Research into AM functionality has been on the rise since AMs are one of the first lines of a defense against invasive pathogens. One of the most prominent fields is investigating liposomes as deliverers of antibiotics for treatment of respiratory intracellular infections. Intracellular parasites, such as M. tuberculosis, C. pneumoniae, L. monocytogenes, L. pneumophila, and F. tularensis, (to name a few) are taken up by AMs via phagocytosis, but are resistant to the biocidal mechanisms of AMs and can survive intracellularly, thus inducing severe respiratory infections. Pulmonary tuberculosis is caused by M. tuberculosis, and is now a major infectious disease worldwide and its incidence is increasing, especially in association with the AIDS pandemic. For sterilization of intracellular parasites in AMs, antibiotics are normally given orally or intravenously, but much of the antibiotics disperse to many different tissues, diminishing its effectiveness. Pulmonary administration of mannosylated liposomes is a much more direct, efficient route in targeting AMs; it enhances antimicrobial effect, reduces the dosage needed, and avoids unnecessary distribution to the blood. Since mannose receptors are exclusively expressed on the surface of AM, mannosylation of liposomes is an appealing approach to cell-selective targeting to AM. The efficacy of pulmonary administration of ciprofloxacin (CPFX) incorporated into mannosylated liposomes (mannosylated CPFX-lipososomes) was examined in rats, and determined to be an efficient means to target AMs.

Host tropism is the infection specificity of certain pathogens to particular hosts and host tissues. This type of tropism explains why most pathogens are only capable of infecting a limited range of host organisms.

Researchers can classify pathogenic organisms by the range of species and cell types that they exhibit host tropism for. For instance, pathogens that are able to infect a wide range of hosts and tissues are said to be amphotropic. Ecotropic pathogens, on the other hand, are only capable of infecting a narrow range of hosts and host tissue. Knowledge of a pathogen's host specificity allows professionals in the research and medical industries to model pathogenesis and develop vaccines, medication, and preventative measures to fight against infection. Methods such as cell engineering, direct engineering and assisted evolution of host-adapted pathogens, and genome-wide genetic screens are currently being used by researchers to better understand the host range of a variety of different pathogenic organisms.

Macrophages (pronunciation: /ˈmakrə(ʊ)feɪdʒ/ | , from Greek "μακρός" ("makrós") = large, "φαγείν" ("phageín") = to eat) are a type of white blood cell that engulfs and digests cellular debris, foreign substances, microbes, cancer cells, and anything else that does not have the types of proteins specific to healthy body cells on its surface in a process called phagocytosis. These large phagocytes are found in essentially all tissues, where they patrol for potential pathogens by amoeboid movement. They take various forms (with various names) throughout the body (e.g., histiocytes, Kupffer cells, alveolar macrophages, microglia, and others), but all are part of the mononuclear phagocyte system. Besides phagocytosis, they play a critical role in nonspecific defense (innate immunity) and also help initiate specific defense mechanisms (adaptive immunity) by recruiting other immune cells such as lymphocytes. For example, they are important as antigen presenters to T cells. In humans, dysfunctional macrophages cause severe diseases such as chronic granulomatous disease that result in frequent infections.

Beyond increasing inflammation and stimulating the immune system, macrophages also play an important anti-inflammatory role and can decrease immune reactions through the release of cytokines. Macrophages that encourage inflammation are called M1 macrophages, whereas those that decrease inflammation and encourage tissue repair are called M2 macrophages. This difference is reflected in their metabolism; M1 macrophages have the unique ability to metabolize arginine to the "killer" molecule nitric oxide, whereas rodent M2 macrophages have the unique ability to metabolize arginine to the "repair" molecule ornithine. However, this dichotomy has been recently questioned as further complexity has been discovered.

Human macrophages are about in diameter and are produced by the differentiation of monocytes in tissues. They can be identified using flow cytometry or immunohistochemical staining by their specific expression of proteins such as CD14, CD40, CD11b, CD64, F4/80 (mice)/EMR1 (human), lysozyme M, MAC-1/MAC-3 and CD68.

Macrophages were first discovered by Élie Metchnikoff, a Russian zoologist, in 1884.

Granulocytopenia is an abnormally low concentration of granulocytes in the blood. This condition reduces the body's resistance to many infections. Closely related terms include agranulocytosis (etymologically, "no granulocytes at all"; clinically, granulocyte levels less than 5% of normal) and neutropenia (deficiency of neutrophil granulocytes). Granulocytes live only one to two days in circulation (four days in spleen or other tissue), so transfusion of granulocytes as a therapeutic strategy would confer a very short-lasting benefit. In addition, there are many complications associated with such a procedure.

There is usually a granulocyte chemotactic defect in individuals suffering from insulin-dependent diabetes mellitus.

Granulocytes are a category of white blood cells characterized by the presence of granules in their cytoplasm. They are also called polymorphonuclear leukocytes (PMN, PML, or PMNL) because of the varying shapes of the nucleus, which is usually lobed into three segments. This distinguishes them from the mononuclear agranulocytes. In common parlance, the term "polymorphonuclear leukocyte" often refers specifically to "neutrophil granulocytes", the most abundant of the granulocytes; the other types (eosinophils, basophils, and mast cells) have lower numbers. Granulocytes are produced via granulopoiesis in the bone marrow.

Neutrophils (also known as neutrocytes) are the most abundant type of granulocytes and the most abundant (40% to 70%) type of white blood cells in most mammals. They form an essential part of the innate immune system. Their functions vary in different animals.

They are formed from stem cells in the bone marrow. They are short-lived and highly motile, or mobile, as they can enter parts of tissue where other cells/molecules cannot. Neutrophils may be subdivided into segmented neutrophils and banded neutrophils (or bands). They form part of the polymorphonuclear cells family (PMNs) together with basophils and eosinophils.

The name "neutrophil" derives from staining characteristics on hematoxylin and eosin (H&E) histological or cytological preparations. Whereas basophilic white blood cells stain dark blue and eosinophilic white blood cells stain bright red, neutrophils stain a neutral pink. Normally, neutrophils contain a nucleus divided into 2–5 lobes.

Neutrophils are a type of phagocyte and are normally found in the bloodstream. During the beginning (acute) phase of inflammation, particularly as a result of bacterial infection, environmental exposure, and some cancers, neutrophils are one of the first-responders of inflammatory cells to migrate towards the site of inflammation. They migrate through the blood vessels, then through tissue, following chemical signals such as Interleukin-8 (IL-8), C5a, fMLP, Leukotriene B4 and HO in a process called chemotaxis. They are the predominant cells in pus, accounting for its whitish/yellowish appearance.

Neutrophils are recruited to the site of injury within minutes following trauma, and are the hallmark of acute inflammation; however, due to some pathogens being indigestible, they can be unable to resolve certain infections without the assistance of other types of immune cells.

Neutrophils display highly directional amoeboid motility in infected footpad and phalanges. Intravital imaging was performed in the footpad path of LysM-eGFP mice 20 minutes after infection with "Listeria monocytogenes".

Monocytes are a type of "leukocyte", or white blood cell. They are the largest type of leukocyte and can differentiate into macrophages and myeloid lineage dendritic cells. As a part of the vertebrate innate immune system monocytes also influence the process of adaptive immunity. There are at least three subclasses of monocytes in human blood based on their phenotypic receptors.

Infection of macrophages in joints is associated with local inflammation during and after the acute phase of "Chikungunya" (caused by CHIKV or Chikungunya virus).

This type of GvHD is associated with transfusion of un-irradiated blood to immunocompromised recipients. It can also occur in situations in which the blood donor is homozygous and the recipient is heterozygous for an HLA haplotype. It is associated with higher mortality (80-90%) due to involvement of bone marrow lymphoid tissue, however the clinical manifestations are similar to GVHD resulting from bone marrow transplantation. Transfusion-associated GvHD is rare in modern medicine. It is almost entirely preventable by controlled irradiation of blood products to inactivate the white blood cells (including lymphocytes) within.

Monocytes are amoeboid in appearance, and have agranulated cytoplasm. Containing unilobar nuclei, these cells are one of the types of mononuclear leukocytes which shelter azurophil granules. The archetypal geometry of the monocyte nucleus is ellipsoidal; metaphorically bean-shaped or kidney-shaped, although the most significant distinction is that the nuclear envelope should not be hyperbolically furcated into lobes. Contrast to this classification occurs in polymorphonuclear leukocytes. Monocytes compose 2% to 10% of all leukocytes in the human body and serve multiple roles in immune function. Such roles include: replenishing resident macrophages under normal conditions; migration within approximately 8–12 hours in response to inflammation signals from sites of infection in the tissues; and differentiation into macrophages or dendritic cells to effect an immune response. In an adult human, half of the monocytes are stored in the spleen. These change into macrophages after entering into appropriate tissue spaces, and can transform into foam cells in endothelium.

An alveolar macrophage (or dust cell) is a type of macrophage found in the pulmonary alveolus, near the pneumocytes, but separated from the wall.

Activity of the alveolar macrophage is relatively high, because they are located at one of the major boundaries between the body and the outside world. They are responsible for removing particles such as dust or microorganisms from the respiratory surfaces.

Alveolar macrophages are frequently seen to contain granules of exogenous material such as particulate carbon that they have picked up from respiratory surfaces. Such black granules may be especially common in smoker's lungs or long-term city dwellers.

Inhaled air may contain particles or organisms which would be pathogenic. The respiratory pathway is a prime site for exposure to pathogens and toxic substances. The respiratory tree, comprising the larynx, trachea, and bronchioles, is lined by ciliated epithelia cells that are continually exposed to harmful matter. When these offensive agents infiltrate the superficial barriers, the body's immune system responds in an orchestrated defense involving a litany of specialized cells which target the threat, neutralize it, and clean up the remnants of the battle.

Deep within the lungs exists its constituent alveoli sacs, the sites responsible for the uptake of oxygen and excretion of carbon dioxide. There are three major alveolar cell types in the alveolar wall (pneumocytes):

- Type I pneumocyte (Squamous Alveolar) cells that form the structure of an alveolar wall.

- Type II pneumocyte (Great Alveolar) cells that secrete pulmonary surfactant to lower the surface tension of water and allows the membrane to separate, thereby increasing the capability to exchange gases. Surfactant is continuously released by exocytosis. It forms an underlying aqueous protein-containing hypophase and an overlying phospholipid film composed primarily of dipalmitoyl phosphatidylcholine.

- Macrophages that destroy foreign material, such as bacteria.

Type 1 and type 2 pneumocytes. Type 1 pneumocytes (or membranous pneumocytes) form the structure of the alveolus and are responsible for the gas exchange in the alveolus. Type 1 pneumocytes are squamous epithelial cells which are characterized by a superficial layer consisting of large, thin, scale-like cells; they also cover 95% of the alveolar surface, although they are only half as numerous as Type 2 pneumocytes. Type 2 pneumocytes are important in that they can proliferate and differentiate into type 1 pneumocytes, which cannot replicate and are susceptible to a vast numbers of toxic insults. Type 2 pneumocytes are also important because they secrete pulmonary surfactant(PS), which consists 80–90% of phospholipids [(phosophatidylcholine(PC), phosphatidyglycerol(PG), phosphaditylinositol (PI)] and 5-10% of surfactant proteins (SP-A, SP-B, SP-C, AND SP-D). PS is synthesized as lamellar bodies, which are structures consisting of closely packed bilayers that are secreted and then undergo transformation into a morphological form called tubular myelin. PS plays an important role in maintaining normal respiratory mechanics by reducing alveolar surface tension. By lowering alveolar surface tension, PS reduces the energy required to inflate the lungs, and reduces the likelihood of alveolar collapse during expiration. Loosely attached to these alveoli sacs are the alveolar macrophages that protect the lungs from a broad array of microbes and aerosols by devouring and ingesting them through phagocytosis.

Alveolar macrophages are phagocytes that play a critical role in homeostasis, host defense, the response to foreign substances, and tissue remodeling. Since alveolar macrophages are pivotal regulators of local immunological homeostasis, their population density is decisive for the many processes of immunity in the lungs. They are highly adaptive components of the innate immune system and can be specifically modified to whatever functions needed depending on their state of differentiation and micro-environmental factors encountered. Alveolar macrophages release numerous secretory products and interact with other cells and molecules through the expression of several surface receptors. Alveolar macrophages are also involved in the phagocytosis of apoptotic and necrotic cells that have undergone cell-death. They must be selective of the material that is phagocytized because normal cells and structures of the body must not be compromised. To combat infection, the phagocytes of the innate immune system facilitates many pattern recognition receptors (PRR) to help recognize pathogen-associated molecular patterns (PAMPs) on the surface of pathogenic microorganisms. PAMPs all have the common features of being unique to a group of pathogens but invariant in their basic structure; and are essential for pathogenicity(ability of an organism to produce an infectious disease in another organism). Proteins involved in microbial pattern recognition include mannose receptor, complement receptors, DC-SIGN, Toll-like receptors(TLRs), the scavenger receptor, CD14, and Mac-1. PRRs can be divided into three classes:

1. signaling PRRs that activate gene transcriptional mechanisms that lead to cellular activation,

2. endocytic PRRs that function in pathogen binding and phagocytosis, and

3. secreted PRRs that usually function as opsonins or activators of complement.

The recognition and clearance of invading microorganisms occurs through both opsonin-dependent and opsonin–independent pathways. The molecular mechanisms facilitating opsonin-dependent phagocytosis are different for specific opsonin/receptor pairs. For example, phagocytosis of IgG-opsonized pathogens occurs through the Fcγ receptors (FcγR), and involves phagocyte extensions around the microbe, resulting in the production of pro-inflammatory mediators. Conversely, complement receptor-mediated pathogen ingestion occurs without observable membrane extensions (particles just sink into the cell) and does not generally results in an inflammatory mediator response.

Following internalization, the microbe is enclosed in a vesicular phagosome which then undergoes fusion with primary or secondary lysosomes, forming a phagolysosome. There are various mechanisms that lead to intracellular killing; there are oxidative processes, and others independent of the oxidative metabolism. The former involves the activation of membrane enzyme systems that lead to a stimulation of oxygen uptake (known as the respiratory burst), and its reduction to reactive oxygen intermediates (ROIs), molecular species that are highly toxic for microorganisms. The enzyme responsible for the elicitation of the respiratory burst is known as nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, which is composed of five subunits. One component is a membrane cytochrome made up of two protein subunits, gp91phox and p22phox; the remaining three components are cytosolic-derived proteins: p40phox, p47phox, and p67phox. NADPH oxidase exists in the cytosol of the AM when in a quiescent state; but upon activation, two of its cytosolic components, p47phox and p67phox, have their tyrosine and serine residues phosphorylated, which are then able to mediate translocation of NADPHox to the cytochrome component, gp91phox/p22phox, on the plasma membrane via cytoskeletal elements.

Compared to other phagocytes, the respiratory burst in AM is of a greater magnitude. Oxygen-independent microbicidal mechanisms are based on the production of acid, on the secretion of lysozymes, on iron-binding proteins, and on the synthesis of toxic cationic polypeptides. Macrophages possess a repertoire of antimicrobial molecules packaged within their granules and lysosomes. These organelles contain a plethora of degradative enzymes and antimicrobial peptides that are released into the phagolysosome, such as proteases, nucleases, phosphatases, esterases, lipases, and highly basic peptides. Moreover, macrophages possess a number of nutrient deprivation mechanisms that are used to starve phagocytosed pathogens of essential micronutrients. Certain microorganisms have evolved countermeasures which enable them to evade being destroyed by phagocytes. Although lysosomal-mediated degradation is an efficient means by which to neutralize an infection and prevent colonization, several pathogens parasitize macrophages, exploiting them as a host cell for growth, maintenance and replication. Parasites like Toxoplasma gondii and mycobacteria are able to prevent fusion of phagosomes with lysosomes, thus escaping the harmful action of lysosomal hydrolases. Others avoid lysosomes by leaving the phagocytic vacuole, to reach the cytosolic matrix where their development is unhindered. In these instances, macrophages may be triggered to actively destroy phagocytosed microorganisms by producing a number of highly toxic molecules and inducing deprivational mechanism to starve it. Finally, some microbes have enzymes to detoxify oxygen metabolites formed during the respiratory burst.

When insufficient to ward off the threat, alveolar macrophages can release proinflammatory cytokines and chemokines to call forth a highly developed network of defensive phagocytic cells responsible for the adaptive immune response.

The lungs are especially sensitive and prone to damage, thus to avoid collateral damage to type 1 and type II pneumocytes, alveolar macrophages are kept in a quiescent state, producing little inflammatory cytokines and displaying little phagocytic activity, as evidenced by downregulated expression of the phagocytic receptor Macrophage 1 antigen (Mac-1). AMs actively suppress the induction of two of the immunity systems of the body: the adaptive immunity and humoral immunity. The adaptive immunity is suppressed through AM’s effects on interstitial dendritic cells, B-cells and T-cells, as these cells are less selective of what they destroy, and often cause unnecessary damage to normal cells. To prevent uncontrolled inflammation in the lower respiratory tract, alveolar macrophages secrete nitric oxide, prostaglandins, interleukin-4 and -10(IL-4, IL-10), and transforming growth factor-β (TGF-β).

There are a large number of clinical trials either ongoing or recently completed in the investigation of graft-versus-host disease treatment and prevention. Currently, there are no reliable molecular markers reflecting the onset or clinical course of aGVHD. However, it has been shown that genes responsible for cytokine signaling, inflammatory response, and regulation of cell cycle are differentially expressed in patinets with fatal GvHD versus „indolent“ GvHD.

On May 17, 2012, Osiris Therapeutics announced that Canadian health regulators approved Prochymal, its drug for acute graft-versus host disease in children who have failed to respond to steroid treatment. Prochymal is the first stem cell drug to be approved for a systemic disease.

In January 2016, Mesoblast released results of a Phase2 clinical trial on 241 children with acute Graft-versus-host disease, that was not responsive to steroids. The trial was of a mesenchymal stem cell therapy known as remestemcel-L or MSC-100-IV. Survival rate was 82% (vs 39% of controls) for those who showed some improvement after 1 month, and in the long term 72% (vs 18% of controls) for those that showed little effect after 1 month.

A pathogen will display tropism for a specific host if it can interact with the host cells in a way that supports pathogenic growth and infection. Various factors affect the ability of a pathogen to infect a particular cell, including: the structure of the cell's surface receptors; the availability of transcription factors that can identify pathogenic DNA or RNA; the ability of the cells and tissue to support viral or bacterial replication; and the presence of physical or chemical barriers within the cells and throughout the surrounding tissue.

Gamma delta T cells (γδ T cells) are T cells that have a distinctive T-cell receptor (TCR) on their surface. Most T cells are αβ (alpha beta) T cells with TCR composed of two glycoprotein chains called α (alpha) and β (beta) TCR chains. In contrast, gamma delta (γδ) T cells have a TCR that is made up of one γ (gamma) chain and one δ (delta) chain. This group of T cells is usually much less common than αβ T cells, but are at their highest abundance in the gut mucosa, within a population of lymphocytes known as intraepithelial lymphocytes (IELs).

The antigenic molecules that activate gamma delta T cells are still largely unknown. However, γδ T cells are peculiar in that they do not seem to require antigen processing and major-histocompatibility-complex (MHC) presentation of peptide epitopes, although some recognize MHC class Ib molecules. Furthermore, γδ T cells are believed to have a prominent role in recognition of lipid antigens. They are of an invariant nature and may be triggered by alarm signals, such as heat shock proteins (HSP).

There also exists a γδ-T-cell sub-population within the epidermal compartment of the skin of mice. Originally referred to as Thy-1+ dendritic epidermal cells (Thy1+DEC), these cells are more commonly known as dendritic epidermal T cells (DETC). DETCs arise during fetal development and express an invariant and canonical Vγ3 Vδ1 T-cell receptor [using Garman nomenclature].

The T helper cells (T cells) are a type of T cell that play an important role in the immune system, particularly in the adaptive immune system. They help the activity of other immune cells by releasing T cell cytokines. These cells help suppress or regulate immune responses. They are essential in B cell antibody class switching, in the activation and growth of cytotoxic T cells, and in maximizing bactericidal activity of phagocytes such as macrophages.

Mature T cells express the surface protein CD4 and are referred to as CD4 T cells. Such CD4 T cells are generally treated as having a pre-defined role as helper T cells within the immune system. For example, when an antigen-presenting cell expresses an antigen on MHC class II, a CD4 cell will aid those cells through a combination of cell to cell interactions (e.g. CD40 (protein) and CD40L) and through cytokines.

CD154, also called CD40 ligand or CD40L, is a cell surface protein that mediates T cell helper function in a contact-dependent process and is a member of the TNF superfamily of molecules. It binds to CD40 on antigen-presenting cells (APC), which leads to many effects depending on the target cell type. CD154 acts as a costimulatory molecule and is particularly important on a subset of T cells called T follicular helper cells (T cells). On T cells, CD154 promotes B cell maturation and function by engaging CD40 on the B cell surface and therefore facilitating cell-cell communication. A defect in this gene results in an inability to undergo immunoglobulin class switching and is associated with hyper IgM syndrome. Absence of CD154 also stops the formation of germinal centers and therefore prohibiting antibody affinity maturation, an important process in the adaptive immune system.

The importance of helper T cells can be seen from HIV, a virus that primarily infects CD4 T cells. In the advanced stages of HIV infection, loss of functional CD4 T cells leads to the symptomatic stage of infection known as the acquired immunodeficiency syndrome (AIDS). When the HIV virus is detected early in blood or other bodily fluids, continuous therapy can delay the time at which this fall happens. Therapy can also better manage the course of AIDS if and when it occurs. There are other rare disorders such as lymphocytopenia which result in the absence or dysfunction of CD4 T cells. These disorders produce similar symptoms, many of which are fatal.

The preventative measure of keeping cats inside in areas with high infection rates can prevent infection. Approved tick treatments for cats can be used but have been shown not to fully prevent tick bites.

The most often used treatments for cytauxzoonosis are imidocarb dipropionate and a combination of atovaquone and azithromycin. Although imidocarb has been used for years, it is not particularly effective. In a large study, only 25% of cats treated with this drug and supportive care survived. 60% of sick cats treated with supportive care and the combination of the anti-malarial drug atovaquone and the antibiotic azithromycin survived infection.

Quick referral to a veterinarian equipped to treat the disease may be beneficial. All infected cats require supportive care, including careful fluids, nutritional support, treatment for complications, and often blood transfusion.

Cats that survive the infection should be kept indoors as they can be persistent carriers after surviving infection and might indirectly infect other cats after being themselves bitten by a vector tick.

Currently, there is no vaccine against human granulocytic anaplasmosis, so antibiotics are the only form of treatment. The best way to prevent HGA is to prevent getting tick bites.

Yersiniosis is usually self-limiting and does not require treatment. For severe infections (sepsis, focal infection) especially if associated with immunosuppression, the recommended regimen includes doxycycline in combination with an aminoglycoside. Other antibiotics active against "Y. enterocolitica" include trimethoprim-sulfamethoxasole, fluoroquinolones, ceftriaxone, and chloramphenicol. "Y. enterocolitica" is usually resistant to penicillin G, ampicillin, and cephalotin due to beta-lactamase production.

Yersinia pseudotuberculosis is a Gram-negative bacterium that causes Far East scarlet-like fever in humans, who occasionally get infected zoonotically, most often through the food-borne route. Animals are also infected by "Y. pseudotuberculosis". The bacterium is urease positive.

Because "B. suis" is facultative and intracellular, and is able to adapt to environmental conditions in the macrophage, treatment failure and relapse rates are high. The only effective way to control and eradicate zoonosis is by vaccination of all susceptible hosts and elmination of infected animals. The "Brucella abortus" (rough LPS "Brucella") vaccine, developed for bovine brucellosis and licensed by the USDA Animal Plant Health Inspection Service, has shown protection for some swine and is also effective against "B. suis" infection, but currently no approved vaccine for swine brucellosis is available.

In animals, "Y. pseudotuberculosis" can cause tuberculosis-like symptoms, including localized tissue necrosis and granulomas in the spleen, liver, and lymph nodes.

In humans, symptoms of Far East scarlet-like fever are similar to those of infection with "Yersinia enterocolitica" (fever and right-sided abdominal pain), except that the diarrheal component is often absent, which sometimes makes the resulting condition difficult to diagnose. "Y. pseudotuberculosis" infections can mimic appendicitis, especially in children and younger adults, and, in rare cases, the disease may cause skin complaints (erythema nodosum), joint stiffness and pain (reactive arthritis), or spread of bacteria to the blood (bacteremia).

Far East scarlet-like fever usually becomes apparent five to 10 days after exposure and typically lasts one to three weeks without treatment. In complex cases or those involving immunocompromised patients, antibiotics may be necessary for resolution; ampicillin, aminoglycosides, tetracycline, chloramphenicol, or a cephalosporin may all be effective.

The recently described syndrome "Izumi-fever" has been linked to infection with "Y. pseudotuberculosis".

The symptoms of fever and abdominal pain mimicking appendicitis (actually from mesenteric lymphadenitis) associated with "Y. pseudotuberculosis" infection are not typical of the diarrhea and vomiting from classical food poisoning incidents. Although "Y. pseudotuberculosis" is usually only able to colonize hosts by peripheral routes and cause serious disease in immunocompromised individuals, if this bacterium gains access to the blood stream, it has an LD comparable to "Y. pestis" at only 10 CFU.

Evidence in support of the idea that helminthic infections reduce the severity of autoimmune diseases is primarily derived from animal models. Studies conducted on mice and rat models of colitis, muscular sclerosis, type 1 diabetes, and asthma have shown helminth-infected subjects to display protection from the disease. While helminths are often considered a homogenous group, considerable differences exist between species and the utilization of species in clinical research varies between human and animal trials. As such, caution must be exercised when interpreting the results from animal models.

Helminthic therapy is currently being studied as a treatment for several (non-viral) autoimmune diseases in humans including celiac disease, Crohn's disease, multiple sclerosis, ulcerative colitis, and atherosclerosis. It is currently unknown which clinical dose or species of helminth is the most effective method of treatment. Hookworms have been linked to reduced risk of developing asthma, while "Ascaris lumbricoides" (roundworm infection) was associated with an "increased" risk of asthma. Similarly, "Hymenolepis nana", "Trichoris trichiura", "Ascaris lumbricoides", "Strongyloides stercolaris", "Enterobius vermicularis", and "Trichuris suis" ova have all been found to lower the number of symptom exacerbations, reduce the number of symptom relapses, and decrease the number of new or enlarging brain lesions in patients with multiple sclerosis at doses ranging from 1,180 to 9,340 eggs per gram. However, "Ascaris lumbricoides", "Strongyloides stercolaris" and "Enterobius vermicularis" are not considered suitable for therapeutic use in humans because they do not meet the criteria for a therapeutic helminth.

"Trichuris suis" ova has been used in most cases to treat autoimmune disorders because it is thought to be non-pathogenic in humans and therefore has been rendered as safe.

The use of "Trichuris suis" ova has been granted by the USA Food and Drug Administration as an investigational medicinal product (IMP). While in the UK, the hookworm "Necator americanus" has been granted an IMP license by the Medicines and Healthcare Regulatory Authority. This hookworm is likely to be relatively safe, although it can cause temporary gastrointestinal side effects, especially following the initial inoculation and with larger doses.

The general ideal characteristics for a therapeutic helminth are as follows:

- Little or no pathogenic potential

- Does not multiply in the host

- Cannot be directly spread to close contacts

- Produces a self-limited colonization in humans

- Produces an asymptomatic colonization in humans

- Does not alter behaviour in patients with depressed immunity

- Is not affected by most commonly used medications

- Can be eradicated with an anti-helminthic drug

- Can be isolated free of other potential pathogens

- Can be isolated or produced in large numbers

- Can be made stable for transport and storage

- Easy to administer

Fumagillin has been used in the treatment.

Another agent used is albendazole.

The primary method for controlling the incidence of gaffkaemia is improved hygiene. Other measures include limiting damage to the exoskeleton (preventing the bacterium's entry), reducing the water temperature, and reducing the stocking density. Antibiotics may be effective against the bacterium, but only tetracycline is currently approved by the U.S Food and Drug Administration for use in American lobsters.