3. Co-Infection of Mycoplasma
hyopneumoniae with
bacteria
Pasteurella multocida (PMULT), is a capsulated, Gram-negative
coccobacillus, this primary pathogen can cause debilitating and fatal
porcine pneumonia, especially resulting in pleuritic (Harper, Cox,
Adler, & Boyce, 2011; Ross, 2006). Mhp and PMULT are associated with
pneumonia at both the pig and herd levels, also the coincidental
infections of Mhp and bacteria have also
been
studied for a long period (Fablet, Marois, et al., 2012). In cases with
bacterial pneumonia, PMULT was the most prevalent infectious agent
(Mores et al., 2015; Tocqueville, Kempf, Paboeuf, & Marois-Crehan,
2017), while the co-infection with Mhp and PMULT in gilts and sows can
render the lungs more susceptible to PMULT colonization
and infection(Ciprián, Pijoan, Cruz, Camacho, & Garza, 1988). Though
pigs that have recovered from or vaccinated against Mhp infection were
resistant to PMULT infection (Amass et al., 1994). In addition, Park and
co-workers have elucidated the pathogenic mechanisms through which the
Mhp increases the L-fucose composition to enhance adherence of PMULT
type A to the bronchial and bronchiolar epithelial cells (C. Park et
al., 2016). Moreover, Eileen et al reported that food which contain
doxycycline was effective in fattening pigs to some extent and also
controlling pneumonia which was due to PMULT and Mhp (Bousquet et al.,
1998).
Actinobacillus pleuropneumoniae (APP) is a small, Gram-negative,
encapsulated rod with typical coccobacillary morphology and an
aetiological agent of porcine pleuropneumonia (Sassu et al., 2018).
Concurrent infection with Mhp and APP is common, both of them are
responsible for PRDC (Hege, Zimmermann, Scheidegger, & Stark, 2002).
Mhp and APP are considered to be the most important primary bacterial
respiratory pathogens associated with lung lesions (Fablet, Marois, et
al., 2012), co-inoculation with Mhp and APP can induce more severe
respiratory disorders in pigs (Haimi-Hakala et al., 2017). The detection
rate of 0.1% for APP and 2.6% for Mhp were discovered in 3983 farms
across Switzerland (Hege et al., 2002). Marois and colleagues indicated
that concurrent infection with Mhp and APP had more severe lesions
compared to single does infection in experimental pigs, pigs which were
infected with the APP still remained healthy and lung lesions were only
observed after the co-infection with Mhp(Marois et al., 2009).
Meanwhile, the phagocytic abilities of alveolar macrophage had decreased
in pigs co-infected with Mhp and APP (Caruso & Ross, 1990).
Lawsonia intracellularis(LI)
are Gram-negative, obligate intracellular bacteria that cause
proliferative enteropathy (PE), an economically important disease for
the pig industry(Obradovic & Wilson, 2019). Dual infections with LI and
Mhp caused the epithelial thickening and post-absorptive metabolic
functions altering in pigs that result in reduced nutrient absorption,
reductions in growth performance and feed efficiency (Helm, Curry,
Schwartz, Lonergan, & Gabler, 2019; Helm, Outhouse, Schwartz, Lonergan,
et al., 2018). Helm et al confirmed that, a dual enteric and respiratory
pathogen challenge reduced
average
daily weight gain (ADG), average daily feed intake (ADFI), Gain:Feed
(G:F) and tissue accretion in growing pigs(Helm, Outhouse, Schwartz,
Dekkers, et al., 2018).
Moreover, studies have shown that immunosuppression caused by the
predisposing of Mhp infection, can downregulate the phagocytic response
, causing more serious clinical symptoms through the exposition to other
bacterial pathogens, such as Bordetella bronchiseptica ,Haemophilus parasuis , Trueperella pyogenes and
streptococci or staphylococci in field outbreaks of MPS(Caruso & Ross,
1990; Maes et al., 2018). It was also, reported that concurrent
infections with different Mhp strains have been detected in the same
field (Vranckx et al., 2011; Vranckx, Maes, Sacristan Rdel, Pasmans, &
Haesebrouck, 2012), resulting in higher severity and prevalence of
Mycoplasma-like lung lesions in slaughter pigs (Michiels, Vranckx, et
al., 2017). Annelies and colleagues also demonstrated that, pigs that
were co-infected with highly virulent strain F7.2C and the low virulent
strain F1.12A, showed more severity lung lesions, coughed and larger log
copies of Mhp in the bronchoalveolar lavag (Michiels, Arsenakis, et al.,
2017). However, simultaneous infection with M. hyorhinis and Mhp
did not aggravate the observed lung lesions (Luehrs et al., 2017), the
results indicated that different virulent strain can interact with each
other, but not between different species of mycoplasma. Further studies
is needed to focus on the exact mechanism of how
these bacterial pathogens interact with Mhp.