Immunohistochemical diagnosis of infectious diseases
In general, diagnosis of infectious diseases depends on microbiological, parasitological, virological and molecularbiological methods. Material for these investigations derives directly from the animal (e.g. swabs, faeces, organ samples). Furthermore, infectious agents may be identified during pathological investigations in formalinfixed paraffin embedded material (virus inclusion bodies, bacteria, fungi). They can be detected by special staining methods in the slides ( e.g. PAS-reaction, silver stains, giemsa). Additionally, immunohistochemical methods are used to identify infectious agents within the tissue.
Immunohistochemistry uses specific antibodies to detect the antigen (virus, tumour marker) in the tissue and to label this binding site by brown staining reaction. Immunohistochemical methods can be applied subsequently to the histological investigations on the submitted material. This is of special interest in material submitted from dead animals where danger of infection for other animals is suspected (e.g. Parvovirus, FIP). Immunohistochemical methods for detection of some important infectious agents in dogs and cats are available in our laboratory.
Feline Infectious Peritonitis (FIP)
FIP is induced by a coronavirus, mostly affecting young or older immunodeficient cats. Two different types of the disease can be distinguished: The humid type of FIP disease appears if the animal develops humoral immunoreaction only. It is characterized by amber fluid in abdomen or thorax which is positive in Rivalta testing. Serologically a hypergamma-globulinaemia is seen. The granulomatous type of FIP disease is seen in cats who develop humoral and cellular immunoreaction. This type is characterized by perivascular white granulomas on the serosa of the gut and within the kidneys. Typically, pyogranulomatous lymphadenitis of the mesenterial lymphnodes can be found which is often misinterpreted as a lymphoma.
Perivascular granulomas in the kidney of a cat with FIP
granulomatous lymphadenitis in a cat with FIP
FIP-virus antigen is detected immunohistochemically within the center of the lesions - thus other infectious diseases can be excluded
Feline Herpesvirus type 1 may lead to systemic or respiratory diseases. Commonly young cats or older animals suffering from immunodeficiency are affected. Persistent infection and recurrent virus excretion may occur. In the lungs an acute necrotizing – purulent bronchopneumonia is seen, probably leading to death. The virus can be identified by PCR or by immunohistochemical methods in the tissue.
FIP-virus antigen is detected immunohistochemically within the center of the lesions - thus other infectious diseases can be excluded.
Feline Leukaemia Virus (FeLV)
Feline Leukaemia Virus is a retrovirus type C, commonly leading to immunodeficiency, anaemia, hepatic lipidosis and enteritis. Neoplasms (lymphoma, sarcoma due to FeSV) develop in only about 30% of the cases. Lymphoma of the thymus is induced by FeLV in most cases, but intestinal and renal lymphomas are rarely caused by FeLV. Vaccination against FeLV has changed the epidemiological data in Germany markedly and the disease is less common today. In numerous cases the diagnosis is made serologically. However, the virus may be detected immunohistochemically within tissue samples.
Feline Panleukopenia / Canine Parvovirus
Two different parvoviruses are the cause of feline panleukaemia and canine parvovirus enteritis. In most cases young animals or those with an incomplete vaccination status are affected. The virus affects lymphatic tissues (bone marrow, spleen, lymph nodes) and epithelia of the gastro-intestinal tract. Clinical symptoms of vomiting and diarrhoea may complicated by bacterial infections. In faeces the diagnosis may be done by commercially available quick-tests.
Grossly a smooth mucosa with villus atrophy and edema of the intestinal wall as well as watery ingesta are typical findings in canine parvirus disease.
Histologically marked depletion of lymph nodes and spleen as well as panmyelophthisis of the bone marrow are seen.
Typical findings in the gut are atrophy of the villi, dilated krypts with intraluminal desquamated epithelia and regenerative hyperplasia in other krypts.
Immunohistochemically parvovirus antigen is identified within the affected epithelia in dogs and cats.
Toxoplasmosis is a zoonotic parasitic disease which may affect various species. In immunodeficient individuals a systemic infection of brain, lungs, liver and spleen may occur. In clinically suspected cases serological diagnosis is possible.
Immunohistochemically the cysts and trophozoites of toxoplasma can be identified within the tissue.
Immunochistochemistry is a very specific method to detect infectious agents within the formalin fixed tissue. Histological investigation has to be performed previously in any case.