3 RESULTS AND DISCUSSION
A
total of 1,326
samples
collected from 16
cities
(Figure. 1) geographically located from the north to the south of China
( within the east longitude of 106°55′ to 126°53′ and north latitude of
20°1′ to 45.8′) were detailed in Table 2, and
79.9%
(1060/1326)
of cats were exposed to at least one pathogen of the six viruses.
In details, the
positive rates of cat exposure to
FeLV, FPV, FHV-1, FCV, FIV and FIPV were 59.6%, 19.2%, 16.3%, 14.2%,
1.5% and 0.5%, respectively (Figure 2). The highest ratio of FeLV
infection may be caused by lacking the utilization of FeLV vaccine in
China. The prevalence vary widely depending on the geographical
location
(Gleich,
Krieger, & Hartmann, 2009). A previous report showed a FeLV positive
ratio of 11.33% in Gansu province of northwest China, which was lower
than that in our study. Highly variable prevalence
(1%~12.2%) of FeLV infection in cats have been
reported worldwide (Bande et al., 2012;
Chang et al., 2010;
Dorny et al., 2002;
Gates, Vigeant, & Dale, 2017;
Malik et al.,
1997). The geographical location,
sample quantity and populations may contribute to the variation
(Chang et al., 2010). The prevalence of
FeLV is 52.5% in male and 40.1% in female in this study, which is
consistent with the results of a higher prevalence in male than female
in previous reports (Gleich et al., 2009;
Levy, Scott, Lachtara, & Crawford, 2006;
Norris et al., 2007).The positivity of
FeLV infection was higher in male cats than that in female cats, which
might attribute to the greater risk of bite wounds in males caused by
higher aggressivity.
FPV clinically important in cats with high mortality. Here, the
FPV positivity in China is 19.2%
from 2016 to 2019, which is lower than that (37.1%) in a previous
report of Northeast China from 2016 to 2017
(Niu et al., 2018). Yet, little is known
about the prevalence of FPV of cat in other parts of China and other
countries.
As the main pathogens of upper respiratory tract infection in cats
(Binns et al., 2000), the prevalence of
FHV-1 and FCV (16.3% and 14.2%, respectively) in our study were lower
than that reported in Beijing (26.3% and 46.3%, respectively)
(Xu et al., 2017) and in Switzerland
(20% and 45% in suspect population, respectively)
(Berger et al., 2015).
FIV is distributed worldwide, and
the prevalence of FIV was 2.5% and 5.4% to 31.1% in North America and
Asian (Bande et al., 2012;
Eckstrand, Sparger, & Murphy, 2017;
Levy et al., 2006;
Nakamura et al., 2010;
Phillips, Lamont, Konings, Shacklett, &
Elder, 1992), while it is higher than that in our study (1.5%).
Different detection methods may contribute to the difference. The
false-positive of antibody tests may own to maternal antibodies or
previous FIV vaccination, as the maternal antibodies may persist for 6
months or longer (Barr, Pough, Jacobson, &
Scott, 1991).
FIPV, one of the feline coronavirus (FCoV), is the pathogen of FIP, a
fatal, immune-mediated disease in wild and domestic cats.
FCoVs
are classified into two serotypes, type I and type II. There are two
types of FCoVs, FECV and FIPV, which classified based on pathogenicity.
FECVs produce mild enteric infections
(Pedersen, 1983), and can be converted
into FIPV, and they exist in both serotypes I and II
(Tekes & Thiel, 2016). Previous study
showed a significant higher prevalence rate (74.6%) for FIPV in China
(Li
et al.,
2019)
than than in our study (0.5%), which may be caused by the limited
sampling location.
In all the 1,326 samples,
1,060
(79.9%, 1060/1326) were positive for at least one viral pathogen in
nucleotide detection. As shown in Figure 3, 64.34% (682/1060) of cats
were infected with single type of virus, and
35.66%
(378/1060) of cats were
mixed
infection. The high complexity of mixed infection, more than 10 kinds of
mixed infection patterns as
detected, indicated the
complexity
of viral infectious diseases of cats, it is a challenge for the diagnose
of cat infectious diseases in China.
In
our study, the correlation between positive rate of cats and specific
factors, including age, weather and geographical location, were
analyzed.
The
prevalence
of
FeLV,
FHV-1, FPV and FIV was highly
seasonal (Table
3).
The prevalence
of
FHV-1, FPV and FIV in cold
seasons
(spring
and winter) was higher than that in warm seasons (summer and autumn),
while
an opposite pattern of the prevalence in FeLV could be found. The
positive
rates of FPV, FHV-1, and
FIV
infections of cats in
north
China
(FPV, 21.2%; FHV-1, 18.4%;
FIV,
1.9%) were higher than that
in
south China (FPV, 10.7%; FHV-1, 7.5%; FIV, 0.0%), except that the
FeLV showed an opposite pattern of infection (north China, 51.8%; south
China, 92.5%). As shown in Table 4, the
prevalence of FCV was the same in
north and south China
(14.2%).
FPV
infection
was
age-related
in cats (age <12 months), while the prevalence of FeLV, FHV-1,
FCV was age-irrelevant (Table 5), which varies from previous reports in
New Zealand, where the susceptibility of FeLV decreased significantly
with age
(Luckman
& Gates, 2017).
A total of 316 serum samples of
cats were collected from
four
cities of China (Beijing, Tianjin, Qingdao and Zhengzhou). Antibodies
against FPV were detected by HI assay, and FCV and FHV-1 antibodies were
detected by virus neutralization (VN) assay. The protective titers were
settled as 1:40, 1:32, and 1:16 for
FPV,
FCV, and FHV-1, respectively (Reese et
al., 2008). As shown in Figure 4,
a total of 267
serum
samples of vaccinated cats (Feline Rhinotracheitis- Calici-Panleukopenia
Vaccine, Killed Virus) were analyzed by HI assay for FPV antibodies
detection, and the protective rate was
83.9%
(224/267).
As shown in Table 6, the seroprevalences of FCV and FHV-1 were 58.3%
(151/259) and 44.0% (88/200) by VN assay,
respectively.
The
lower seroprevalences in vaccinated cats indicated an insufficient
potency based on current
commercial
vaccines to against the challenge of wild strains of FPV, FCV, and
FHV-1. The abroad commercial vaccines utilized in China could not resist
the infection of the domestic wild
strains.
In the 39 serum samples of unvaccinated cats, the seroprevalences of
FHV-1, FCV and FPV were 58.6% (17/29), 82.4% (28/34), and 76.9%
(30/39),
respectively (Table 6), higher than that reported in Milan (37.1%,
85.4%, and 45.7%, respectively.)
(Dall’Ara et al., 2019). Another study in
Beijing found that 47.6% of cats were FHV-1 positive by ELISA, but the
vaccination status of these cats was unknown
(Wang et al., 2014). The prevalence of
FHV-1 and FPV in Costa Rica were 71.9% and 92.8%, while only 25% and
16.5% of them were previously vaccinated with FHV-1 and FPV,
respectively (Blanco, Prendas, Corte,
Jimenez, & Dolz, 2009). The seroprevalences of FHV-1, FCV and FPV were
higher than the antigen positive rates, which might be caused by the
recovery of cat and then the undetectable of the antigens of FHV-1, FCV
and FPV.
In
conclusion, six main viral infectious diseases were investigated in cat
population of China, the most widespread virus in cat population is
FeLV, followed by FPV, FHV, FCV, FIV and FIPV. The complexity of cat
mix-infection in China suggested the big challenge for the diagnosis and
treatment of these diseases. Our data also revealed that insufficient
potency by immunization of current commercial vaccines could not give
full protection to wild strains infections of FHV-1, FPV and FCV in
China, demonstrating the urgency of improvement of immune strategies and
the development of new vaccines.