc. We continue to follow up patients receiving vicriviroc on long-term extension studies and continue evaluation of the risks expressed by the authors.

Targeting the Chemokine Receptor CCR5: Good for HIV, What about Other Viruses?

To the Editor—We read with interest the report by Suleiman et al [1] on the encouraging results of the VICTOR-E1 Phase 2 Trial, demonstrating vicriviroc's good and sustained antiretroviral and immunologic activity over 48 weeks in treatment-experienced HIV-infected individuals. These promising results need to be balanced with caution against the possibility that treatment could lead to more severe manifestations of other viral infections; this is due to the mechanism of action of vicriviroc and the significant role of CCR5 in the response to viral infections other than HIV. CCR5 is a chemokine receptor expressed on a variety of immune cells and is responsible for mediating leukocyte chemotaxis and homing to sites of infection. Until recently, understanding of the role of CCR5 was limited to its role in HIV cell entry and the protection from HIV afforded by its absence. More recent evidence is mounting to link CCR5 receptor deficiency (ie, the presence of the CCR5Δ32 allele) with an increased risk of symptomatic and fatal West Nile virus infection [2–4]. Additionally, a severe adverse reaction to the yellow fever virus vaccine in a CCR5Δ32 heterozygote and an association of the Δ32 mutation with severe tickborne encephalitis symptoms [5, 6] suggest a broader role for CCR5 in flaviviral infections. Several lines of evidence point to the CCR5Δ32 allele being important in determining disease severity of other viral infections, albeit in animal models. In a mouse model, challenge of CCR5-deficient animals with influenza virus was associated with impaired recruitment of CD8+ to the lungs, accompanied by an increased mortality rate [7, 8]. The vicriviroc treatment arms in the Suleiman et al study included 79 participants. Four deaths were reported in the study, including 2 subjects in the placebo group and 2 in the vicriviroc 20 mg treatment group; the latter 2 were attributed to bilateral atypical pneumonia and presumed disseminated tuberculosis, complicated by multiple organ failure. The concept of targeting a human receptor has numerous advantages but is also accompanied by concerns for untoward effects, especially when the receptor blocked is nonspecific for a given pathogen and has an important role in the general function of cellular immunity against other viruses. In the future, the encouraging results of this trial should be followed up by studying additional patients with specific attention to other viral infections and for a longer follow-up period.

Detection of West Nile virus in formalin-fixed, paraffin-embedded human tissues by RT-PCR: A useful adjunct to conventional tissue-based diagnostic methods

Background West Nile virus (WNV), a member of genus Flavivirus, causes febrile illness, encephalitis, meningitis, myelitis, and occasional deaths in humans. Although several reverse transcription-polymerase chain reaction (RT-PCR) assays have been developed for detection of WNV in serum, cerebrospinal fluid, and fresh tissues, the usefulness of WNV RT-PCR assays for RNA extracted from formalin-fixed human tissues has not previously been demonstrated. Objective The objective of this study was to evaluate the application of a RT-PCR technique for the detection of WNV in routinely processed, formalin-fixed, paraffin-embedded (FFPE) human tissues, and to compare it with conventional serology and immunohistochemistry (IHC). Study design We performed two WNV-specific nested RT-PCR assays targeting the viral capsid, premembrane, and envelope genes in FFPE central nervous system tissue samples from 27 patients with fatal WNV encephalitis, as confirmed by serology or IHC, and compared the results. The presence of WNV in RT-PCR-positive samples was confirmed by amplicon sequencing. Results Twenty (74%) patients were WNV RT-PCR positive while 24 (89%) were seropositive. WNV IHC staining of neurons and neuronal processes was positive in fourteen (52%) patients. The concordance between IHC and serology was 41% (11/27) and between RT-PCR and serology was 63% (17/27). All 11 seropositive/IHC-positive patients and 6 (46%) of 13 seropositive/IHC-negative patients were RT-PCR positive while all 3 seronegatives were positive by both IHC and RT-PCR. Conclusions In this study, RT-PCR was significantly more sensitive than IHC in detecting WNV infections and provided specific sequence information about the infecting virus. RT-PCR on FFPE tissues may be a particularly useful diagnostic tool in patients who die relatively soon after disease onset and for whom serology may be negative. Combined use of serology, IHC, and RT-PCR would be expected to have the best overall sensitivity and improve detection of fatal WNV infection.

Chemokine receptor CCR5 mediates resistance to West Nile Virus infection in mouse and man

West Nile Virus (WNV) is a re-emerging pathogen and a well-known agent of fatal encephalitis in several species, including mouse and man; however immunopathogenic mechanisms are poorly understood. We found that WNV induced upregulation of the chemokine receptor/HIV coreceptor CCR5 and its ligand CCL5 in mouse brain, as well as influx of effector leukocytes, including CD4+ and CD8+ T cells, NK cells, and macrophages, of which ~25% expressed CCR5. Infection of CCR5-/- mice was rapidly and uniformly fatal, whereas the majority of CCR5+/+ mice survived. Consistent with this, CCR5 32 homozygotes were overrepresented in three of three cohorts of symptomatic WNV seropositive individuals compared to control populations. And were more likely to have a fatal outcome. CCR5 appears to mediate resistance to fatal WNV infection in mouse and man by coordinating leukocyte recruitment to the infected brain. Thus CCR5 32 homozygosity is a strong genetic risk factor for symptomatic WNV infection in man. The results suggest that therapeutic blockade of CCR5 may carry increased risk of symptomatic and possibly fatal outcome should individuals become infected with WNV.

A genetic basis for human susceptibility to West Nile virus

West Nile virus (WNV) infects thousands of humans annually and causes a spectrum of disease ranging from an acute febrile illness to lethal encephalitis. A new study suggests a link between CCR5Delta32 (a common mutant allele of the chemokine and HIV receptor CCR5) and fatal WNV infection. The study highlights a possible risk in targeting this receptor for the prevention and/or treatment of infectious diseases.

CCR5 thwarts West Nile virus

A genetic mutation that protects against HIV infection increases the risk of developing clinical West Nile virus (WNV) infection, according to Glass and colleagues on page 35. Figure 1 Individuals homozygous for the CCR5Δ32 allele are more likely to suffer from fatal West Nile Virus infection. The mutation in question is a 32-bp deletion in a gene that encodes the chemokine receptor CCR5, which was identified in 1996 as a cellular coreceptor for HIV. Individuals homozygous for this mutation (CCR5Δ32) are highly resistant to HIV infection, even when repeatedly exposed to the virus. This resistance was the theoretical basis for the development of therapeutic CCR5 inhibitors, several of which are now in clinical trials. CCR5 seemed like an ideal drug target, as people missing the receptor were healthy and no diseases or infections were known to be more frequent or severe in individuals homozygous for CCR5Δ32. Mice appeared to be equally unfazed by the lack of CCR5. But new evidence suggests that the lack of CCR5 is not completely innocuous. This group recently showed that infection with WNV—a mosquito-borne virus that has spread rapidly across the United States since 1999, often causing fatal encephalitis—was uniformly fatal in mice lacking CCR5. This finding prompted the group to look for the CCR5Δ32 allele in two cohorts of patients in the United States who had symptomatic WNV infections. They now report that 4–5% of the infected individuals were homozygous for the CCR5Δ32 allele, compared with less than 1% of the general population, suggesting that the lack of CCR5 puts people at risk for developing clinical WNV infections. The magnitude of this risk is comparable to the magnitude of protection against HIV that is conferred by this genotype. It remains to be tested whether CCR5-deficient humans, like mice, develop more severe disease because fewer protective immune cells gain access to the brain. This study identifies not only the first genetic susceptibility factor for WNV infection but also the first association of the CCR5Δ32 allele with susceptibility to an infectious disease. These data might also raise a red flag for the use of CCR5 inhibitors in HIV-infected patients—at least in areas endemic for WNV—as such inhibitors might increase the recipients' vulnerability to severe WNV infection.

Fatal West Nile Virus Infection After Rituximab/Fludarabine–Induced Remission for Non-Hodgkin's Lymphoma

West Nile virus (WNV) infections are potentially life threatening in immunocompromised hosts. Currently, the best diagnostic test is serology. Reverse-transcriptase polymerase chain reaction (RT-PCR) testing has a role, but, because WNV is a cell-associated neurotropic virus, RT-PCR results are frequently negative even in cases of active infection. We present a case in which serology results were persistently negative because the patient was immunocompromised following lymphoma treatment. The role of humoral immunity in resolution of WNV is also discussed.

Fatal West Nile Virus Infection in a White-tailed Deer (Odocoileus virginianus)

A 3-yr-old male white-tailed deer (Odocoileus virginianus) with a history of ataxia and tremors was submitted to the Tifton Veterinary Diagnostic and Investigational Laboratory (The University of Georgia, Tifton, Georgia, USA) for necropsy. Gross findings were unremarkable. Histologically, the brain had multifocal lymphoplasmacytic perivascular inflammation, scattered gliosis, and rare satellitosis. Mild hemorrhage and congestion in the retropharyngeal lymph nodes and mild lymphoid depletion in the tonsil were present. A reverse transcription-polymerase chain reaction test performed on brain yielded a positive result for West Nile virus. This represents the first report of fatal West Nile virus infection in a white-tailed deer.

DNA vaccine for West Nile virus infection in fish crows (Corvus ossifragus).

A DNA vaccine for West Nile virus (WNV) was evaluated to determine whether its use could protect fish crows (Corvus ossifragus) from fatal WNV infection. Captured adult crows were given 0.5 mg of the DNA vaccine either orally or by intramuscular (IM) inoculation; control crows were inoculated or orally exposed to a placebo. After 6 weeks, crows were challenged subcutaneously with 105 plaque-forming units of WNV (New York 1999 strain). None of the placebo inoculated–placebo challenged birds died. While none of the 9 IM vaccine–inoculated birds died, 5 of 10 placebo-inoculated and 4 of 8 orally vaccinated birds died within 15 days after challenge. Peak viremia titers in birds with fatal WNV infection were substantially higher than those in birds that survived infection. Although oral administration of a single DNA vaccine dose failed to elicit an immune response or protect crows from WNV infection, IM administration of a single dose prevented death and was associated with reduced viremia.