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Monday, July 08, 2013

Russia Bans Hogs and Pork From Belarus on African Swine Fever

African Swine Fever Virus as a Human Pathogen

Background on African Swine Fever Virus as a human pathogen:

"African Swine fever is an endemic disease in sub-Saharan Africa and many other parts of the developing world. It is caused by the African Swine virus that primarily replicates in macrophages and monocytes leading to the impairment of the structure and function of the immune system of the infected organisms. Until now the African Swine epidemic continues to spread despite all efforts to contain it. Thus, there is an objective need for effective, safe and affordable preventive and therapeutic approaches, in particular for effective vaccines, to control and eventually eradicate this disease. Since the characteristic feature of the African Swine virus is to impair the immune system and to cause immune deficiencies in its hosts the development of vaccines and other therapeutic approaches against the African Swine virus has implications for other immune deficiencies or diseases. Several other viruses are also known to cause immunodeficiency-like syndromes in humans, including cytomegalovirus, Epstein Barr Virus and others. Moreover, a series of cases of so-called "idiopathic" immunodeficiencies have been documented that display CD4+T-lymphocytopenia with opportunistic infections, but show no evidence of HIV infection. Since antibodies for the African Swine virus have been detected in humans, the possibility of human infection with the African Swine virus exists and may thus far have escaped any systematic screening. Thus, any preventive and therapeutic approach to African Swine fever can have far-reaching implications to control immune deficiency conditions in humans."

Detection of Novel Sequences Related to African Swine Fever Virus in Human Serum and Sewage.

Loh J, Zhao G, Presti RM, Holtz LR, Finkbeiner SR, Droit L, Villasana Z, Todd C, Pipas JM, Calgua B, Girones R, Wang D, Virgin HW.

Departments of Pathology & Immunology and Molecular Microbiology, Department of Medicine and Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri; Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania; Department of Microbiology, Faculty of Biology, University of Barcelona, Barcelona, Spain.

"The family Asfarviridae contains only a single virus species, African swine fever virus (ASFV). ASFV is a viral agent with significant economic impact due to its devastating effects on populations of domesticated pigs during outbreaks, but has not been reported to infect humans. We report here the discovery of novel viral sequences in human serum and sewage which are clearly related to the Asfarvirus family, but highly divergent from ASFV. Detection of these sequences suggests that greater genetic diversity may exist among Asfarviruses than previously thought, and raises the possibility that human infection by Asfarviruses may occur."

African Swine Fever Virus (Asfarviridae) sequences found in people with febrile illnesses

Virus Identification in Unknown Tropical Febrile Illness Cases Using Deep Sequencing
Dengue virus is an emerging infectious agent that infects an estimated 50–100 million people annually worldwide, yet current diagnostic practices cannot detect an etiologic pathogen in ∼40% of dengue-like illnesses. Metagenomic approaches to pathogen detection, such as viral microarrays and deep sequencing, are promising tools to address emerging and non-diagnosable disease challenges. In this study, we used the Virochip microarray and deep sequencing to characterize the spectrum of viruses present in human sera from 123 Nicaraguan patients presenting with dengue-like symptoms but testing negative for dengue virus. We utilized a barcoding strategy to simultaneously deep sequence multiple serum specimens, generating on average over 1 million reads per sample. We then implemented a stepwise bioinformatic filtering pipeline to remove the majority of human and low-quality sequences to improve the speed and accuracy of subsequent unbiased database searches. By deep sequencing, we were able to detect virus sequence in 37% (45/123) of previously negative cases. These included 13 cases with Human Herpesvirus 6 sequences. Other samples contained sequences with similarity to sequences from viruses in the Herpesviridae, Flaviviridae, Circoviridae, Anelloviridae, Asfarviridae, and Parvoviridae families. In some cases, the putative viral sequences were virtually identical to known viruses, and in others they diverged, suggesting that they may derive from novel viruses. These results demonstrate the utility of unbiased metagenomic approaches in the detection of known and divergent viruses in the study of tropical febrile illness.

Detection of African swine fever virus-like sequences in ponds in the Mississippi Delta through metagenomic sequencing

" . .. further study is needed to characterize their potential risks to both public health and agricultural development."

ASF virus, adapted to grow in VERO cells, produces a strong cytopathic effect in human macrophages leading to cell destruction.

Could this happen to macrophages in humans infected with African Swine Fever Virus?

Cytokines produced by cells of the immune system, including macrophages, can influence inflammatory responses to viral infection. This has been exploited by viruses, which have developed strategies to direct the immune response towards ineffective responses. African swine fever virus (ASFV) is a double-stranded DNA virus that infects macrophages of domestic swine. In this study, primary cells of monocyte macrophage lineage were obtained from the lungs, peritoneum or blood of domestic swine and, after infection with ASFV, supernatants were tested for cytokines using biological assays. The cytokine transforming growth factor-beta (TGF-beta) was detected after infection of macrophage preparations, but tumour necrosis factor (TNF) and interleukin-1 (IL-1) were not detected. ASFV-infected and uninfected macrophage populations were also tested to assess their ability to respond to cytokines by enhancing production of superoxide in the respiratory burst mechanism. Responses to interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS) were suppressed in macrophage populations infected with virus, even at low multiplicities of infection. Addition of TGF-beta to uninfected macrophages resulted in a similar suppression of response, but antibody to TGF-beta did not prevent suppression induced by virus. These results are discussed in relation to the pathology of African swine fever.


Will African Swine Fever affect the natural killer cells in humans infected with it?

"The natural killing of the human myeloid leukaemia cell line by pig mononuclear cells was investigated in an 18 hr assay; the most active natural-killer (NK) effectors were those cells not adhering to nylon-wool columns or rosetting with sheep red blood cells. Mononuclear cells cultured in the presence of African swine-fever virus maintained NK activity. Pigs infected with African swine-fever virus exhibited a suppressed NK activity, possibly due to the sensitivity of NK cells to increased temperatures. The possible role of NK cells in recovery from African swine fever is discussed."


How to Test for African Swine Fever Virus

Laboratory Diagnosis

Because ASF can easily be confused with other important diseases of swine, obtaining samples for laboratory diagnosis is an important step in confirming the illness.
Samples of the following should be sent to the laboratory (they should be kept as cold as possible, without freezing, during transport):
  • Blood in anticoagulant (heparin or ethylenediaminetetraacetic acid [EDTA])
  • Spleen
  • Tonsil
  • Kidney
  • Lymph nodes
The following tests are available to identify the ASF virus:
  • Hemadsorption (HAD) test
  • Polymerase chain reaction (PCR)
  • Pig inoculation (no longer recommended)
The following tests can be used to test for antibodies in recovering pigs about 8 to 21 days after infection:
  • Enzyme-linked immunosorbent assay (ELISA) (preferred test for international trade)
  • Indirect fluorescent antibody test (FAT)
  • Immunoblotting test
  • Counter-immunoelectrophoresis (immunoelectroosmophoresis)
For more information on any of these tests, see References: OIE: Manual of standards for diagnostic tests and vaccines.

John Beldekas's research on African Swine Fever Virus as a human infection
Spin Magazine on John Beldekas

Florida Pig Farm Poses Riddle

"AIDS victims and pigs stricken with chronic African swine fever have common characteristics, Beldekas said, including fever, abnormally large lymph nodes, skin lesions, immune-related pneumonia, and a reduction of white blood cells. Both diseases can be spread through exposure to infected blood, blood products and semen, Beldekas said, but the animal virus can also be transmitted by infected ticks. Accordingly, they say, the animal virus may somehow be a factor in the transmission of AIDS, which could have spread from infected pigs to humans through tick bites, and then from human to human through sexual contact or direct infection of blood."

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