Mycoplasma suis infection results endothelial cell damage and activation: new insight into the cell tropism and pathogenicity of hemotrophic mycoplasma

Haemotrophic Mycoplasmas Infecting Pigs: A Review of the Current Knowledge

Haemotrophic mycoplasmas (haemoplasmas) are a group of highly specific and adapted bacteria. Three different haemoplasma species in pigs are known to date: Mycoplasma (M.) suis, M. parvum and 'Candidatus (Ca.) M. haemosuis'. Even though these bacteria have been known in pig farming for a long time, it is difficult to draw general conclusions about the relevance of their infections in pigs. This review summarizes the current knowledge on the three porcine haemoplasma species with regards to clinical and pathological descriptions, pathobiology, epidemiology and diagnostics as well as prevention and therapy. Overall, it is clear that considerably more data are available for M. suis than for the other two species, but generally, porcine haemoplasmas were found to be highly prevalent all over the world. Mycoplasma suis is the most virulent species, causing acute infectious anaemia in pigs (IAP), whereas M. parvum usually results in chronic and subclinical infections associated with performance losses. Little is known about the clinical significance of the recently discovered third porcine species 'Ca. M. haemosuis'. So far, the described pathogenic mechanisms mainly include direct destruction of erythrocytes via adhesion, invasion, eryptosis and nutrient scavenging, indirect erythrocyte lysis due to immune-mediated events and immune dysregulation processes. A review of published diagnostic data confirms PCR assays as the current standard method, with various cross-species and species-specific protocols. Overall, there is a need for further examination to obtain valuable insights for practical application, specifically regarding the importance of subclinical infections in naturally infected animals. An essential requirement for this will be to gain a more comprehensive understanding of the mechanisms operating between the host and the pathogen.

Porcine ear necrosis: characterization of lesions and associated pathogens

Porcine ear necrosis (PEN) is characterized by ulcerative lesions of the ear auricle. To investigate that problem, three farms with PEN in nursery pigs were included, and the study aim was to characterize PEN and the potential role of pathogens and mycotoxins. Within each farm, one batch of weaned piglets was included and the prevalence and severity of PEN were monitored for 6-7 weeks. Within each batch, 30 PEN-affected/non-affected animals were randomly selected. Blood samples were taken from these animals, to assess the systemic presence of pathogens and mycotoxins, as well as punch biopsies from the ear auricle for histopathological examination. From 10 animals, scrapings and swabs from the lesions were subjected to nanopore metagenomic sequencing and bacteriological cultivation, respectively. In all three farms, lesions appeared within 3-4 weeks post-weaning. The prevalence at the end of the nursery was 33%, 24%, and 46% for farms A, B, and C, respectively. Most affected pigs had mild to moderate lesions. Blood samples revealed low to very low levels of pathogens and mycotoxins. Different bacteria such as Staphylococcus, Streptococcus, Fusobacterium, Mycoplasma, and Clostridium species were identified by sequencing in the scrapings. The first two pathogens were also most often identified in bacterial cultures. Mycoplasma hyopharyngis was only found in PEN-affected pigs. Histopathological changes were primarily observed in the outer layer of the epidermis. The results suggest that PEN lesions develop by damage to the outer part of the skin e.g. by ear suckling or biting, followed by multiplication of opportunistic pathogens.

Mycoplasmas as Host Pantropic and Specific Pathogens: Clinical Implications, Gene Transfer, Virulence Factors, and Future Perspectives

Mycoplasmas as economically important and pantropic pathogens can cause similar clinical diseases in different hosts by eluding host defense and establishing their niches despite their limited metabolic capacities. Besides, enormous undiscovered virulence has a fundamental role in the pathogenesis of pathogenic mycoplasmas. On the other hand, they are host-specific pathogens with some highly pathogenic members that can colonize a vast number of habitats. Reshuffling mycoplasmas genetic information and evolving rapidly is a way to avoid their host's immune system. However, currently, only a few control measures exist against some mycoplasmosis which are far from satisfaction. This review aimed to provide an updated insight into the state of mycoplasmas as pathogens by summarizing and analyzing the comprehensive progress, current challenge, and future perspectives of mycoplasmas. It covers clinical implications of mycoplasmas in humans and domestic and wild animals, virulence-related factors, the process of gene transfer and its crucial prospects, the current application and future perspectives of nanotechnology for diagnosing and curing mycoplasmosis, Mycoplasma vaccination, and protective immunity. Several questions remain unanswered and are recommended to pay close attention to. The findings would be helpful to develop new strategies for basic and applied research on mycoplasmas and facilitate the control of mycoplasmosis for humans and various species of animals.

Occurrence of 'Candidatus Mycoplasma haemosuis' in fattening pigs, sows and piglets in Germany using a novel gap-based quantitative real-time PCR assay

Background

The appearance of the novel porcine haemotrophic mycoplasma (HM) species ‘Candidatus Mycoplasma haemosuis’ was reported in apparently healthy but also in clinically sick animals in China, Korea and in a case report from Germany. Outside of Asia, however, nothing further is known about the frequency of ‘Ca. M. haemosuis’ in pigs to date. To investigate the distribution of this novel HM species in Germany, fattening pigs, sows and pre-suckling piglets were examined using a herein developed quantitative real-time PCR assay (qPCR). Because the piglets were sampled before the first colostrum uptake, additional information on a possible vertical transmission from dams to their offspring was obtained.

Results

Our novel qPCR assay successfully detected ‘Ca. M. haemosuis’ in all blood samples from the ‘Ca. M. haemosuis’-infected pigs. No cross-reactivity was detected when DNA from non-target Mycoplasma spp. and other bacterial species representing 10⁵ bacteria/reaction were used as a template. The lower limit of detection of the qPCR was thus 10 gap gene copies per reaction and 2.5 x 10³ genome equivalents (GE) per mL blood.

‘Candidatus M. haemosuis’ was detected by this qPCR in blood samples from a total out of 6.25% sows (13/208), 4.50% pre-suckling piglets (28/622) and 17.50% fattening pigs (35/200). On farm level, 3 out of 21 piglet producing farms (14.28%) and 9 out of 20 fattening farms (45.00%) were positive for ‘Ca. M. haemosuis’. Co-infections with M. suis were evident in all age groups.

Conclusion

‘Candidatus M. haemosuis’ infection is present in German pig farms and the detection of the novel porcine HM species in piglets immediately after birth before colostrum intake indicates vertical transmission. The novel qPCR assay specific for ‘Ca. M. haemosuis’ described herein will be a prerequisite for future studies on the prevalence, epidemiology as well as the clinical and economic impact of ‘Ca. M. haemosuis’ infections.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-022-03147-1.

Mycoplasma suis Alpha-Enolase Subunit Vaccine Induces an Immune Response in Experimental Animals

Recombinant protein technology has emerged as an excellent option for vaccine development. However, prior to our study, the immune induction ability of recombinant Mycoplasma suis alpha-enolase (rMseno) in animals remained unclear. The purpose of this study was to develop a rMseno protein subunit vaccine and to determine its ability to elicit an immunological response. To accomplish this, we cloned the gene into pET-15b, expressed it in BL21 cells, and purified it. Following the establishment of immunity, the immunogenicity and potential for protection of rMseno were evaluated in mice and piglets. The results demonstrate that anti-M. suis serum recognized the pure rMseno protein in both mice and piglets as evidenced by high levels of specific anti-rMseno antibodies, significantly increased levels of IFN-γ and IL-4 cytokines, and significantly increased T lymphocyte proliferation index. Piglets also had significantly increased levels of specific IgG₁, IgG_2a, CD4⁺, and CD8⁺ cells. The rMseno findings demonstrated a robust immunological response in mice and piglets, affording partial clinical protective efficacy in piglets.

Update on shedding and transmission routes of porcine haemotrophic mycoplasmas in naturally and experimentally infected pigs

Horizontal transmission of Mycoplasma suis via parenteral exposure during standard practices or through bites during fightings have been identified as key epidemiological routes. However, as knowledge gaps on other potential shedding and transmission routes exist, the present study combines both laboratory experiments and field surveys to gain new insights into the epidemiology of porcine haemotrophic mycoplasmas. Splenectomised pigs were orally inoculated with a M. suis field strain and investigated for clinical signs related to infectious anaemia of pigs (IAP) and the presence of M. suis in blood, urine and saliva samples by qPCR. All blood samples were negative for M. suis and animals did not show obvious clinical signs of IAP throughout the entire study period. Additionally, urine, nasal and saliva samples from sows of conventional piglet producing farms and semen samples from a boar stud revealed no detection of M. suis and ‘Candidatus Mycoplasma haemosuis’ by qPCR. Thus, the results indicate that blood-independent transmission routes might be of minor relevance under field conditions.

Clinical, haematological and pathomorphological findings in Mycoplasma suis infected pigs

BACKGROUND

Mycoplasma suis (M. suis) belongs to the group of haemotrophic mycoplasmas and is known as the causative agent of infectious anaemia in pigs. In the last few years valuable insights into the mechanism of adhesion and invasion, shedding patterns and cell tropism of M. suis were gained by the use of new molecular techniques. However, details on M. suis induced lesions as well as the distribution of M. suis in different organs are still lacking. Therefore, seven splenectomised pigs were experimentally infected and clinical and laboratory investigations as well as a detailed histopathological examination were performed. Detection and quantification of M. suis DNA in blood and various tissue samples was done using a quantitative real-time PCR.

RESULTS

During the course of experimental infection, periodically occurring signs of infectious anaemia of pigs including severe icteroanaemia, fever, apathy and anorexia were observed. In addition, dermatological manifestations such as haemorrhagic diathesis presenting as petechiae occurred. The most important haematological alterations were normochromic, normocytic anaemia, hypoglycaemia as well as increased bilirubin and urea concentrations. Necropsy revealed predominant evidence of haemolysis with consecutive anaemia, as well as disseminated intravascular coagulation. M. suis was found in all investigated tissues with the highest copy numbers found in the kidneys. In Giemsa stained sections M. suis was only detected red blood cell (RBC)-associated.

CONCLUSION

In the present study, no RBC independent sequestration of M. suis was detected in organs of experimentally infected pigs. Pathological findings are most likely resulting from haemolysis, consecutive anaemia as well as from disseminated intravascular coagulation and subsequent organ impairments.

Infection strategies of mycoplasmas: Unraveling the panoply of virulence factors

Mycoplasmas, the smallest bacteria lacking a cell wall, can cause various diseases in both humans and animals. Mycoplasmas harbor a variety of virulence factors that enable them to overcome numerous barriers of entry into the host; using accessory proteins, mycoplasma adhesins can bind to the receptors or extracellular matrix of the host cell. Although the host immune system can eradicate the invading mycoplasma in most cases, a few sagacious mycoplasmas employ a series of invasion and immune escape strategies to ensure their continued survival within their hosts. For instance, capsular polysaccharides are crucial for anti-phagocytosis and immunomodulation. Invasive enzymes degrade reactive oxygen species, neutrophil extracellular traps, and immunoglobulins. Biofilm formation is important for establishing a persistent infection. During proliferation, successfully surviving mycoplasmas generate numerous metabolites, including hydrogen peroxide, ammonia and hydrogen sulfide; or secrete various exotoxins, such as community-acquired respiratory distress syndrome toxin, and hemolysins; and express various pathogenic enzymes, all of which have potent toxic effects on host cells. Furthermore, some inherent components of mycoplasmas, such as lipids, membrane lipoproteins, and even mycoplasma-generated superantigens, can exert a significant pathogenic impact on the host cells or the immune system. In this review, we describe the proposed virulence factors in the toolkit of notorious mycoplasmas to better understand the pathogenic features of these bacteria, along with their pathogenic mechanisms.

Persistence in Livestock Mycoplasmas—a Key Role in Infection and Pathogenesis

Purpose of Review

Mycoplasma, economically important pathogens in livestock, often establishes immunologically complex persistent infections that drive their pathogenesis and complicate prophylaxis and therapy of the caused diseases. In this review, we summarize some of the recent findings concerning cellular and molecular persistence mechanisms related to the pathogenesis of mycoplasma infections in livestock.

Recent Findings

Data from recent studies prove several mechanisms including intracellular lifestyle, immune dysregulation, and autoimmunity as well as microcolony and biofilm formation and apoptosis of different host cell types as important persistence mechanisms in several clinically significant Mycoplasma species, i.e., M. bovis, M. gallisepticum, M. hyopneumoniae, and M. suis.

Summary

Evasion of the immune system and the establishment of persistent infections are key features in the pathogenesis of livestock mycoplasmas. In-depth knowledge of the underlying mechanisms will provide the basis for the development of therapy and prophylaxis strategies against mycoplasma infections.

Detection of a novel haemoplasma species in fattening pigs with skin alterations, fever and anaemia

BACKGROUND

In a fattening farm in Southern Germany, skin alterations (urticaria, haemorrhagic diathesis) and high fever were observed in 30% of the pigs 2 weeks after arrival. Feed intake was severely compromised in affected pigs.

METHODS

After detailed clinical observation, blood samples from affected pigs were collected for haematological, PCR and serological investigations. In addition, pathological investigations were performed on one pig.

RESULTS AND CONCLUSION

Analysis of blood parameters revealed a normocytic, normochromic anaemia. A novel porcine haemoplasma species was detected in blood samples of affected pigs and spleen sample of the necropsied pig by PCR. Phylogenetic analyses based on the 16S rDNA showed 99% identity to a novel porcine haemoplasma ('Candidatus (Ca.) M. haemosuis') species which has recently been described in China. Interestingly, this is the first report of 'Ca. M. haemosuis' in pigs with clinical signs resembling those of Mycoplasma (M) suis and the first description of this novel haemoplasma species outside Asia. On-farm affected pigs were treated with oxytetracycline and non-steroidal anti-inflammatory drugs. Clinical signs improved after implementation of treatment and optimisation of management procedures. This case might indicate that other porcine haemoplasma species than M suis can induce fever and skin alterations and may have an economic impact on affected farms.

Detection of Mycoplasma suis in pre-suckling piglets indicates a vertical transmission

Background

Transmission of Mycoplasma (M.) suis mainly occurs via iatrogenic or zootechnical manipulations or due to ranking fights. Other transmission routes including ingestion of secretes/excretes; blood-sucking arthropods and intra-uterine transmission have thought to play an epidemiological role without being experimentally proven. To investigate a vertical transmission of M. suis under field conditions blood samples from pre-suckling piglets and their corresponding dam were examined for M. suis by quantitative polymerase chain reaction (qPCR) in 21 farms in Southern Germany.

Results

A total of 14.35% of the 474 blood samples from pre-suckling piglets reacted qPCR positive. Additionally, M. suis was detected in 65 (31.25%) of the 208 sows at farrowing. On farm level, 16 (76.2%) of the 21 farms had at least one M. suis positive animal. M. suis positive farms had an average of 0.41 more stillborn piglets per litter than M. suis negative farms (p = 0.007).

Conclusion

The present study provides further insights into M. suis infection dynamics as it is the first detection of M. suis in piglets immediately after birth prior to colostrum intake and the first large scale investigation of M. suis in sows at farrowing.

Extra-pulmonary diseases related to Mycoplasma pneumoniae in children: recent insights into the pathogenesis

PURPOSE OF REVIEW

Providing an overview on Mycoplasma pneumoniae-related extra-pulmonary diseases (MpEPDs) in children, who represent the preferred target population by those complications, and discussing the main pathogenic mechanisms implicated or potentially involved.

RECENT FINDINGS

Recent evidences supported the fact that M. pneumoniae is more than an extra-cellular pathogen colonizing epithelial cells of the respiratory tract. It is able to penetrate the cell membrane of host cells and to invade the respiratory mucosa, leading to pronounced inflammatory responses and also spreading outside the respiratory system, to some extent. Thus, direct and indirect (immune-mediated) mechanisms have been described in M. pneumoniae infections, but the latter ones have been mainly implicated in MpEPDs, as reviewed here. Recently, interesting insights have been provided, especially as concern neurologic complications, and new potential mechanisms of disease have been emerging for autoimmunity.

SUMMARY

The awareness of the occurrence of MpEPDs, showing very variable clinical expressions, could promote a correct diagnosis and an appropriate treatment. The knowledge of disease mechanisms in MpEPDs is largely incomplete, but recent advances from clinical studies and murine models might promote and direct future research.

RNA-Seq based transcriptome of whole blood from immunocompetent pigs (Sus scrofa) experimentally infected with Mycoplasma suis strain Illinois

Pigs are popular animal models in biomedical research. RNA-Seq is becoming the predominant tool to investigate transcriptional changes of the pig’s response to infection. The high sensitivity of this tool requires a strict control of the study design beginning with the selection of healthy animals to provide accurate interpretation of research data. Pigs chronically infected with Mycoplasma suis often show no obvious clinical signs, however the infection may affect the validity of animal research. The goal of this study was to investigate whether or not this silent infection is also silent at the host transcriptional level. Therefore, immunocompetent pigs were experimentally infected with M. suis and transcriptional profiles of whole blood, generated by RNA-Seq, were analyzed and compared to non-infected animals. RNA-Seq showed 55 differentially expressed (DE) genes in the M. suis infected pigs. Down-regulation of genes related to innate immunity (tlr8, chemokines, chemokines receptors) and genes containing IFN gamma-activated sequence (gbp1, gbp2, il15, cxcl10, casp1, cd274) suggests a general suppression of the immune response in the infected animals. Sixteen (29.09%) of the DE genes were involved in two protein interaction networks: one involving chemokines, chemokine receptors and interleukin-15 and another involving the complement cascade. Genes related to vascular permeability, blood coagulation, and endothelium integrity were also DE in infected pigs. These findings suggest that M. suis subclinical infection causes significant alterations in blood mRNA levels, which could impact data interpretation of research using pigs. Screening of pigs for M. suis infection before initiating animal studies is strongly recommended.

Tick- and fly-borne bacteria in ungulates: the prevalence of Anaplasma phagocytophilum, haemoplasmas and rickettsiae in water buffalo and deer species in Central Europe, Hungary

Background

Hunting constitutes an important industry in Europe. However, data on the prevalence of vector-borne bacteria in large game animal species are lacking from several countries. Blood or spleen samples (239 and 270, respectively) were taken from red, fallow and roe deer, as well as from water buffaloes, mouflons and wild boars in Hungary, followed by DNA extraction and molecular analyses for Anaplasma phagocytophilum, haemoplasmas and rickettsiae.

Results

Based on blood samples, the prevalence rate of A. phagocytophilum infection was significantly higher in red deer (97.9%) than in fallow deer (72.7%) and roe deer (60%), and in all these compared to mouflons (6.3%). In addition, 39.2% of the spleen samples from wild boars were PCR positive for A. phagocytophilum, but none of the buffalos. Based on blood samples, the prevalence rates of both Mycoplasma wenyonii (Mw) and ‘Candidatus M. haemobos’ (CMh) infections were significantly higher in buffaloes (Mw: 91.2%; CMh: 73.3%) than in red deer (Mw: 64.6%; CMh: 45.8%), and in both of them compared to fallow deer (Mw: 30.3%; CMh: 9.1%) and roe deer (Mw: 20%; CMh: 1.5%). The prevalence of Mw and CMh infection significantly correlated with the body sizes of these hosts. Furthermore, Mw was significantly more prevalent than CMh in buffaloes, red and roe deer. Mycoplasma ovis was detected in mouflons, M. suis in wild boars, R. helvetica in one fallow deer and one mouflon, and an unidentified Rickettsia sp. in a fallow deer.

Conclusions

Forest-dwelling game animal species were found to be important carriers of A. phagocytophilum. In contrast, animals grazing grassland (i.e. buffaloes) were less likely to get infected with this Ixodes ricinus-borne pathogen. Water buffaloes, deer species, mouflons and wild boars harbored haemoplasmas that may affect domestic ungulates. Evaluated animals with larger body size had significantly higher prevalence of infection with haemoplasmas compared to smaller deer species. The above host species rarely carried rickettsiae.

Updating the proteome of the uncultivable hemotrophic Mycoplasma suis in experimentally infected pigs

Mycoplasma suis belongs to the hemotrophic mycoplasmas that are associated with acute and chronic anemia in a wide range of livestock and wild animals. The inability to culture M. suis in vitro has hindered its characterization at the molecular level. Since the publication of M. suis genome sequences in 2011 only one proteome study has been published. Aim of the presented study was to significantly extend the proteome coverage of M. suis strain KI_3806 during acute infection by applying three different protein extraction methods followed by 1D SDS-PAGE and LC-MS/MS. A total of 404 of 795 M. suis KI_3806 proteins (50.8%) were identified. Data analysis revealed the expression of 83.7% of the predicted ORFs with assigned functions but also highlights the expression of 179 of 523 (34.2%) hypothetical proteins with unknown functions. Computational analyses identified expressed membrane-associated hypothetical proteins that might be involved in adhesion or host-pathogen interaction. Furthermore, analyses of the expressed proteins indicated the existence of a hexose-6-phosphate-transporter and an ECF transporter. In conclusion, our proteome study provides a further step toward the elucidation of the unique life cycle of M. suis and the establishment of an in vitro culture. All MS data have been deposited in the ProteomeXchange with identifier PXD002294 (http://proteomecentral.proteomexchange.org/dataset/PXD002294).

A Review of Plasmodium coatneyi-Macaque Models of Severe Malaria

Malaria remains one of the most significant public health concerns in the world today. Approximately half the human population is at risk for infection, with children and pregnant women being most vulnerable. More than 90% of the total human malaria burden, which numbers in excess of 200 million annually, is due to Plasmodium falciparum. Lack of an effective vaccine and a dwindling stockpile of antimalarial drugs due to increased plasmodial resistance underscore the critical need for valid animal models. Plasmodium coatneyi was described in Southeast Asia 50 years ago. This plasmodium of nonhuman primates has been used sporadically as a model for severe malaria, as it mimics many of the pathophysiologic features of human disease. This review covers the reported macroscopic, microscopic, ultrastructural, and molecular pathology of P. coatneyi infection in macaques, specifically focusing on the rhesus macaque, as well as describing the critical needs still outstanding in the validation of this crucial model of human disease.

Biology and Diseases of Swine

Swine are used in biomedical research as models for biomedical research and for teaching. This chapter covers normative biology and behavior along with common and emerging swine diseases. Xenotransplantation is discussed along with similarities and differences of swine immunology.

Pathobiology of Mycoplasma suis

Mycoplasma suis is an uncultivable bacterium lacking a cell wall that attaches to and may invade the red blood cells of pigs. M. suis infections occur worldwide and cause the pig industry serious economic losses due to the disease known as infectious anaemia of pigs or, historically, porcine eperythrozoonosis. Infectious anaemia of pigs is characterised predominantly by acute haemolytic or chronic anaemia, along with non-specific manifestations, such as growth retardation in feeder pigs and poor reproductive performance in sows. The fastidious nature of M. suis, as well as the lack of an in vitro cultivation system, has hampered the understanding of the biology and pathogenicity of this organism. Pathogenetic mechanisms of M. suis include direct destruction of red blood cells by adhesion, invasion, nutrient scavenging, immune-mediated lysis and eryptosis, as well as endothelial targeting. Recently published genome sequences, in combination with proteome analyses, have generated new insights into the pathogenicity of M. suis. The present review combines these data with the knowledge provided by experimental M. suis infections.

Clinical and haematological characterisation of Mycoplasma suis infections in splenectomised and non-splenectomised pigs

Mycoplasma suis causes infectious anaemia in pigs (IAP), which can manifest in various degrees of severity depending on the virulence and the host's susceptibility. As M. suis cannot be cultured in vitro experimental infections of splenectomised animals play an essential role for pathogenesis research. The aim of the present study was to characterise the course of experimental infection using the highly virulent and red blood cell (RBC-) invasive M. suis strain KI3806, to compare the experimental course in splenectomised and non-splenectomised pigs and to correlate clinical and haematological parameters with M. suis blood loads. All infected splenectomised pigs (n=7) were PCR-positive 2 days post infection (DPI) with maximum mean bacterial loads of 1.61 × 10(10)M. suis/mL on 8 DPI. They developed severe anaemia and massive hypoglycaemia by 8 DPI and had to be euthanised preterm (until 8 DPI) without seroconversion. The non-splenectomised pigs (n=7) became PCR-positive within 23 DPI and reached a maximum mean M. suis load of 1.64 × 10(5)M. suis/mL on 8 DPI. They developed mild anaemia, massive skin alterations with petechiae and haemorrhagic diathesis and seroconverted within 35 DPI. The study demonstrated that experimental infection of splenectomised pigs with the highly virulent M. suis strain KI3806 induces a fulminant course of infection. In contrast, M. suis strain KI3806 induces a mild course of disease in non-splenectomised pigs, which resembles the situation in naturally infected pigs. Therefore, these infection models are valuable for future pathogenesis studies on acute and chronic M. suis infections.