Feline immunodeficiency virus is concentrated in milk early in lactation

Milk Transmission of Mammalian Retroviruses

The transmission of viruses from one host to another typically occurs through horizontal or vertical pathways. The horizontal pathways include transmission amongst individuals, usually through bodily fluids or excretions, while vertical transmission transpires from mother to their offspring, either during pregnancy, childbirth, or breastfeeding. While there are more than 200 human pathogenic viruses to date, only a small number of them are known to be transmitted via breast milk, including cytomegalovirus (CMV), human immunodeficiency virus type 1 (HIV-1), and human T cell lymphotropic virus type 1 (HTLV-1), the latter two belonging to the family Retroviridae. Breast milk transmission is a common characteristic among mammalian retroviruses, but there is a lack of reports summarizing our knowledge regarding this route of transmission of mammalian retroviruses. Here, we provide an overview of the transmission of mammalian exogenous retroviruses with a focus on Orthoretrovirinae, and we highlight whether they have been described or suspected to be transmitted through breast milk, covering various species. We also elaborate on the production and composition of breast milk and discuss potential entry sites of exogenous mammalian retroviruses during oral transmission.

Viruses as indicators of contemporary host dispersal and phylogeography: an example of feline immunodeficiency virus (FIVP le ) in free-ranging African lion (Panthera leo)

Measuring contemporary dispersal in highly mobile terrestrial species is challenging, especially when species are characterized by low levels of population differentiation. Directly transmitted viruses can be used as a surrogate for traditional methods of tracking host movement. Feline immunodeficiency virus (FIV) is a species-specific lentivirus, which has an exceptionally high mutation rate and circulates naturally in wild felids. Using samples derived from 35 lion (Panthera leo) prides, we tested the prediction that FIV in lions (FIV_{P le} ) can be used to track the dispersal of individuals between prides. As FIV_{P le} subtypes are geographically structured throughout Africa, we predicted that this marker could be used to detect phylogeographic structure of lions at smaller spatial scales. Phylogenetic analyses of FIV_{P le} pol-RT sequences showed that core pride members (females and subadults) shared evolutionary close viral lineages which differed from neighbouring core prides, whereas sequences from sexually mature males associated with the same pride were always the most divergent. In six instances, natal pride associations of divergent male lions could be inferred, on the assumption that FIV_{P le} infections are acquired during early life stages. Congruence between the genetic pattern of FIV and pride structure suggests that vertical transmission plays an important role in lion FIV dynamics. At a fine spatial scale, significant viral geographic structuring was also detected between lions occurring north of the Olifants River within the Kruger National Park (KNP) and those occupying the southern and central regions. This pattern was further supported by phylogenetic analyses and the confinement of FIV_{P le} subtype E to the northern region of KNP. The study provides new insights into the use of retroviral sequences to predict host dispersal and fine-scale contemporary geographic structure in a social felid species.

Seroprevalence of feline immunodeficiency virus and feline leukaemia virus in Australia: risk factors for infection and geographical influences (2011-2013)

OBJECTIVES

Our aim was to: (i) determine the current seroprevalence of feline immunodeficiency virus (FIV) and feline leukaemia virus (FeLV) in three large cohorts of cats from Australia; and (ii) investigate potential risk factors for retroviral infection.

METHODS

Cohort 1 (n = 2151 for FIV, n = 2241 for FeLV) consisted of cats surrendered to a shelter on the west coast of Australia (Perth, Western Australia [WA]). Cohort 2 (n = 2083 for FIV, n = 2032 for FeLV) consisted of client-owned cats with outdoor access recruited from around Australia through participating veterinary clinics. Cohort 3 (n = 169 for FIV, n = 166 for FeLV) consisted of cats presenting to Murdoch University Veterinary Hospital for a variety of reasons. Fresh whole blood was collected and tested using a commercially available point-of-care lateral flow ELISA kit that detects p27 FeLV antigen and antibodies to FIV antigens (p15 and p24) (cohorts 1 and 2), or one of two lateral flow immunochromatography kits that detect p27 antigen and antibodies to FIV antigen (p24 and/or gp40) (cohort 3). Data recorded for cats in cohort 2 included signalment, presenting complaint and postcode, allowing investigation of risk factors for FIV or FeLV infection, as well as potential geographical 'hot spots' for infection.

RESULTS

The seroprevalence of FIV was 6% (cohort 1), 15% (cohort 2) and 14% (cohort 3), while the seroprevalence of FeLV was 1%, 2% and 4% in the same respective cohorts. Risk factors for FIV infection among cats in cohort 2 included age (>3 years), sex (male), neutering status (entire males) and location (WA had a significantly higher FIV seroprevalence compared with the Australian Capital Territory, New South Wales and Victoria). Risk factors for FeLV infection among cats in cohort 2 included health status ('sick') and location (WA cats were approximately three times more likely to be FeLV-infected compared with the rest of Australia). No geographical hot spots of FIV infection were identified.

CONCLUSIONS AND RELEVANCE

Both FIV and FeLV remain important infections among Australian cats. WA has a higher seroprevalence of both feline retroviruses compared with the rest of Australia, which has been noted in previous studies. A lower neutering rate for client-owned male cats is likely responsible for the higher seroprevalence of FIV infection in WA cats, while the reason for the higher seroprevalence of FeLV in WA cats is currently unknown.

Comparison of risk factors for seropositivity to feline immunodeficiency virus and feline leukemia virus among cats: a case-case study

BACKGROUND

Feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) are reported to have similar risk factors and similar recommendations apply to manage infected cats. However, some contrasting evidence exists in the literature with regard to commonly reported risk factors. In this study, we investigated whether the known risk factors for FIV and FeLV infections have a stronger effect for either infection. This retrospective study included samples from 696 cats seropositive for FIV and 593 cats seropositive for FeLV from the United States and Canada. Data were collected during two cross sectional studies, where cats were tested using IDEXX FIV/FeLV ELISA kits. To compare the effect of known risk factors for FIV infection compared to FeLV, using a case-case study design, random intercept logistic regression models were fit including cats' age, sex, neuter status, outdoor exposure, health status and type of testing facility as independent variables. A random intercept for testing facility was included to account for clustering expected in testing practices at the individual clinics and shelters.

RESULTS

In the multivariable random intercept model, the odds of FIV compared to FeLV positive ELISA results were greater for adults (OR = 2.09, CI: 1.50-2.92), intact males (OR = 3.14, CI: 1.85-3.76), neutered males (OR = 2.68, CI: 1.44- 3.14), cats with outdoor access (OR = 2.58, CI: 1.85-3.76) and lower for cats with clinical illness (OR = 0.60, 95% CI: 0.52-0.90). The variance components obtained from the model indicated clustering at the testing facility level.

CONCLUSIONS

Risk factors that have a greater effect on FIV seropositivity include adulthood, being male (neutered or not) and having access to outdoors, while clinical illness was a stronger predictor for FeLV seropositivity. Further studies are warranted to assess the implications of these results for the management and control of these infections.

Comparison of the geographical distribution of feline immunodeficiency virus and feline leukemia virus infections in the United States of America (2000-2011)

BACKGROUND

Although feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) have similar risk factors and control measures, infection rates have been speculated to vary in geographic distribution over North America. Since both infections are endemic in North America, it was assumed as a working hypothesis that their geographic distributions were similar. Hence, the purpose of this exploratory analysis was to investigate the comparative geographical distribution of both viral infections. Counts of FIV (n=17,108) and FeLV (n=30,017) positive serology results (FIV antibody and FeLV ELISA) were obtained for 48 contiguous states and District of Columbia of the United States of America (US) from the IDEXX Laboratories website. The proportional morbidity ratio of FIV to FeLV infection was estimated for each administrative region and its geographic distribution pattern was visualized by a choropleth map. Statistical evidence of an excess in the proportional morbidity ratio from unity was assessed using the spatial scan test under the normal probability model.

RESULTS

This study revealed distinct spatial distribution patterns in the proportional morbidity ratio suggesting the presence of one or more relevant and geographically varying risk factors. The disease map indicates that there is a higher prevalence of FIV infections in the southern and eastern US compared to FeLV. In contrast, FeLV infections were observed to be more frequent in the western US compared to FIV. The respective excess in proportional morbidity ratio was significant with respect to the spatial scan test (p < 0.05).

CONCLUSIONS

The observed variability in the geographical distribution of the proportional morbidity ratio of FIV to FeLV may be related to the presence of an additional or unique, but yet unknown, spatial risk factor. Putative factors may be geographic variations in specific virus strains and rate of vaccination. Knowledge of these factors and the geographical distributions of these infections can inform recommendations for testing, management and prevention. However, further studies are required to investigate the potential association of these factors with FIV and FeLV.

APOBEC3 proteins expressed in mammary epithelial cells are packaged into retroviruses and can restrict transmission of milk-borne virions

Viruses, including retroviruses like human immunodeficiency virus (HIV) and mouse mammary tumor virus (MMTV), are transmitted from mother to infants through milk. Lymphoid cells and antibodies are thought to provide mammary gland and milk-borne immunity. In contrast, little is known about the role of mammary epithelial cells (MECs). The APOBEC3 family of retroviral restriction factors is highly expressed in macrophages and lymphoid and dendritic cells. We now show that APOBEC3 proteins are also expressed in mouse and human MECs. Lymphoid cell-expressed APOBEC3 restricts in vivo spread of MMTV to lymphoid and mammary tissue. In contrast, mammary gland-expressed APOBEC3 is packaged into MMTV virions and decreases the infectivity of milk-borne viruses. Moreover, APOBEC3G and other APOBEC3 genes are expressed in human mammary cells and have the potential to restrict viruses produced in this cell type. These data point to a role for APOBEC3 proteins in limiting infectivity of milk-transmitted viruses.

Maternal hematological and virological characteristics during early feline immunodeficiency virus (FIV) infection of cats as predictors of fetal infection and reproductive outcome at early gestation

The FIV-infected cat is a small animal model for HIV mother-to-child transmission (MTCT) because the two lentiviruses are biologically related and produce similar clinical syndromes. Both viruses are vertically transmissible and may negatively impact reproductive outcome. Maternal hematological and virological parameters are predictors of MTCT in HIV-infected women. Our purpose was to determine whether similar maternal characteristics during early pregnancy in FIV-infected cats influence pregnancy outcome. We inoculated 10 cats with FIV-B-2542; 10 cats were uninoculated. We quantified longitudinal CD4:CD8 T cell ratios, proviral load, and plasma viremia, monitored longitudinal serostatus, and documented clinical and reproductive outcome during early pregnancy. Inoculated queens were seropositive and provirus positive by week 4 post-infection (p.i.). CD4:CD8 ratios were depressed in the infected group by month 3.5 p.i. Proviral load was variable in the animals throughout the course of infection; plasma viremia was below the level of detection in all animals. Reduced litter sizes and increased fetal demise occurred in infected queens. Viral RNA, but not proviral DNA, was detected in representative placentas (14 of 14; 100%) and fetuses (12 of 14; 86%) collected from infected queens. However, maternal virological and hematological characteristics did not correlate either positively or negatively with reproductive outcome.

FIV cross-species transmission: an evolutionary prospective

Feline and primate immunodeficiency viruses (FIVs, SIVs, and HIV) are transmitted via direct contact (e.g. fighting, sexual contact, and mother–offspring transmission). This dynamic likely poses a behavioral barrier to cross-species transmission in the wild. Recently, several host intracellular anti-viral proteins that contribute to species-specificity of primate lentiviruses have been identified revealing adaptive mechanisms that further limit spread of lentiviruses between species. Consistent with these inter-species transmission barriers, phylogenetic evidence supports the prediction that FIV transmission is an exceedingly rare event between free-ranging cat species, though it has occurred occasionally in captive settings. Recently we documented that puma and bobcats in Southern California share an FIV strain, providing an opportunity to evaluate evolution of both viral strains and host intracellular restriction proteins. These studies are facilitated by the availability of the 2× cat genome sequence annotation. In addition, concurrent viral and host genetic analyses have been used to track patterns of migration of the host species and barriers to transmission of the virus within the African lion. These studies illustrate the utility of FIV as a model to discover the variables necessary for establishment and control of lentiviral infections in new species.

Prevalence of feline immunodeficiency virus infection in domesticated and feral cats in eastern Australia

Serum samples from 340 pet cats presented to three inner city clinics in Sydney Australia, 68 feral cats from two separate colonies in Sydney, and 329 cattery-confined pedigree and domestic cats in eastern Australia, were collected over a 2-year period and tested for antibodies directed against feline immunodeficiency virus (FIV) using immunomigration (Agen FIV Rapid Immunomigration test) and enzyme-linked immunosorbent assay methods (Snap Combo feline leukaemia virus antigen/FIV antibody test kit, IDEXX Laboratories). Western blot analysis was performed on samples in which there was discrepancy between the results. Information regarding breed, age, gender, housing arrangement and health status were recorded for all pet and cattery-confined cats, while the estimated age and current physical condition were recorded for feral cats. The FIV prevalence in the two feral cat populations was 21% and 25%. The majority of FIV-positive cats were male (60-80%). The FIV prevalence in cattery-confined cats was nil. The prevalence of FIV in the pet cat sample population was 8% (27/340) with almost equal prevalence in 'healthy' (13/170) and 'systemically unwell' (14/170) cats. The age of FIV-positive pet cats ranged from 3 to 19 years; all FIV-positive cats were domestic shorthairs with outside access. The median age of FIV-positive pet cats (11 years) was significantly greater than the median age of FIV-negative pet cats (7.5 years: P<0.05). The prevalence of FIV infection in male pet cats (21/172; 12%) was three times that in female pet cats (6/168; 4%; P<0.05). With over 80% of this pet cat population given outside access and continued FIV infection present in the feral population, this study highlights the need to develop rapid, accurate and cost-effective diagnostic methods that are not subject to false positives created by concurrent vaccination against FIV. This is especially important in re-homing stray cats within animal shelters and monitoring the efficacy of the new vaccine, which has not been challenged against Australian strains. The absence of FIV within cattery-confined cats highlights the value in routine screening and indoor lifestyles. This study provides cogent baseline FIV prevalences in three cat subpopulations which can be used for appraising potential disease associations with FIV in Australia.

New challenges for the diagnosis of feline immunodeficiency virus infection

Vaccination of cats against feline immunodeficiency virus (FIV) with a whole-virus vaccine results in rapid and persistent production of antibodies that are indistinguishable from those used for diagnosis of FIV infection. There are no diagnostic tests available for veterinary practitioners at the present time to resolve the diagnostic dilemma posed by use of whole-virus vaccines for protection of cats against FIV. There is a great need for development of commercially available rapid diagnostic tests that conform to differentiation of infected from vaccinated animals standards.

Immunopathogenesis of feline immunodeficiency virus infection in the fetal and neonatal cat

The global incidence of pediatric HIV infection is estimated at 2.3 million children, most acquiring the infection from their mothers in utero, peripartum, or postpartum. Pediatric HIV infection typically causes a rapidly progressive disease when compared with adult infection, due in part to the profound susceptibility of the neonatal thymus to productive infection or degenerative changes. Failed production of naive T-lymphocytes further limits the success of antiviral therapy to restore immunologic function. In this review, we explore the use of feline immunodeficiency virus (FIV) infection of domestic cats as an animal model for pediatric HIV infection. Cats infected with FIV represent the smallest host of a naturally occurring lentivirus, and the immunodeficiency syndrome elicited by FIV infection is similar to that of HIV-AIDS. The feline-FIV model uniquely reproduces several key aspects of immunosuppressive lentivirus infection of the thymus, allowing investigators to define viral determinants of pathogenicity, influence of host age on disease outcome, and therapeutic strategies to restore thymus function.

FIV as a Model for HIV: An Overview

Animal models for human immunodeficiency virus (HIV) infection play a key role in understanding the pathogenesis of AIDS and the development of therapeutic agents and vaccines. As the only lentivirus that causes an immunodeficiency resembling that of HIV infection, in its natural host, feline immunodeficiency virus (FIV) has been a unique and powerful model for AIDS research. FIV was first described in 1987 by Niels Pedersen and co-workers as the causative agent for a fatal immunodeficiency syndrome observed in cats housed in a cattery in Petaluma, California. Since this landmark observation, multiple studies have shown that natural and experimental infection of cats with biological isolates of FIV produces an AIDS syndrome very similar in pathogenesis to that observed for human AIDS. FIV infection induces an acute viremia associated with Tcell alterations including depressed CD4 :CD8 T-cell ratios and CD4 T-cell depletion, peripheral lymphadenopathy, and neutropenia. In later stages of FIV infection, the host suffers from chronic persistent infections that are typically self-limiting in an immunocompetent host, as well as opportunistic infections, chronic diarrhea and wasting, blood dyscracias, significant CD4 T-cell depletion, neurologic disorders, and B-cell lymphomas. Importantly, chronic FIV infection induces a progressive lymphoid and CD4 T-cell depletion in the infected cat. The primary mode of natural FIV transmission appears to be blood-borne facilitated by fighting and biting. However, experimental infection through transmucosal routes (rectal and vaginal mucosa and perinatal) have been well documented for specific FIV isolates. Accordingly, FIV disease pathogenesis exhibits striking similarities to that described for HIV-1 infection.

Feline immunodeficiency virus neuropathogenesis: from cats to calcium

Invasion of human immunodeficiency virus (HIV) into the central and peripheral nervous system produces a wide range of neurological symptoms, which continue to persist even with adequate therapeutic suppression of the systemic viremia. The development of therapies designed to prevent the neurological complications of HIV require a detailed understanding of the mechanisms of virus penetration into the nervous system, infection, and subsequent neuropathogenesis. These processes, however, are difficult to study in humans. The identification of animal lentiviruses similar to HIV has provided useful models of HIV infection that have greatly facilitated these efforts. This review summarizes contributions made from in vitro and in vivo studies on the infectious and pathological interactions of feline immunodeficiency virus (FIV) with the nervous system. In vivo studies on FIV have provided insights into the natural progression of CNS disease as well as the contribution of various risk factors. In vitro studies have contributed to our understanding of immune cell trafficking, CNS infection and neuropathogenesis. Together, these studies have made unique contributions to our understanding of (1) lentiviral interactions at the blood-cerebrospinal fluid (CSF) barrier within the choroid plexus, (2) early FIV invasion and pathogenesis in the brain, and (3) lentiviral effects on intracellular calcium deregulation and neuronal dysfunction. The ability to combine in vitro and in vivo studies on FIV offers enormous potential to explore neuropathogenic mechanisms and generate information necessary for the development of effective therapeutic interventions.

Going wild: lessons from naturally occurring T-lymphotropic lentiviruses

Over 40 nonhuman primate (NHP) species harbor species-specific simian immunodeficiency viruses (SIVs). Similarly, more than 20 species of nondomestic felids and African hyenids demonstrate seroreactivity against feline immunodeficiency virus (FIV) antigens. While it has been challenging to study the biological implications of nonfatal infections in natural populations, epidemiologic and clinical studies performed thus far have only rarely detected increased morbidity or impaired fecundity/survival of naturally infected SIV- or FIV-seropositive versus -seronegative animals. Cross-species transmissions of these agents are rare in nature but have been used to develop experimental systems to evaluate mechanisms of pathogenicity and to develop animal models of HIV/AIDS. Given that felids and primates are substantially evolutionarily removed yet demonstrate the same pattern of apparently nonpathogenic lentiviral infections, comparison of the biological behaviors of these viruses can yield important implications for host-lentiviral adaptation which are relevant to human HIV/AIDS infection. This review therefore evaluates similarities in epidemiology, lentiviral genotyping, pathogenicity, host immune responses, and cross-species transmission of FIVs and factors associated with the establishment of lentiviral infections in new species. This comparison of consistent patterns in lentivirus biology will expose new directions for scientific inquiry for understanding the basis for virulence versus avirulence.

Feline lentiviruses demonstrate differences in receptor repertoire and envelope structural elements

Feline immunodeficiency virus (FIV) causes fatal disease in domestic cats via T cell depletion-mediated immunodeficiency. Pumas and lions are hosts for apparently apathogenic lentiviruses (PLV, LLV) distinct from FIV. We compared receptor use among these viruses by: (1) evaluating target cell susceptibility; (2) measuring viral replication following exposure to specific and non-specific receptor antagonists; and (3) comparing Env sequence and structural motifs. Most isolates of LLV and PLV productively infected domestic feline T cells, but differed from domestic cat FIV by infecting cells independent of CXCR4, demonstrating equivalent or enhanced replication following heparin exposure, and demonstrating substantial divergence in amino acid sequence and secondary structure in Env receptor binding domains. PLV infection was, however, inhibited by CD134/OX40 antibody. Thus, although PLV and LLV infection interfere with FIV superinfection, we conclude that LLV and PLV utilize novel, more promiscuous mechanisms for cell entry than FIV, underlying divergent tropism and biological properties of these viruses.

Vitamin A, Mastitis, and Mother-to-Child Transmission of HIV-1 through Breast-feeding: Current Information and Gaps in Knowledge

Mastitis has been implicated as a risk factor for mother-to-child transmission (MTCT) of HIV-1 through breast-feeding. Maternal vitamin A deficiency is also associated with increased MTCT, as well as with episodes of mastitis in lactating animals. This review describes the complex interrelationship between vitamin A, mastitis, and MTCT of HIV-1 via mothers' milk. Current gaps in knowledge, as well as recommendations for future research efforts, are also discussed.

Effects of passive transfer of immunity on results of diagnostic tests for antibodies against feline immunodeficiency virus in kittens born to vaccinated queens

OBJECTIVE

To determine whether passive transfer of immunity affects results of diagnostic tests for antibodies against FIV in kittens born to vaccinated queens.

DESIGN

Experimental trial.

ANIMALS

12 specific-pathogen-free queens and their 55 kittens.

PROCEDURE

Queens were vaccinated with a whole-virus FIV vaccine prior to breeding. Serum was obtained from the queens on the day of parturition and from the kittens on days 2 and 7, then weekly until results of tests for antibodies against FIV were negative for 2 consecutive weeks. Milk was collected from the queens daily for the first week and then weekly. Serum and milk were tested for antibodies against FIV with 2 commercial assays.

RESULTS

Antibodies against FIV were detected in serum obtained from the queens on the day of parturition and in the milk throughout lactation. All kittens tested positive for antibodies against FIV at 2 days of age. At 8 weeks of age, 30 (55%) kittens tested positive with 1 of the commercial assays, and 35 (64%) tested positive with the other. All kittens tested negative for antibodies against FIV by 12 weeks of age.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggest that kittens readily absorb antibodies against FIV in colostrum from vaccinated queens and that these antibodies may interfere with results of commercially available tests for FIV infection past the age of weaning. Currently licensed diagnostic tests for FIV infection are unable to distinguish among kittens with antibodies against FIV as a result of infection, passive transfer from infected queens, and passive transfer from vaccinated queens.