Dynamics of leptospirosis in domestic animals

Leptospirosis

M.C.V. Ramón Alfredo Delgado González

División Regional de Ciencia Animal

Universidad Autónoma Agraria Antonio Narro, Unidad Laguna

History

The first report of leptospirosis was carried out in 1886 in Germany by Dr. Adolf Weil, who reported in humans a febrile illness with jaundice associated with a disorder that affects the kidneys, liver, and spleen. In 1887, a similar disease was described by Goldschmidt, who registered as ‚Äúsyndrome of Weil‚ÄĚ. The morphology of Leptospira, described in 1907 as an ‚Äúagent in a spiral with ends in hook form‚ÄĚ appointed as¬†Spirochaeta interrogans, however, Dr. Hideyo Noguchi, in 1917, described it within a new genre calling ‚ÄúLeptospira ‚Äú. In M√©xico, the first cases of leptospirosis were reported in 1920, in humans, in Merida, Yucat√°n. However, it was not until the decade of the 30‚Äôs that began to report cases in animals, being in 1953, the first report of leptospirosis in cattle in M√©xico.

Fundamentals

Leptospirosis is a zoonotic bacterial disease of worldwide distribution, is endemic in tropical and temperate climates. Affects the majority of the pets and is reported in reptiles, birds, amphibians and arthropods. It is considered an emerging infectious disease in humans, and therefore of great importance in public health.

Leptospira belongs to the family of the phylum¬†Spirochaete Leptospiraceae. Leptospira are thin mobile spirochetes, with one end in the form of a hook, aerobic and of slow growth that has an optimal development to 30 ¬įC. The agency is extremely sensitive to pH extremes, lack of humidity and soft disinfectants including the detergent. There are saprophytes and pathogenic species in nature. The saprophytes species live in water and soil and do not infect animals.

Taxonomy

The Leptospira genus includes, 19 species geneticallyidentified, and there are around 260 pathogenic serovarietys, according to the patterns of surface antigens, and are combined in 24 serogroups. There is no correlation between the serological and genetic classifications.

The genus is quite heterogeneous, is classified according to their genetic characteristics and is divided into three groups; pathogenic, non-pathogenic, and possibly opportunistic pathogens. The pathogenic leptospira includes eight genospecies:¬†Leptospira interrogans,¬†Leptospira borgpetersenii,¬†Leptospira kirschneri,¬†Leptospira santarosai,¬†Leptospira weilii,¬†Leptospira alexanderi,¬†Leptospira noguchii¬†and¬†Leptospira alstonii¬†(Brenner and col., 1999). The group of saprophytes species includes six free-living microorganisms that are found on the surface of waters as¬†Leptospira biflexa,¬†Leptospira wolbachii, Leptospira kmetyi,¬†Leptospira yanagawae, Leptospira terpstrae and Leptospira vanthielii. Another group includes species of ‚Äúintermediate behavior‚ÄĚ, whose role in its pathogenicity has not been demonstrated:¬†Leptospira inadai, Leptospira broomii, Leptospira fainei, Leptospira wolfii and Leptospira licerasiae.

Pathogenesis

The sources of Leptospires are essentially domestic and wild mammals that house the spirochetes in the proximal tubules outlined the kidneys and deleted intermittently leptospires in large numbers (106 /mL) through the urine toward the environment, around the seventh-day post-infection. Therefore, the urine of infected animals presents a potential source of infection.

Leptospirosis has an incubation period of 3 to 20 days, variable according to the virulence and amount of microorganisms and the physiological state and immune systems of the host. To survive in the environment, the bacterium needs to be able to detect and move toward favorable conditions and far from unfavorable conditions. The chemotaxis and motility allow the bacterium to penetrate the barriers of the tissues of the host during the infection; it is based on a directional movement toward an attractive or away from a repellent. The adaptation to various environmental stimuli outside and inside the guest and the ability to survive in the bloodstream contributes to the Leptospira can cause disease, when migrating through the intercellular spaces.

Leptospires enter the body through mucous membranes of the eyes, nose or throat and through cuts or abrasions in the skin, and invade the tissues and fluids of the host. After the contact, the spirochetes spread through the bloodstream and move toward the hemoglobin, movement that is related to its virulence, to multiply in the target organs such as the kidneys, liver, lungs, and uterus resulting in a broad spectrum of clinical manifestations. The septicemic phase or leptospiremia is characterized by the appearance of antibodies and leptospira in blood.

Leptospires penetrate the skin rapidly eroded and establish a systemic infection to cross the barriers of the tissues. Leptospires can move through the barrier of the tissues by association with the blood vessels since the leptospira are detected added around the capillaries in the muscle layer, and spread through the intercellular junctions and can also be detected in the cytoplasm of the endothelial cells of the host.

When penetrating, the leptospira are found in blood at 2 post-infection hours (p.i.h.), which are increasing between 8 and 96 p.i.h. reaching its peak and begin to decline at 144 p.i.h. Leptospires are detected encapsulated by vascular endothelial cells, which swell, causing damage to the vascular basement membrane and often added around the capillaries in the dermis and subcutaneous tissue under the site of infection. Bleeding can be found in the dermis around the site of infection before the appearance of hemorrhages in internal organs. The layer of keratinocytes intact is a very efficient barrier that can prevent the infiltration of leptospires to the host. In the muscle layers, leptospires are detected added around the capillaries to 24 p.i.h., which are frequently devoured by neutrophils and macrophages. After spread to the liver, lungs, kidneys, uterus, mammary gland and other tissues, almost all animals within the 96 p.i.h.  In the liver leptospires are found in the membranes of the hepatocytes, also as a granular tank in Kupffer cells after 24 p.i.h. The lungs may show leptospires in the pockets of hemorrhage and rarely around or outside of them. In the kidneys, a large number of leptospires are typically viewed in the glomerular spaces (96 p.i.h.). You can find leptospires aligned surrounding the peritoneal capillaries 72 p.i.h.

The adherence to the cells and components of the extracellular matrix (ECM) the guest is probably a necessary step for the leptospira penetrate, spread and persist in the tissues of the mammalian hosts. You have found a wide range of adhesion molecules in leptospires that give the ability to migrate through the tissues; many leptospiral proteins have an affinity for the ECM and surfaces of the cells.

The animals infected by leptospira, track the conjunctiva and injured by skin, develop clinical signs and pathological changes similar. The pathogenic leptospira is able to survive and be more resistant to the action of the immune system.

Leptospires are not necessary intracellular parasites but can be entered in cells and reside in these temporarily, in phagocytic cells, not normal microorganisms enter and are in phagosomes in the cytoplasm. To use this mechanism of entry into the cell, allows the Leptospira spread to target organs, to evade the immune response, the microorganism seems to survive unless they are present specific antibodies.

To get to the liver or kidneys infectious strains of Leptospira adhere  to components of the ECM between the interstices of the hepatocytes and tubular epithelial cells, such as collagen type I, type IV,  laminin, and fibronectin. Due to the epithelial cells of the proximal tubules of the kidney produce proteoglycans, they can facilitate the colonization of the kidney, especially in animal’s guests.

During the leptospiremia, the migration of the Leptospira to the uterus and oviduct of animals not pregnant, and the placenta in the pregnant female produce capillary congestion, and endothelial cells and effects of necrobiotic vacuolated and apoptosis, besides are observed leptospires in endothelial cells. These damages are capable of producing early embryo death and abortion in all stages of pregnancy and the Leptospira can be found in the kidneys, adrenal, and liver of aborted fetuses. The inflammation that may occur at the level of cotyledons brings as a consequence retained placenta, in addition to that may cause infertility, sterility and even in extreme cases.

Signs, Symptoms and lesions

The clinical signs of leptospirosis are directly influenced by the virulence of the infecting serotype, the dose of the inoculums, age, susceptibility and physical condition of the animals. The acute infection may be potentially lethal or in hosts of maintenance can cause a chronic illness with little clinic symptomatology; most infections result in slight disease with nonspecific signs such as fever and muscle weakness. The clinical picture of a severe leptospirosis is characterized by liver dysfunction, renal and hemorrhages. Occasionally you can see blood in the urine, hemoglobinuria, decay, anorexia and death in a few hours. The animals usually die of septic shock with organ failure.

In the leptospiral infection dead animals can display the necropsy hepatomegaly, splenomegaly, and jaundice in the mucous membranes and subcutaneous tissue, and petechial bleeding scattered in almost all organs and tissues. In the severe form, there are hemodynamic alterations and hypovolemia due to dehydration and the direct effect of the toxins that damage the vascular endothelium and increase the permeability. Several factors are involved in the acute renal damage in the leptospirosis, including the direct nephrotoxic action of leptospires, hyperbilirubinemia, rhabdomyolysis, and hypovolemia. The anomalies in the tubular function precede a decrease in the glomerular filtration rate, which could explain the high frequency of hypokalemia.

The hemorrhages were characterized by petechiae and bruises coalescing, scattered in the skin until the subcutaneous tissue and muscle that progress with the time. Later you can develop petechial bleeding in the lungs. In the liver are appreciated hemorrhage, edema, and necrotic foci. The kidneys also show extensive hemorrhages in the peritoneal surface. In addition, the tubular epithelial cells are necrosis and infiltration of erythrocytes in his light, presenting hematuria after.

Epidemiology

Leptospires that cause disease can be classified as 1) adapted to the host, which infect animals hosts in maintenance, 2) not adapted to the host, which infect animals accidental hosts . The various serotypes are adapted to different animal host’s reservoir, wild or domestic and recognition of these serovars has epidemiological importance. The animals can serve as reservoirs of some serovars and become the incidental host of others.

Many species of animals, domestic and wild, serve as hosts reservoirs (carriers), resulting in a global dissemination of the disease, probably the wild reservoirs are the hosts in the maintenance of the majority of the pathogenic leptospira. Humans are incidental hosts. Humans and animals can become infected by direct contact with body fluids of animals that are eliminating the leptospira in the urine, uterine secretions, and milk by tissues of infected animals, after the ingestion of food and water and the inhalation of drops in aerosol contaminated by urine, or indirectly through the presentation of wet soil, water and vegetation. The pathogenic Leptospira can survive for long periods of time in the environment.

Leptospirosis in cattle

In the cattle, leptospirosis causes economic losses of a primary way by its effects on reproduction, may appear early embryo death, stillbirths, abortions, and/or birth of weak animals that may die in the first few days of life and infertility. Secondarily, there may also be economic losses as a result of the ‚Äúsyndrome of the fall of the milk‚ÄĚ or transitory agalactia.

In addition, leptospirosis can pursue with different clinical pictures, which can go from an acute/hyperacute with fever, hematuria, hemoglobinuria, meningitis, and even death to a chronic box whose only symptomatology apparent is the reproductive failure.

Cattle are guests of maintenance of L. borgpetersenii serovar hardjo-bovis, and infected animals typically do not show apparent signs of the infection, except during the gestation. The reproductive failures (abortions, stillbirths, and the birth of weak offspring) and reduced production of milk due to infection by the serovar Hairdo have a significant impact on the industry of meat and milk. In addition, as a human pathogen, the serovar Hardjo is a threat to the health of workers in the animal industry.

Leptospira borgpetersenii serovar hardjo-bovis¬†is the most common cause of abortion and infertility in cattle from North America. Hardjo is a serovar adapted to the cattle, which become chronic carriers and act as reservoirs of infection.¬†L. interrogans serovars Pomona, Icterohaemorrhagiae and Grippotyphosa¬†are leptospires not adapted to the cattle but the infected as hosts accidental, causing acute disease and abortion. Other bacteria associated with abortion in cattle are the¬†Hebdomadis serogroups, serotype sejroe. The dogs are carriers of the main serovars of leptospira affecting cattle ‚ÄstHairdo, Pomona, Grippotyphosa, Icterohaemorrhagiae and Canicola¬†-; the latter also causes disorders in cattle.

Leptospirosis in dogs.Leptospirosis is considered an emerging infectious disease in humans, and therefore of great importance in public health. Leptospirosis has spread throughout the world in stray dogs. The most frequent serovars associated with canine leptospirosis are Canicola, Pomona, Grippotyphosa, Bratislava and Icterohaemorrhagiae, although have been reported infections with other serovars with acute renal failure, in dogs of North America. The dogs are associated to the serovar canicola as hosts of maintenance, whereas rats are reservoirs of the serovar icterohaemorrhagiae. Leptospirosis in dogs is recognized as a risk factor for the human. The increase of rainfall is associated with the prevalence of leptospirosis in dogs. An infected dog can be an asymptomatic carrier of leptospira and shed microorganisms through the urine for its entire life. The macroscopic lesions may show hepatomegaly, splenomegaly, and jaundice in the mucous membranes and subcutaneous tissue, and petechial bleeding scattered in almost all organs and tissues. The histological findings show diffuse inflammatory infiltrates and leptospires are found in many organs, including lung, liver, and kidneys. In the kidneys are detected areas of necrosis with cortical marked interstitial edema, glomerulitis, interstitial nephritis with infiltration of neutrophils, lymphocytes, monocytes, plasma cells and occasionally infarctions, the tubulointerstitial nephritis and acute tubular necrosis are the most common histological finding, but you can develop a tubulointerstitial fibrosis.

In¬†strays¬†dogs from Mexico have been observed approximately 67.5% of positive sera by MA, and 21.0 percent of suspects to the serovars canicola and Portland ‚Äď vere both with a percentage of 60.4%, followed by Bratislava (39.5%), Palo Alto strain (32.5%), Pyrogenes (30.2%), icterohaemorrhagiae (25.5%), Grippotyphosa (6.9%), Pomona (6.9%), and INIFAP strain (4.6%).

In Brazil studies with MA show a prevalence of leptospirosis in the entire country of 26%, being the most prevalent serotypes Autumnalis (34.2%), Tarassovi (23.7%), canicola (17.1%), Grippotyphosa (14.5%) and others with lower prevalence as Bratislava (3.9%), icterohaemorrhagiae (2.7%), Australis, Pomona and wolffi with (1.3%) (Castro and col., 2011). In Buenos Aires, Argentina a seropositivity was found in 57% of dogs examined; 82% of the seropositive agglutination with two or more serotypes. The most frequently detected serotypes were canicola and pyrogenes. In the United States and Canada have been documented studies that show to Leptospira serovar Autumnalis, Grippotyphosa, and Pomona as the main serovars in dogs. Of these, the serovars found in our country are Canicola, Grippotyphosa, Bratislava, Icterohaemorrhagiae, and Pomona, but there are also other serovars of national isolates not notified in studies in other countries as the strains portland-vere, INIFAP and Palo Alto. The dogs are considered the hosts for maintenance to the serovar Canicola and incidental host for other serovars and are a potential source of infection for the pet owners.

Leptospirosis in horses. Leptospirosis is a zoonotic infectious disease of worldwide distribution that affects humans, domestic animals and wildlife, including the horses. The infection is often by a direct drive with urine-contaminated or liquids of placentas, or indirectly by a polluted environment. The clinical manifestations of leptospirosis vary from acute, subacute to chronic infection. The severe disease includes jaundice, hemoglobinuria, kidney failure, meningitis, and abortion, in all pets. The subclinical forms may be more common with animals chronically infected patients, which may be carriers for its entire life.

The main disorders reported in horses are the uveitis, abortion, foals born weak, foals premature, renal dysfunction and liver dysfunction. The observed signs include hematuria, fever, jaundice, anorexia and respiratory disorders.

Serological evidence of infection by Leptospira in horses must be predominantly to the serovars of L. interrogans sv Pomona, L. interrogans sv Bratislava, L. interrogans sv icterohaemorrhagiae and L. kirschneri sv Grippotyphosa.

In horses of Mexico have reported frequencies of serovars  in  three equestrian centers that include L. pyrogenes ( 100%), L. canicola (96%), L. jez Bratislava (56.5%, 61.1%, and 80.6%), L. pryrogenes (61.1% and 72.2%), L. autunmalis (66.7%).

Diagnosis.The majority of the cases of leptospirosis were diagnosed by serology to detect antibodies, due to the cultivation of Leptospires from biological fluids (blood, cerebrospinal fluid, urine, milk) takes several weeks, in addition, to be expensive. The microscopic agglutination test (AM), known as the gold test , is the technique of reference more used, despite the fact that it has been found that the rate of false negative results is 13%. The AM is based on the evaluation of samples of matched sera and has the ability to agglutinate strains of serovars of reference with a battery of live antigens of Leptospira.

The test of AM e s highly specific, but its low sensitivity (30-60%) makes it inappropriate for the diagnosis of acute leptospirosis. Other serological tests as indirect hemagglutination, agglutination in microcapsule and latex agglutination, and ELISA do not offer satisfactory levels of sensitivity and specificity for the diagnosis in an early stage of leptospirosis in the detection of IgM antibodies. The test of the polymerase chain reaction is early and sensitive, but their high cost and the need to have a good quality control are the major drawbacks for your application.

The antigen of Leptospira interrogans Hardjo-prajitno is very sensitive for the detection of antibodies Hardjo in the test of AM, since it detects the 98.4% of the positive sera to Hardjo-prajitno, compared with the 1.6% that detects the antigen of Leptospira borgpetersenii Hardjo-bovis.

There are several potential problems associated with the maintenance of the reference strains of Leptospira; the contamination of strains with other bacteria or saprophytic leptospira of rapid growth, the incorrect labeling or the change of strains. Contamination by other bacteria is easily recognized but the change of strains is a serious error. In addition, if there is no adequate quality control to be carried out on the reference strains, these problems may not be identified in a timely manner. This could adversely affect the investigation of outbreaks and epidemiological studies.

Prophylaxis and treatment. The immunity to the Leptospira is serogroup specific, and the knowledge of the serogroups, that commonly cause disease in a particular geographical region, it is important for the development of vaccines.

Some monovalent vaccines commercially serovar Hardjo induce proliferation of CD4 + T cells and production of gamma interferon (IFN-γ) in response to an antigen of the serovar. The induction of this response seems to provide short-term (4 months) the protective immunity against urinary elimination or a kidney infection after exposure in vivo. These vaccines reduce renal colonization and urinary elimination of bacteria, however, no vaccine provides immunity sterile since it is possible to detect antigen in the majority of animals vaccinated with PCR techniques.

The treatments that are in the present act on the leptospira are doxycycline, amoxicillin, ampicillin, erythromycin, azytromicin, fluoroquinolone, cephalosporins.