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ISSN: 0975-8585
September - October 2015 RJPBCS 6(5) Page No. 1001
Research Journal of Pharmaceutical, Biological and Chemical
Sciences
Proposed Therapy For Disease That May Cross Species Barrier Leading To
Infection In Human.
Kirtypal Singh, Ravi Kant Pathak, and Nishtha Pandey*.
School of Biotechnology and Biosciences, Lovely Professional University, Phagwara, Punjab, India.
ABSTRACT
Infection is a term used to describe the invasion of a host organism by some disease causing pathogen
viz., virus, bacteria etc. Pathogens evolve to expand their habitat by targeting orthologs of closely related
species. Many of the infectious diseases that are prevailing in Homo sapiens are consequence of transmission
across species. This work focused on identification of such infectious disease that may cross the species barrier
in future to infect the human population. In this study various non-human mammalian diseases were studied;
detailed genomic and proteomic analysis of African swine fever viral strains was carried out. It was observed
that the African swine fever virus attachment protein p12 possess characteristics similar to epitopic region of
Plasmodium falciparum antigen. This study predicts an approach to evade African swine fever infection in
Homo sapiens.
Keywords: african swine fever, infection, species barrier, zoonosis.
*Corresponding author
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INTRODUCTION
African Swine fever (ASF), also known as, haemorrhagic fever is highly infectious disease of Sus scrofa,
caused by African Swine Fever Virus (ASFV). The ASFV is a large, double stranded DNA virus that is only
member of family Asfarviridae which infects pigs, warthogs [1]. The initial clinical symptoms manifested are
high fever for few days followed by other symptoms such as loss of appetite. During infection white colour of
Sus scrofa turns blueish-purple due to frequent haemorrhages on the ears and abdomen. Other, accompanied
acute symptoms are shivering, coughing and breathing abnormality with 100% morality rate of the infected
animal [2]. ASF infection is diagnosed in infected animals by molecular characterization of ASFV specific genes
[3]. Probe based characterization or sequencing can also be done for the confirmatory test of infection in an
animal. There are no published reports of ASFV infection in Homo sapiens but, in one study novel sequences of
DNA similar to ASFV genome has been detected in sewage found near human population and serum of human
patients suffering from acute febrile illness (AFI) [4]. Immune system of Sus scrofa is similar to Homo sapiens.
Major organs of Sus scrofa are harvested for their xenotransplantation in Homo sapiens due to high similarity
between the organ system and immune system [5]. Therefore the pathogens are likely to be quite similar for
Homo sapiens and Sus scrofa. The findings raise the alarming concern of chances of zoonosis of ASF as a new
emerging disease in human population.
This work focused on functional analysis of ASFV proteins [Tab.1] and comparison of ASFV protein
with human and other pathogens for target identification. Effective vaccine can be developed against such
pathogen which has not yet evolved to virulence state. ASFV adapts receptor mediated endocytosis to enter
into the host cells [6]. African swine fever virus causes cytoplasm membrane perturbation, blabbing and ruffles
to enter into host cell. p12, the envelope protein of ASFV, helps in initial binding of ASFV particle to the host
cell surface receptor [7].
MATERIALS AND METHODS
Different strains of ASFV that infect either domestic or wild Sus scrofa were searched and compared
to find out the degree of conservation. Genomic sequences of ASFV strains were searched from GenBank [8]
database. Protein product of the coding regions present in the genomic sequence of African swine fever virus
(ASFV) were searched in UniProtKB [9]; functional analysis of 61 proteins was carried out and compared across
8 strains of ASFV. Protein products were searched for each strain of AFSV. Out of the 61 proteins, p12
envelope protein of ASFV was selected for the study because; it is the one of the structural protein of virus
that helps in initial binding of the virus particle to the host cell surface receptor [10]. Binding of virus particle to
host cell surface receptor initiates further infection mechanism. To understand the degree of conservation
across ASFV strains, multiple sequence alignment of p12 sequences was performed for reported strains of
ASFV. Multiple sequence alignment was performed with default parameters of EMBL-EBI ClustalW2 [11]. The
envelope protein p12 of ASFV was compared with the other species to find similarity. Both nucleotide and
protein BLAST [12] were carried out for sequence based database similarity search. While performing
comparison ASFV was excluded as organism to find match in other species. Protein p12 was also compared
with its functional equivalent hemagglutinin of H1N1. Hemagglutinin of H1N1 binds to sialic acid-containing
ISSN: 0975-8585
September - October 2015 RJPBCS 6(5) Page No. 1003
receptors on the host cell surface, bringing about the attachment of the virus particle to the cell. The p12
sequence was scanned against Pfam [13] for family and domains characterization. Based on these
characteristics some targets were identified for therapeutic purpose.
RESULTS AND DISCUSSION
Genome sequence data of 8 strains with accession number and size has been represented in table 2.
Out of the 61 proteins searched for different ASFV strains, p12 was considered as an important protein for
study because of its high degree of conservation across strains and role as the initiator of infection process.
Fig.1. shows the multiple sequence alignment of p12 from 8 strains; length of protein varies from 61 to 62.
95%(59 out of 62) identity is shared among all the sequences, the substitutions observed are also conservative
or semi conservative in nature. Interestingly, the protein sequences are observed to be rich in two
consecutively same residues (e.g., SS, GG, VV, II etc.). High degree of conservation also supports the
indispensable function of p12 in infection and disease manifestation. Comparison of p12 (P32510) with other
proteins of pathogenic source did not show any significant match; the best match had score 37.4 and E value
0.66. Out of the 13 protein matched in database similarity search 11 were hypothetical or predicted proteins
[Fig. 2]. While simple protein BLAST did not give significant match with any sequence, putative conserved
domain was detected in the protein. The domain matched with Pfam record (pfam02009) of Rifin_STEVOR
family. The family is several multicopy gene family for Plasmodium falciparum. The STEVOR and rif proteins are
the members of large superfamily that encodes for various surface antigens. This family is a member of
multigene family known as var which are expressed on the surface of infected red blood cells [14]. Table 3
summarizes list of sequences that are coded on the surface of infected erythrocytes during infection of
Plasmodium falciparum. Epitopic regions of the proteins for both MHC I and MHC II were predicted using the
software Propred [15]. The epitopic region predicted showed high similarity with p12 conserved domain region
of rifin stevor [Fig. 3].
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CONCLUSIONS
ASFV causes infection in Sus scrofa. Though infection is not reported in human, novel DNA sequences
similar to ASFV genome have been detected from human sources. Such findings raise the doubt of infection in
human in future. ASFV attachment protein has not shown any significant match with human pathogens but,
the protein has properties similar to known antigenic sequences. Hence, it can be concluded that segments of
p12 including position 18-25 can be used to design peptide based vaccines against ASFV infection in human.
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