Sometimes, dogs have positive impacts on psychosocial
and psychical status of their owners compared to others may
be suffering from depression and mental stress . Dogs
are susceptible to several types of infectious diseases can be
worrisome for their owners because some of them are fatal if
not treated soon enough. Bacterial and fungal infections can be
contracted through different parts of body. Furthermore, many of
them are zoonotic infection among humans and dogs. The signs
of any disease typically depend on location of infection either
local infection or systemic infection. The local infection usually
involves the skin surface that look like wounds and swellings
may be appear firm or soft and may be contain discharges. These
discharges depend on consistency and color may be varying from
watery to thick with different color. While systemic infection
depends on affected organ that notice signs such as coughing,
sneezing, diarrhea, loss appetite and loss of weight. The majority
of households keep dogs for many purposes in their life. Thus,
this review focused on an overview of the most common bacterial
and fungal infections found in dogs and clinical signs, and how
they are diagnosed.
Pasteurella is a normally inhabited bacterium in upper
respiratory tract of dogs under normal circumstances. It is a zoonotic disease can be transmitted into human, and have
the most prevalent among animal populations. Pasteurellosis
is systemic bacterial disease and clinically characterized by
respiratory distress and pneumonia.
Etiology and clinical findings
Pasteurella spp. is a small, Gram negative, non motile,
facultative, anaerobic coccobacillus. It cause the endemic disease
in dogs and can be transmitted to human by direct and indirect
contact like dog biting, licking, contact with nasal discharge and
scratches . Pasteurella spp commonly affect the soft tissues
and wounds infections after infection transmission. Therefore,
the manifestation and clinical signs relevant to Pasteurella
infection ranged from mild symptomatic to sever, acute to
chronic infection, often fetal and/or disseminated infections .
Mild symptoms include sneezing, copious mucous secretions,
mild rhinitis, mild pneumonia with labored breathing, and fever
and can be progress to disseminated diseases . Many studies
reported that Pasteurella causes septic arthritis, meningitis,
endocarditis, peritonitis, pneumonia, sepsis and deep-seated
Conventional methods are the most frequently used for
detection and diagnosis of Pasteurellosis. An observation of the
stained bacterium under microscope and isolation on selective
media and followed by serological analysis. The specimens may
be required for examination such as blood sample, nasal swabs.
Microscopic examination of fresh culture or specimens using
Giemsa stain or Leishman’s stain shows bipolar-staining rods.
Pasteurella isolate and grow well at 37°C on selective media
such as 5% sheep’s blood in dextrose-starch, casein-sucroseyeast
(CSY), Mueller-Hinton and brain heart infusion (BHI)
agar. These media were prepared by adding antibiotics like
vancomycin, clindamycin, gentamicin, neomycin, kanamycin,
amikacin either singly or in combination to select for Pasteurella
. Furthermore, biochemically are positive for catalase, oxidase,
indole, and ornithine decarboxylase .
Salmonella is a zoonotic infection and can be transmitted
by many species of animals and human. A member of family Enterobacteriaceae is widely distributed and transmitted either
direct or indirect contact (fecal-oral transmission) . The
main clinical signs of Salmonella are gastrointestinal disorders,
manifested by gastroenteritis, fever and bacteremia.
Etiology and clinical signs
Salmonella spp is Gram negative, anaerobic, non-motile,
bacilli that multiply and colonize in large intestine especially
in distal part of colon and mesenteric lymph nodes. There are
predisposing factors increase the risk of Salmonella including
dog’s age either young or older dog due to their under developed
or/and compromised immune system and administration of
antibiotic therapy for long time that make imbalance between the
beneficial bacteria in GIT and harmful one.
The prevalence of Salmonella in dogs is a highly variable
depending on the environment which the dogs live. For instance,
Salmonella isolates from stray dogs were higher than those
from the household dogs . However, the majority of infected
animals is asymptomatic and can shed the microorganism in
feces for 6 weeks . Therefore, the clinical signs of Salmonella
may be asymptomatic carrier or exhibit variation in clinical signs
depending on the severity of infection. These signs include fever,
diarrhea often bloody, lethargy, depression, loss of appetite and
dehydration but in severe cases may be fatal.
The conventional methods are frequently used for detection
and diagnosis. Sample may be required for Salmonella diagnosis
is the fecal sample. The fecal sample is prepared and cultivated
on specific media like Xylose lysine deoxycholate (XLD) agar,
Hekeon enteric agar and Brilliance Salmonella agar then incubate
for 24h at 37°C to determine the presence of Salmonella.
Serological assays are rapid tests and the most commonly
used for Salmonella diagnosis such as Salmonella agglutination
and Rapid latex agglutination test .
Brucellosis is a contagious zoonotic disease. Brucella canis is
transmitted among dogs by venereal and oral transmission and
reported in human cases had contact with body fluid of infected
dogs. The incubation period of Brucella may last from one week
up to several months . The main clinical signs in dogs is
reproductive problems characterized by abortion in late stage of
pregnancy in female and orchitis, epididymitis and prostatitis in
Etiology and clinical signs
Brucella canis is Gram negative, coccobacilli, faculatative
intracellular bacteria belong to genus Brucella. Other Brucella
species such as B. abortus, B. melitensis and B. suis occasionally
associated with disease in dogs .
Brucellosis has no specific clinical signs but when appear
symptoms, it usually related to reproductive problems. Brucella
canis can cause abortion mostly during the last trimester (45 -
55 days) followed by a mucoid, serosanguinous or gray-green vaginal discharge persist for several weeks or cause early
embryonic deaths or stillbirth frequently die after birth. While in
male dogs may cause epididymitis and scrotal edema and orchitis
in acute stage of infection. Concurrent prostatitis is common
that result to pain and difficulty in urination and defecation.
Lymphadenitis is common and may be regional or generalized in
infected dogs. In case of chronic infection may be occur unilateral
or bilateral testicular atrophy. Some males become infertile due
to morphological abnormalities in sperm and reduced viability.
Occasionally, discospondylitis, chronic uveitis, unilateral
endophthalmitis, dermatitis, endocarditis, osteomyelitis and
meningoencephalitis have been reported [17,18].
Definitive diagnosis of Brucella canis is based on isolation and
identification from the clinical specimens. The specimens may be
required for detection is placenta, vaginal secretion and ejaculate.
These samples are prepared and cultivated on selective media
such as Farrell’s, Thayer-Martin’s or CITA medium. Therefore,
microscopic examination of stained smears from specimens
using modified ZiehlNeelsen staining that show as coccobacilli,
often singly but sometimes in pairs or small groups.
Serological assays are more available and often used to
diagnose the infection of B. canis. The commonly serological tests
used for diagnosis are the rapid slide agglutination test and the
tube agglutination test. As soon as 2-4 weeks after infection some
dogs seroconvert, but others may not have detectable titers until
3-4 months. Therefore, positive results in screening tests should
be confirmed by more specific tests such as ELISAs . Even
PCR tests for Brucella are mainly used to identify organisms in
culture and often used directly in clinical samples .
Yersiniosis is a zoonotic bacterial disease can be transmitted
among animal species and human by direct contact with infected
animals or ingestion of contaminated food and water (fecal-oral
transmission) . This is one of the enteric bacterial diseases
that clinically characterized by acute diarrhea.
Etiology and clinical signs
Yersinia enterocolitica is Gram-negative, faculatative
anaerobic, coccobacillus bacterium belonging to the family of
Enterobacteriaceae. Yersinia enterocolitica subdivided into 5
strains (1A/1B, 2, 3, 4, 5) and 76 serotypes. Some strains of this
species can produce a thermostable enterotoxin . The disease
is manifested and clinically characterized by fever, watery or
bloody diarrhea, abdominal cramps, anorexia and vomiting.
These symptoms may last from 1-3 day up to 3 weeks then occur
self-limiting or may complicated and take place osteomyelitis,
hepato-splenic abscesses, skin ulcers, conjunctivitis, meningitis,
pharyngitis, urinary infections or septicaemia [23-25]. Others
appear without observable symptoms .
have gastroenteritis symptoms. Fecal samples were taken and
prepared for isolation and identification of the causative agent.
Samples were cultivated in yersinia selective agar and incubated
for 24 h at 30°C to isolate Yersinia. Yersinia biochemically
characterized by esculin hydrolysis, indole production, and the
ability to ferment D-xylose and D-trehalose . Serology is used
to detection the infection with Y. enterocolitica is available using
Y. enterocolitica O:3, O:5, O:8, O:9, and O:27 commercial antisera.
Leptospirosis is a widely distributed zoonotic bacterial disease
can be transmitted through direct contact with contaminated soil,
water and urine. Rodents act as a major reservoir for Leptospira
. The incubation period of this disease may be ranged from
2 to 26 days  and the highest incidence is associated with
period of rainfall. Leptospira can affect on many organs such as
liver, kidney and blood vessels and manifested by fever, vomiting
and diarrhea [30, 31].
Etiology and clinical signs
Leptospira is Gram negative aerobic bacterium related
to order Spirochaetales, family Leptospiracae. It is fastidious
bacteria, slow growing and have characteristic corkscrew like
motility. The genus leptospira is divided into two species L.
interrogans and L. biflexa and subdivided into multiple serovars.
Serovars were reported in dogs including icterohaemorrhagiae,
grippotyphosa, bratislava, canicola and pomona .
Leptospirosis may present variety of symptoms and the
common clinical signs appear on dogs including anorexia,
lethargy, vomiting, diarrhea, abdominal or lumbar pain,
musculoskeletal pain and dehydration [33, 34]. Uveitis, renal and
hepatic diseases have been also observed as well as ventricular
tachyarrhythmia may be accompanied with myocardial damage
in some dogs . However, other cases may appear without any
Diagnosis of leptospirosis depends on clinical examination
and vaccination history and laboratory diagnosis. Serological
tests are the most frequently used in diagnosis of leptospira in
dogs that used to detect antibodies against the organism and
also detect the organism in body fluid. Widespread leptospiral
vaccines in dogs complicate interpretation of leptospiral serology.
Generally, vaccinated dogs develop relatively low agglutinating
antibody titers (1:100 to 1:400) in response to vaccination, and
these titers persist for 1–3 months after vaccination. However,
some dogs develop high titers after vaccination which persists
for 6 months. Other diagnostic tests are used such as PCR and
culture but the sample should be collected before antibiotic
administration for maximal sensitivity. Samples may be required
for culture are blood, urine, or tissue samples. These samples
were prepared and cultivated specialized culture medium to
identify the infecting serovar. Blood may be cultured early stage
of infection; but urine may be positive through 7–10 days after
clinical signs appear.
Campylobacterosis is an infectious bacterial disease that
found in intestinal tract of dogs. Campylobacter is usually
transmitted by ingestion of contaminated food and water or
direct contact with contaminated objects. The clinical signs are
characterized by mild to moderate diarrhea.
Etiology and clinical signs
Cambylobacter spp is Gram negative bacteria, spiral in shape
that exhibits a characteristic corkscrew darting motility and
moved by a single polar flagellum. The Cambylobacter jejuni
and C. coli are the highest prevalence and usually result in
campylobacter enteritis in dogs. Dogs and puppies represent
the major reservoirs for campylobacter . The incubation
period of campylobacter varies from one to seven days. Most
infected dogs appear without observable symptoms but, others
show symptoms. The observable clinical signs are often watery
and may be associated with bloody diarrhea, fever, vomiting and
abdominal pain. Some nervous signs including convulsion and
seizure may be observed in some cases .
Diagnosis of Campylobacteriosis depends on isolation of
the causative agent using selective media. The sample may be
required for diagnosis is fresh fecal sample that should be used
for processing within 2 days. Microscopic examination for pure
colonies showed gram-negative and curved rods. Biochemical
tests are used for identify different species including its ability
to hydrolyze hippurate, and negative catalase production.
Furthermore, other diagnostic tests as PCR are used for
identification of infection if the culture is difficult .
Bordetellosis (kennel cough)
Bordetella bronchiseptica is an infectious bacterium that
normally lives in upper respiratory tract. B. bronchiseptica may
be transmitted among dogs living in close places which are
considered one of the most prevalent respiratory infections of
dogs. it is clinically characterized by frequent dry and hacking
coughing with high morbidity and low mortality rate .
Etiology and clinical signs
Bordetella bronchiseptica is Gram negative, aerobic,
coccobacillus bacterium. It belongs to genus Bordetella, and
family Alcaligenaceae. This genus is consisted from nine species
including B. bronchiseptica, B. pertussis, B. parapertussis, B.
parapertussis, B. hinzii, B. avium, B. holmseii, B. trematum and
B. petrii [40, 41]. B. bronchiseptica has been associated with
zoonotic respiratory infections .
There are predisposing factor enhance the virulence and
chance of colonizing this pathogen in respiratory tract associated
with the impairment of immune system, direct cellular injury of
respiratory epithelium . Incubation period ranged from 1
to 8 days and the clinical signs extend for 1–2 weeks. Infected
dogs may shed the pathogen for 2–3 months after recovery.
Bordetellosis have two clinical forms, the first form is a typical and the most common which is associated with dry hacking
cough, gagging and retching behavior in dogs while, the second
form is a complicated and more common in puppies or immuno–
compromised dogs which characterized by wet cough. This
disease is accompanied with mucoid discharges and signs of
systemic infection including pyrexia, anorexia, chorioretinitis,
vomiting and diarrhea in severe cases, finally resulting in death
of the puppies .
Diagnosis of bordetellosis depends on the isolation of the B.
bronchiseptica followed by the identification of the organism by
biochemical tests, serological and molecular methods. Samples
can be taken from nasal swab and throat swab and then prepared
for isolation of Bordetella species which grow readily on blood
agar, Bordet-Gengou agar, Smith-Baskerville culture media and
MacConkey agar at 37°C. Biochemically, Bordetella are positive
for oxidase, catalase and citrate utilization and are negative
for fermentation of any sugar, production of gelatinase, DNase,
indole and H2S .
Serological tests are often considered the best method
to facilitate the diagnosis of Bordetella in case of difficulty
in isolation. Commonly serological tests used for diagnosis
include tube agglutination, indirect haemagglutination, microagglutination
test and ELISA [46,47].
PCR has been exploited to achieve the fast and accurate
detection of Bordetella in clinical samples because the isolation
and identification is a time consuming process and serological
tests have not good specificity .
Coxillosis is a zoonotic bacterial infection that causes Q-fever
in human. Coxiella burnetii infects a wide range of animals
including ruminants, dogs, cats, arthropods mainly ticks, birds
and human. The most common reservoir of C.burnetii are cattle,
sheep and goat as well as, some studies approved that possible
act infected dogs and cats as reservoirs for Q-fever [49, 50]. The
route of transmission of C.burnetii occur through two major
patterns either the organism circulates between animals via
tick bites or by inhalation of contaminated aerosols, ingestion
of contaminated raw milk or food, or direct contact with body
fluid or placenta [51,52]. This disease is clinically characterized
by reproductive disorders.
Etiology and clinical signs
Coxiella burnetii is Gram negative, coccobacillus, obligatory
intracellular bacterium. Previously, it classified as a rickettsial
agent, but recently phylogenetic analyses found that C.burnetii is
more closely related to Legionella and Francisella than to the
genus Rickettsia. It reproduces in phagolysosomes of host
monocytes and macrophages. It has two forms exist: the first is
the large cell variant which is a vegetative form found in infected
cells, while the second is the small cell variant which is the
extracellular infectious form shed in milk, urine, and feces and
found in high concentration in placental tissue and amniotic
fluid. The small cell variant is resistant to heat, drying, and many common disinfectants and remains viable for weeks to years in
the environment . Incubation period may persist from 8 to12
days after exposure to infection. Infection in animals is usually
subclinical and infected cases are asymptomatic. However,
some infected animal showed reproductive disorders including
abortions, stillbirths, retained placenta, infertility, metritis and
weak newborns [54, 55].
Diagnosis of C. burnetii depends on tissue culture of suspected
infected dogs or aborted fetus. Due to difficulty in cultivation,
serological test such as indirect immunofluorescence assay and
ELISA are available for diagnosis of C. burnetii. Serologic testing
is in combination with PCR recommended due to PCR of whole
blood or serum can be positive in very early stages after symptom
onset but becomes negative as the antibody titer increases and
after administration of antibiotics [56,57].
Aspergillosis is an infection caused by the Aspergillus fungus,
which is found worldwide. This infection has two types, nasal
form and disseminated form. Both types can occur in cats and
dogs, but they occur more frequently in dogs. It is primarily
respiratory infection which may become generalized.
Etiology and clinical signs
Aspergillus species is fungus that widely distributed in
environment and has capacity of growing in different substrates.
There are different species cause disease in dogs including
Aspergillus fumigatus, Aspergillus flavus, Aspergillus terreus,
Aspergillus niger and Aspergillus deflectus. Several studies
reported that aspergillosis affects every age, but it primarily
affects young to middle-aged animals . Aspergillosis in dogs
has two forms, nasal aspergillosis is caused predominantly by
Aspergillus fumigates which accompanied with unilateral or
bilateral profuse purulent to mucopurulent nasal discharge,
lethargy, nasal pain, sneezing, ulceration surrounding the nostrils
and open-mouth breathing. Ocular discharge and exophthalmos
may be seen .
Dissimenated aspergillosis is generalized form of infection
that usually caused by Aspergillus tereus, Aspergillus deflectus,
and Aspergillus niger. Infection mostly occurs through entrance
fungus into the respiratory tract and goes to the lungs, then
hematogenous spread into other sites including the intervertebral
discs of the spine or the kidneys and irises as well as other
organs, muscles, and bones. This disease usually take several
months to appear the signs of infection including vertebral pain
progressing to partial or complete paralysis or lameness of a
limb with pronounced swelling, anorexia, weight loss, lethargy,
fever, weakness, vomiting, blood in the urine and lymph node
Definitive diagnosis of aspergillosis depends on isolation
and identification of the fungus through culture. Samples may be acquired from urine, nasal swabs, lymph node aspiration, CSF.
Sample was inoculated on specific media such as Sabouraud’s
dextrose agar (SDA). The isolates were identified on the basis
of morphology and cultural characters . Microscopic
examination for urine and different specimen may be showed
many branching hyphae.
Candida spp are ubiquitous and saprophytic yeast which
widely distributed in a variety of animals. Candidiasis is localized
fungal disease affecting skin and mucous membranes and genital
and gastrointestinal tracts of dogs. There are predisposing
factors such as injury to any of the mucous membranes, the use of
catheters, administration of antibiotics, and immunosuppressive
states help in developing candidosis.
Etiology and clinical signs
Candida spp are normally inhabited in skin, digestive tract,
upper respiratory and genital mucosa of animals. C. albicans and
C. parapsilosis are the most common isolations . Under normal
conditions, these organisms may transform into pathogens
causing different infections and clinical signs may be localized or
generalized. Signs of infection are variable and non specific such
as skin lesions, oral lesions and diarrhea, all may be associated
with predisposing conditions than with the candidiasis itself.
Systemic infection appears with general symptoms according
to affected organs. Peritonitis and chronic cystitis have been
Fungal diagnosis based on morphological and biochemical
characters. Samples may be required from skin lesion and
scraping that were inoculated into Sabouraud’s dextrose agar
at 25 °C. All isolates were examined by direct microscope
for specimens showing ovoid, budding yeast cells with thin
walls, or they occur in chains that produce pseudohyphae
when the blastospores remain attached after budding division.
Filamentous, regular, true hyphae also may be visible . In
addition, the germ tube test with human serum gave a positive
result after 3 hours incubation at 37°C. Biochemically, Candida
albicans is characterized by carbohydrate assimilation.
Dermatophytosis is the most common fungal infection
affecting skin, hair and nails in dogs and cats. It is characterized
by a superficial skin infection confined to keratinized epithelium.
The warm and humid climate is most suitable condition for
infection. This infection is transmitted by direct contact with the
infected animals or with contaminated equipment with fungus
such as grooming equipment. Incubation period of infection may
be developed within 1 to 3 weeks .
Etiology and clinical signs
Dermatophytosis is caused mainly by Microsporum canis,
but M. gypseum and Trichophyton mentagrophytes have been
reported in some cases. Many infected dogs appear without
any signs but may be subclinical infected. When the infection developed the signs appear as a regular and circular alopecia,
with erythematous margin and a thin desquamation. Lesions can
be single or multiple, and are localized on any part of dog and
Multiple lesions may coalesce .
Diagnosis is made by identification of the infection in dogs by
culture and microscopic examination. Wood’s lamp examination
seek for fluorescence on the infected hair shafts with M. canis
but the negative result does not rule out the infection .
Direct microscopic examination of hairs and scales specimens
of infected dogs shows the presence of fungal hyphae and/or
ectothrix spores. This examination is considered very important
in the diagnosis of dermatophytoses.
Definitive diagnosis for Dermatophytosis is done by fungal
culture. Samples may be required from scraping or biopsy
specimens were inoculated into fungal culture media include
Sabouraud’s dextrose agar and dermatophyte test medium .
There are several bacterial and fungal infections are zoonotic
and infectious can infect both human and animals and can be
transmitted by pet animals. Among them, dogs are responsible
for transmission of these infections to their owners. Thus, dog
owners should be had some information regarding to their route
of transmission to reduce these infections and recommended the
preventive methods to avoid these infections and application
food hygiene protocol such as good cooking meat. Furthermore,
the dogs should be fed on good cooked meats to prevent
campylobacter and salmonella infection. In addition, cleaning
the grooming equipment is very important to prevent the fungal
infection and so on. Moreover, the knowledge about clinical
signs and symptoms of each disease and diagnostic methods are
important for treatment, prevention and control, besides public
health problem, because these animals are more inserted in our
daily life, maintaining close contact with us.